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Basic Understanding Of OSI Layers

The OSI Network Model Standard

The International Standards Organization (ISO) has defined a standard called the

Open Systems Interconnection (OSI) reference model. This is a seven layer

architecture listed below. Each layer is considered to be responsible for a different

part of the communications. This concept was developed to accommodate changes

in technology. The layers are arranged here from the lower levels starting with the

physical (hardware) to the higher levels.

1. Physical Layer - The actual hardware.

2. Data Link Layer - Data transfer method (802x ethernet). Puts data in framesand ensures error free transmission. Also controls the timing of the network

transmission. Adds frame type, address, and error control information. IEEE

divided this layer into the two following sublayers.

1. Logical Link control (LLC) - Maintains the Link between two

computers by establishing Service Access Points (SAPs) which are a

series of interface points. IEEE 802.2.

2. Media Access Control (MAC) - Used to coordinate the sending of data

between computers. The 802.3, 4, 5, and 12 standards apply to this

layer. If you hear someone talking about the MAC address of a networkcard, they are referring to the hardware address of the card.

3. Network Layer - IP network protocol. Routes messages using the best path

available.

4. Transport Layer - TCP, UDP. Ensures properly sequenced and error free

transmission.

5. Session Layer - The user's interface to the network. Determines when the

session is begun or opened, how long it is used, and when it is closed.

Controls the transmission of data during the session. Supports security and

name lookup enabling computers to locate each other.

6. Presentation Layer - ASCII or EBCDEC data syntax. Makes the type of datatransparent to the layers around it. Used to translate date to computer specific

format such as byte ordering. It may include compression. It prepares the data,

either for the network or the application depending on the direction it is going.

7. Application Layer - Provides services software applications need. Provides the

ability for user applications to interact with the network.

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Many protocol stacks overlap the borders of the seven layer model by operating at

multiple layers of the model. File Transport Protocol (FTP) and telnet both work at

the application, presentation, and the session layers.

The Internet, TCP/IP, DOD Model

This model is sometimes called the DOD model since it was designed for the

department of defense It is also called the TCP/IP four layer protocol, or the internet

protocol. It has the following layers:

1. Link - Device driver and interface card which maps to the data link and

physical layer of the OSI model.

2. Network - Corresponds to the network layer of the OSI model and includes

the IP, ICMP, and IGMP protocols.

3. Transport - Corresponds to the transport layer and includes the TCP and UDPprotocols.

4. Application - Corresponds to the OSI Session, Presentation and Application

layers and includes FTP, Telnet, ping, Rlogin, rsh, TFTP, SMTP, SNMP, DNS,

your program, etc.

Please note the four layer TCP/IP protocol. Each layer has a set of data that it

generates.

1. The Link layer corresponds to the hardware, including the device driver and

interface card. The link layer has data packets associated with it depending onthe type of network being used such as ARCnet, Token ring or ethernet. In our

case, we will be talking about ethernet.

2. The network layer manages the movement of packets around the network and

includes IP, ICMP, and IGMP. It is responsible for making sure that packages

reach their destinations, and if they don't, reporting errors.

3. The transport layer is the mechanism used for two computers to exchange data

with regards to software. The two types of protocols that are the transport

mechanisms are TCP and UDP. There are also other types of protocols for

systems other than TCP/IP but we will talk about TCP and UDP in this

document.

4. The application layer refers to networking protocols that are used to support

various services such as FTP, Telnet, BOOTP, etc. Note here to avoid

confusion, that the application layer is generally referring to protocols such as

FTP, telnet, ping, and other programs designed for specific purposes which are

governed by a specific set of protocols defined with RFC's (request for

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comments). However a program that you may write can define its own data

structure to send between your client and server program so long as the

program you run on both the client and server machine understand your

protocol. For example when your program opens a socket to another machine,

it is using TCP protocol, but the data you send depends on how you structure

it.

Data Encapsulation, a Critical concept to be understood

When starting with protocols that work at the upper layers of the network models,

each set of data is wrapped inside the next lower layer protocol, similar to wrapping

letters inside an envelope. The application creates the data, then the transport layer

wraps that data inside its format, then the networklayer wraps the data, and finally

the link(ethernet) layer encapsulates the data and transmits it.

To continue, you should understand the definition of a client and server with regards

to networking. If you are a server, you will provide services to a client, in much the

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same way as a private investigator would provide services to their clients. A client

will contact the server, and ask for service, which the server will then provide. The

service may be as simple as sending a single block of data back to the client. Since

there are many clients, a server must be constantly ready to receive client requests,

even though it may already be working with other clients. Usually the client program

will operate on one computer, while the server program will operate on another

computer, although programs can be written to be both a client and a server.

Lets say you write a client chat program and a server chat program to be used by two

people to send messages between their machines. You run the server program on

machine B, and the client program on machine A. Tom is on machine A and George

is on machine B. George's machine is always ready to be contacted, but cannot

initiate a contact. Therefore if George wants to talk to Tom, he cannot, until Tom

contacts him. Tom, of course can initiate contact at any time. Now you decide to

solve the problem and merge the functionality of the two programs into one, so bothparties may contact the other. This program is now a client/server program which

operates both as a client and a server. You write your code so when one side initiates

contact, he will get a dialog box, and a dialog box will pop up on the other side. At

the time contact is initiated, a socket is opened between the two machines and a

virtual connection is established. The program will let the user (Tom) type text into

the dialog window, and hit send. When the user hits send, roughly the following will

happen.

1. Your program will pass Tom's typed text in a buffer, to the socket. This

happens on machine A.2. The underlying software (Code in a library called by a function your program

used to send the data) supporting the socket puts the data inside a TCP data

packet. This means that a TCP header will be added to the data. This header

contains a source and destination port number along with some other

information and a checksum. Deamon programs (Daemon definition at the

bottom of this page) may also work at this level to sort packages based on port

number (hence the TCP wrapper program in UNIX and Linux).

3. The TCP packet will be placed inside an IP data packet with a source and

destination IP address along with some other data for network management.This may be done by a combination of your library function, the operating

system and supporting programs.

4. The IP data packet is placed inside an ethernet data packet. This data packet

includes the destination and source address of the network interface cards

(NIC) on the two computers. The address here is the hardware address of the

respective cards and is called the MAC address.

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5. The ethernet packet is transmitted over the network line.

6. Assuming there is a direct connection between the two computers, the

network interface card on machine B, will recognize its MAC address and

grab the data.

7. The IP data packet will be extracted from the ethernet data packet. A

combination of deamons and the operating system will perform this operation.

8. The TCP data packet will be extracted from the IP data packet. A combination

of deamons, the operating system, and libraries called by your program will

perform this function.

9. The data will be extracted from the TCP packet. Your program will then

display the retrieved data (text) in the text display window for George to read.

Be aware that for the sake of simplicity, we are excluding details such as error

management, routing, and identifying the hardware address of the NIC on the

computer intended to receive the data. Also we are not mentioning the possiblerejection of service based on a packet's port number or sender's IP address.

A deamon program is a program that runs in the background on a computer

operating system. It is used to perform various tasks including server functions. It is

usually started when the operating system is booted, but a user or administrator may

be able to start or stop a daemon at any time.

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Network Devices

Repeaters, Bridges, Routers, and Gateways

Network Repeater

A repeater connects two segments of your network cable. It retimes and regenerates

the signals to proper amplitudes and sends them to the other segments. When talking

about, ethernet topology, you are probably talking about using a hub as a repeater.

Repeaters require a small amount of time to regenerate the signal. This can cause a

propagation delay which can affect network communication when there are several

repeaters in a row. Many network architectures limit the number of repeaters that can

be used in a row. Repeaters work only at the physical layer of the OSI network

model.

Bridge

A bridge reads the outermost section of data on the data packet, to tell where the

message is going. It reduces the traffic on other network segments, since it does not

send all packets. Bridges can be programmed to reject packets from particular

networks. Bridging occurs at the data link layer of the OSI model, which means the

bridge cannot read IP addresses, but only the outermost hardware address of the

packet. In our case the bridge can read the ethernet data which gives the hardware

address of the destination address, not the IP address. Bridges forward all broadcastmessages. Only a special bridge called a translation bridge will allow two networks

of different architectures to be connected. Bridges do not normally allow connection

of networks with different architectures. The hardware address is also called the

MAC (media access control) address. To determine the network segment a MAC

address belongs to, bridges use one of:

Transparent Bridging - They build a table of addresses (bridging table) as they

receive packets. If the address is not in the bridging table, the packet is

forwarded to all segments other than the one it came from. This type of bridge

is used on ethernet networks. Source route bridging - The source computer provides path information inside

the packet. This is used on Token Ring networks.

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Network Router

A router is used to route data packets between two networks. It reads the information

in each packet to tell where it is going. If it is destined for an immediate network it

has access to, it will strip the outer packet, readdress the packet to the proper

ethernet address, and transmit it on that network. If it is destined for another network

and must be sent to another router, it will re-package the outer packet to be received

by the next router and send it to the next router. The section on routing explains the

theory behind this and how routing tables are used to help determine packet

destinations. Routing occurs at the network layer of the OSI model. They can

connect networks with different architectures such as Token Ring and Ethernet.

Although they can transform information at the data link level, routers cannot

transform information from one data format such as TCP/IP to another such as

IPX/SPX. Routers do not send broadcast packets or corrupted packets. If the routing

table does not indicate the proper address of a packet, the packet is discarded.

Brouter

There is a device called a brouter which will function similar to a bridge for network

transport protocols that are not routable, and will function as a router for routable

protocols. It functions at the network and data link layers of the OSI network model.

Gateway

A gateway can translate information between different network data formats ornetwork architectures. It can translate TCP/IP to AppleTalk so computers supporting

TCP/IP can communicate with Apple brand computers. Most gateways operate at the

application layer, but can operate at the network or session layer of the OSI model.

Gateways will start at the lower level and strip information until it gets to the

required level and repackage the information and work its way back toward the

hardware layer of the OSI model. To confuse issues, when talking about a router that

is used to interface to another network, the word gateway is often used. This does

not mean the routing machine is a gateway as defined here, although it could be.

Network bridge

A network bridge connects multiple network segments at the data link layer(layer 2)

of the OSI model. Bridges are similar to repeaters ornetwork hubs, devices that

connect network segments at thephysical layer, however a bridge works by using

bridging where traffic from one network is managed rather than simply rebroadcast

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to adjacent network segments. In Ethernet networks, the term "bridge" formally

means a device that behaves according to the IEEE 802.1D standard - this is most

often referred to as a network switch in marketing literature.

Since bridging takes place at the data link layer of the OSI model, a bridge processes

the information from each frame of data it receives. In an Ethernet frame, thisprovides the MAC address of the frame's source and destination. Bridges use two

methods to resolve the network segment that a MAC address belongs to.

Transparent bridging This method uses a forwarding database to send frames

across network segments. The forwarding database is initially empty and entries

in the database are built as the bridge receives frames. If an address entry is not

found in the forwarding database, the frame is rebroadcast to all ports of the

bridge, forwarding the frame to all segments except the source address. By means

of these broadcast frames, the destination network will respond and a route will

be created. Along with recording the network segment to which a particularframe is to be sent, bridges may also record a bandwidth metric to avoid looping

when multiple paths are available. Devices that have this transparent bridging

functionality are also known as adaptive bridges.

Source route bridging With source route bridging two frame types are used in

order to find the route to the destination network segment. Single-Route (SR)

frames comprise most of the network traffic and have set destinations, while All-

Route(AR) frames are used to find routes. Bridges send AR frames by

broadcasting on all network branches; each step of the followed route is

registered by the bridge performing it. Each frame has a maximum hop count,

which is determined to be greater than the diameterof the network graph, and is

decremented by each bridge. Frames are dropped when this hop count reaches

zero, to avoid indefinite looping of AR frames. The first AR frame which reaches

its destination is considered to have followed the best route, and the route can be

used for subsequent SR frames;the other AR frames are discarded. This method

of locating a destination network can allow for indirect load balancing among

multiple bridges connecting two networks. The more a bridge is loaded, the less

likely it is to take part in the route finding process for a new destination as it will

be slow to forward packets. A new AR packet will find a different route over a

less busy path if one exists. This method is very different from transparent bridgeusage, where redundant bridges will be inactivated; however, more overhead is

introduced to find routes, and space is wasted to store them in frames. A switch

with a faster backplane can be just as good for performance, if not for fault

tolerance

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Advantages of network bridges

Self configuring

Primitive bridges are often inexpensive

Reduce size of collision domain

Transparent to protocols above the MAC layer

Allows the introduction of management - performance information and access

control

LANs interconnected are separate and physical constraints such as number of

stations, repeaters and segment length don't apply

Disadvantages of network bridges

Does not limit the scope of broadcasts

Does not scale to extremely large networks

Buffering introduces store and forward delays - on average traffic destined for

bridge will be related to the number of stations on the rest of the LAN

Bridging of different MAC protocols introduces errors

Because bridges do more than repeaters by viewing MAC addresses, the extra

processing makes them slower than repeaters

Bridges are more expensive than repeaters

Layer 1 Hubs versus Higher Layer Switches

An Ethernet hub, or repeater, is a fairly unsophisticated broadcast device, and

rapidly becoming obsolete. Hubs do not manage any of the traffic that comes

through them. Any packet entering a port is broadcast out or "repeated" on every

other port, save the port of entry. Since every packet is repeated on every other port,packet collisions result--which slows down the network.

Hubs have actually become hard to find, due to the widespread use of switches.

There are specialized applications where a hub can be useful, such as copying traffic

to multiple network sensors. There is no longer any significant price difference

between a hub and a low-end switch.

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Layer 2A single LAN switch, operating at the MAC sublayer of the data link layer, may

interconnect a small number of devices in a home or office. This is a trivial case ofbridging, in which the switch learns the MAC address of each connected device.

Compared to shared-medium LANs, a switch using microsegmentation prevents

collisions on an Ethernet, and can provide effectively simultaneous paths among

multiple devices. Single switches also can provide extremely high performance in

specialized applications such as storage area networks

Switches may also interconnect using a spanning-tree protocol that allows the best

path to be found within the constraint that it is a tree. In contrast to routers, bridges

only can have topologies with one active path between two points. The older IEEE

802.1d spanning tree protocol could be quite slow, with forwarding stopping for 30-

90 seconds while the spanning tree reconverged. A Rapid Spanning Tree Protocolwas introduced as IEEE 802.1w, but the newest edition of IEEE 802.1d-2004, adopts

the 802.1w extensions as the base standard.

Once a layer 2 switch learns the topology through a spanning tree protocol, it

forwards data link layer frames using some variant of bridging. There are four

forwarding methods a Layer 2 switch can use:

Store and forward - The switch buffers and, typically, performs a checksum on each

frame before forwarding it on.

Cut through - The switch only reads up to the frame's hardware address before

starting to forward it. There is no error checking with this method.Fragment free - A method which attempts to retain the benefits of both "Store and

Forward" and "Cut-through". Fragment Free checks the first 64 bytes of the frame,

where addressing information is stored. This way the frame will always reach its

intended destination. Error checking of the actual data in the packet is left for the

end device in Layer 3 or Layer 4 (OSI), typically a router.

Adaptive switching - A method of automatically switching between the other three

modes.

Note that "cut through" switches have to fall back to "store and forward" if the

outgoing port is busy at the time the packet arrives.

Note that these forwarding methods are not controlled by the user and are configuredonly by the switch itself.

Layer 3Layer 3 switch is a marketing term for a router, typically a router optimized for

Ethernet interfaces. Like other switches, it connects devices to single ports for

microsegmentation. The ports normally operate in full duplex.

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Switches, even primarily layer 2 switches, can be aware of layer 3 multicast and

increase efficiency by delivering the traffic of a multicast group only to ports where

the attached device has signaled that it wants to listen to that group. In a switch not

aware of multicasting and broadcasting, frames are also forwarded on all ports of

each broadcast domain, but in the case of IP multicast this causes inefficient use of

bandwidth. To work around this problem some switches implement IGMP snooping.

Network Layer (Layer 3)

The third-lowest layer of the OSI Reference Model is the networklayer. If the datalink layer is the one that basically defines the boundaries of what is considered a

network, the network layer is the one that defines how internetworks (interconnected

networks) function. The network layer is the lowest one in the OSI model that isconcerned with actually getting data from one computer to another even if it is on a

remote network; in contrast, the data link layer only deals with devices that are local

to each other.

While all of layers 2 through 6 in the OSI Reference Model serve to act as fences

between the layers below them and the layers above them, the network layer is

particularly important in this regard. It is at this layer that the transition really begins

from the more abstract functions of the higher layerswhich don't concern

themselves as much with data deliveryinto the specific tasks required to get data

to its destination. The transport layer, which is related to the network layer in anumber of ways, continues this abstraction transition as you go up the OSI

protocol stack.

Network Layer Functions :Some of the specific jobs normally performed by the network layer include:

Logical Addressing: Every device that communicates over a network has associated

with it a logical address, sometimes called a layer three address. For example, on the

Internet, the Internet Protocol (IP) is the network layer protocol and every machine

has an IP address. Note that addressing is done at the data link layer as well, but

those addresses refer to local physical devices. In contrast, logical addresses are

independent of particular hardware and must be unique across an entire internet

work.

Routing: Moving data across a series of interconnected networks is probably the

defining function of the network layer. It is the job of the devices and software

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routines that function at the network layer to handle incoming packets from various

sources, determine their final destination, and then figure out where they need to be

sent to get them where they are supposed to go. I discuss routing in the OSI model

more completely in this topic on the topic on indirect device connection, and show

how it works by way of an OSI model analogy.

Datagram Encapsulation: The network layer normally encapsulates messages

received from higher layers by placing them into datagrams (also called packets)

with a network layer header.

Fragmentation and Reassembly: The network layer must send messages down to

the data link layer for transmission. Some data link layer technologies have limits on

the length of any message that can be sent. If the packet that the network layer wants

to send is too large, the network layer must split the packet up, send each piece to the

data link layer, and then have pieces reassembled once they arrive at the network

layer on the destination machine. A good example is how this is done by the Internet

Protocol.Error Handling and Diagnostics: Special protocols are used at the network layer to

allow devices that are logically connected, or that are trying to route traffic, to

exchange information about the status of hosts on the network or the devices

themselves.

Layer-specific functionality

A modular network switch with 3 network modules (a total of 24 Ethernet and 14

Fast Ethernet ports) and one power supply.

While switches may learn about topologies at many layers, and forward at one or

more layers, they do tend to have common features. Other than for computer-room

very high performance applications, modern commercial switches use primarily

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Ethernet interfaces, which can have different input and output speeds of 10, 100,

1000 or 10000 megabits per second. Switch ports almost always default to full-

duplex operation, unless there is a requirement for interoperability with devices that

are strictly half duplex. Half-duplex means that the device can only send or receive

at any given time, whereas full-duplex can send and receive at the same time.

At any layer, a modern switch may implement Power over Ethernet (POE), which

avoids the need for attached devices, such as an IP telephone or Wireless Access

Point, to need a separate power supply. Since switches can have redundant power

circuits connected to uninterruptible power supplies, the connected device can

continue operating even when regular office power fails.

Network Routing

Simple Networking Routing and Routers

This section will explain routing in simple terms with some simple standard rules.

There may be exceptions to these rules, but for introductory purposes we will keep

the first example simple. Please be aware, that the examples in this section are

working examples, but more complexity may be added when a larger network is

considered, and multiple data routes become available.

Each network interface card (NIC) has a specific address which is an IP address or

number. When data is sent between two computers, the data must be sent in a

package that has the address of the intended receiver (IP) on it. It is like an envelope

(ethernet) with the sender's and recipient's address on it. There is somewhat of a

difference, however. When the computer intends to send a packet, it first checks its

routing table to see if the intended data must be sent through a gateway. Many

computers only have a simple routing table, which is built from the network mask

and the gateway information entered, when you set your computer up to do

networking. The computer, when set up for networking, must be assigned an IP

address, netmask, and default gateway. This may be done manually or done

automatically using Dynamic Host Configuration Protocol (DHCP) to assign thisinformation to the computer when it boots. DCHP is described in another section. If

the computer determines that the packet must be sent to a gateway, it puts it in a

special packet (ethernet) for that gateway, with the actual recipient's address

wrapped inside.

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In the above paragraph, data packets are equated to a letter with an envelope. For

this type of thinking, the envelope would be similar to the ethernet, SLIP, or PPP

packet which encapsulates the IP packet. The IP packet and its encapsulated data

would similar to a letter. Here's generally what happens when a package is sent:

The sending computer checks the IP part of the package to see the

sender's IP address, and based on the address and instructions in its

routing table will do one of the following:

1. Send the packet to the ethernet address of the intended recipient. The

following will happen:

1. The ethernet card on the receiving computer will accept the packet.

2. The other network levels (IP, TCP) will open the packet and use it

according to filtering and other programming instructions.

2. Send the packet to the ethernet address of a router, depending on theinstructions in the routing table.

1. The ethernet card on the router will accept the packet.

2. The IP level of the router will look at the packet's IP address and

determine according to its routing table where to send the packet next.

It should send it to another router or to the actual recipient.

3. The router will encapsulate the IP packet in another ethernet packet

with the ethernet address of the next router or the intended recipient.

4. Router hops will continue until the packet is sent on a network where

the intended recipient is physically located unless the packet expires.

5. The ethernet card on the receiving computer will accept the packet.

The other network levels (IP, TCP) will open the packet and use it according to

filtering and other programming instructions.

Lets say you enter an IP address of 10.1.20.45 and a netmask of 255.255.0.0. This

means you are on the network 10.1.0.0 (I show it as 10.1.x.x, the X's mean don't care

conditions). The machine's IP address and netmask, together define the network, that

it's NIC is on. Therefore any machine that fits in the address range provided under

10.1.x.x can be accessed directly from your NIC, and any that are not in this number

range, such as 10.3.34.67 cannot be accessed directly and must be sent to a gateway

machine since it is on another network. Typically most machines will use their

netmask to make this determination which means if the address does not match their

known network, the package will be sent to that machine's default gateway in a

special package meant for a router. It works similar to a post office. When you send

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a letter in your town, you put it in the local slot. It can be delivered to someone else

in your town (network), but if you are sending to another town (network), you put

the letter in the out of town slot (default gateway), then the mail personnel put it in a

special container or box and send it to a main town (gateway), which then decides

where to send it based on its address. Although this simple network and default

gateway may be common, specific computers or gateways can have much more

complex rules for routing that allow exceptions to this example.

Please be aware that in order to be forwarded, data packets must be addressed to a

router. They cannot just be sent to the recipient's address out to a network. The router

does not pick packets off the network and forward them. If a packet is sent on a

network and a valid recipient is not on that network, there will be no response. This

will be demonstrated in the next section where a subnetwork will be described.

To keep routing simple, most networks are structured as shown below. Generally, thehigher networks are 10.x.x.x, then the next are 10.0-254.x.x, then 10.0-254.0-254.x.

The number 10 is used as an example Class A network. This numbering scheme

keeps routing simple and is the least confusing but networks can be set up in other

ways. In the diagram below, only gateways and their networks are shown.

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In my simple network example below I vary from convention and make network

192.168.2.x be below network 192.168.1.x. causing traffic between the internet and

192.168.2.x to go through the network 192.168.1.x. Normally the network

192.168.1.x would be 192.168.x.x, but this will show you that there can be many

variants that will work as long as you have thought your layout through well, and set

your routing tables up in your gateways correctly.

Display of some Commonly used Routers

Routers for Service Small, Midsized and Large Businesses

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Routers for Service Providers

TYPES OF DEVICES:

ROUTER:

History

The very first device that acted as a router does today was called an IMP, whichstands for Interface Message Processor. The first functional IMP was placed at

UCLA on August 30, 1969 and was developed at BBN by the IMP team as part of

their contract to build out the original ARPANET. The IMP and the routers that

followed are what make the Internet possible.

The first multiprotocol router was created at Stanford University by a staff

researcher named William Yeager in January of 1980. As virtually all networking

now uses IP at the network layer, multiprotocol routers are largely obsolete. Routers

that handle both IPv4 and IPv6 arguably are multiprotocol, but in a far less variablesense than a router that processed AppleTalk, DECnet, IP, and Xerox protocols.

In the original era of routing (from the mid-1970s through the 1980s), general-

purpose mini-computers served as routers. Although general-purpose computers can

perform routing, modern high-speed routers are highly specialized computers,

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generally with extra hardware added to accelerate both common routing functions

such as packet forwarding and specialised functions such as IPsec encryption.

Still, there is substantial use of Linux and Unix machines, running open source

routing code, for routing research and selected other applications. While Cisco's

operating system was independently designed, other major router operating systems,

such as those from Juniper Networks and Extreme Networks, are extensively

modified but still have Unix ancestry.

Other changes also improve reliability, such as redundant control processors with

stateful failover, and using storage having no moving parts for program loading.

As much reliability comes from operational techniques for running critical

routers as it does to the router design itself. It is the best common practice, for

example, to use redundant uninterruptible power supplies for all critical network

elements, with generator backup for the batteries or flywheels of those powersupplies.

Contents

1) Function

2) Control Plane

2.1) Routing table

3) Application in network layer Routing

4)Types of routers

4.1 Routers for Internet connectivity and internal use

4.2 Small and Home Office (SOHO) connectivity

4.3 Enterprise Routers

4.3.1 Access

4.3.2 Distribution

4.3.3 Core

Function:

A more precise definition of a router is a computer networking device that

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interconnects separate logical subnets. Routers are now available in many types,

though all are fundamentally doing the same job. A router is a computer whose

software and hardware are usually tailored to the tasks of routing and forwarding,

generally containing a specialized operating system (e.g. Cisco's IOS or Juniper

Networks JunOS or Extreme Networks XOS), RAM, NVRAM, flash memory, and

one or more processors. High-end routers contain many processors and specialized

ASICs and do a great deal of parallel processing. However, with the proper software

(such as XORP or Quagga), even commodity PCs can act as routers.

Routers connect to two or more logical subnets, which do not necessarily map one-

to-one to the physical interfaces of the router

The term switch orlayer 3 switch or network switch often is used interchangeably

with router, but switch is really a marketing term without a rigorous technical

definition (though a switch is commonly understood as a network hub with switched

ports, which might or might not also perform additional routing functions).Routers operate in two different planes:

Control Plane, in which the router learns the outgoing interface that is most

appropriate for forwarding specific packets to specific destinations,

Forwarding Plane, which is responsible for the actual process of sending a

packet received on a logical interface to an outbound logical interface.

To understand the role of a router, understand that it does not, in a network of any

real complexity, take you directly to the destination. Instead, your information will

pass through a series of routers and intermediate subnets, each getting you one "hop"closer to the destination, until you reach the router that connects to the subnet that

contains your final destination.

As a simple analogy, assume that you want to travel from Washington DC to New

York City. Getting on a highway, you see an exit marked "US Capitol". That does

not get you closer to your destination, so you continue. Eventually, you see a sign

reading "Baltimore and New York". You take that exit, which leads you to another

freeway, where you pass a number of exits for destinations in suburban Maryland.

Eventually, you see an exit marked "Philadelphia and New York", and take that to

another highway. You repeat this process until you get into New York City, and thentake a local exit to your destination. In like manner, routers receive packets, look up

their destination addresses in routing tables that have entries that tell you the

interface that is one hop closer to the destination, and sends the packet out the

destination. This is characteristic of the Network Layer, which deals with hop-by-

hop communications as opposed to the end-to-end communications of the Transport

Layer.

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For the pure Internet Protocol (IP) forwarding function, router design tries to

minimize the state information kept on individual packets. Routers do maintain state

on routes, but not packets. Once a packet is forwarded, the router should retain no

more than statistical information about it. It is the sending and receiving endpoint

that keeps information on such things as errored or missing packets.

Forwarding decisions can involve decisions at layers other than the IP internetwork

layer or OSI layer 3. Again, the marketing term switch can be applied to devices that

have these capabilities. A function that forwards based on data link layer, or OSI

layer 2, information, is properly called a bridge, or layer 2 switch. A physical device

called a router may also have the capability to forward based on information at other

layers.

Control Plane

Control Plane processing leads to the construction of what is variously called a

routing table or routing information base (RIB). The RIB may be used by the

Forwarding Plane to look up the outbound interface for a given packet, or,

depending on the router implementation, the Control Plane may populate a separate

Forwarding Information Base (FIB) with destination information. RIBs are

optimized for efficient updating with control mechanisms such as routing protocols,

while FIBs are optimized for the fastest possible lookup of the information needed to

select the outbound interface.

The Control Plane constructs the routing table from knowledge of the up/down

status of its local interfaces, from hard-coded static routes, and from exchanging

routing protocol information with other routers. It is not compulsory for a router to

use routing protocols to function, if for example it was configured solely with static

routes. The routing table stores the best routes to certain network destinations, the

"routing metrics" associated with those routes, and the path to the next hop router.

Routers do maintain state on the routes in the RIB/routing table, but this is quite

distinct from not maintaining state on individual packets that have been forwarded.

Applications in Network Layer Routing

Forwarding Information Base:

A Forwarding Information Base (FIB), also known as a forwarding table, is most

commonly used in networkbridging, routing, and similar functions to find the

proper interface to which the input interface should send a packet to be transmitted

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by the router. In contrast to Routing Information Base, orrouting tables, FIBs are

optimized for fast lookup of destination addresses, while RIBs are optimized for

efficient updating by routing protocols and otherControl Plane methods. To forward,

the router looks up a packet's destination address in the FIB.

FIBs in Ingress Filtering against Denial of Service

FIBs also play a role in an Internet Best Current Practice of ingress filtering. In the

basic form of ingress filtering[2], if a packet arrives on an interface, the ingress

filter, in an interface-specific FIB, looks up the source address of thepacket. If the

interface has no route to the source address, the packet is assumed to be part of a

denial of service attack, using a false or spoofed source address, and the router

discards the packet.

When the router is multihomed, ingress filtering becomes more complex. There are

perfectly reasonable operational scenarios in which a packet could arrive on one

interface, but that specific interface might not have a route to the source address.

Ingress filtering for multihomed routers[3] will accept the packet if there is a route

back to its source address from any interface on the router. For this type of filtering,

the router may also maintain an adjacency table, also organized for fast lookup, that

keeps track of the router interface addresses that are on all directly connected

routers.

FIBs in Differentiated Services/Quality of Service Routing

IP Differentiated Services provides an additional method to select outgoing

interfaces, based on a field [4] that indicates the forwarding priority of the packet, as

well as the preference of the packet to be dropped in the presence of congestion.

Routers that support differentiated service not only have to look up the output

interface for the destination address, but need to send the packet to the interface that

best matches the Differentiated Services requirements. In other words, as well as

matching the destination address, the FIB has to match Differentiated Services Code

Points (DSCP).

FIB Information for Additional Processing

Specific router implementations may, when a destination address or other FIB

criterion is matched, specify other action to be done before forwarding (e.g.,

accounting or encryption), or applying an access control list that may cause the

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packet to be dropped

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Types of various series routers:

Cisco 800 Series Router

Overview

Cisco 800 Series routers are secure broadband routers extending concurrent data,

security, and wireless services to to enterprise branch officers, teleworkers and small

businesses, helping to increase productivity and streamline operations.

Specifications

Suitable for ISDN, serial connections (Frame Relay, leased lines, X.25 or

asynchronous dialup), IDSL, and ADSL connections

Enhanced Security using VPNs with integrated stateful firewall and IPSec

encryption

Cisco IOS software for lower total cost of ownership

Field-upgradable memory options to allow easy migration to the latest

networking features

New & Used Cisco 800 Series

We sell new and used Cisco 800 Series Routers and other Cisco Networks gear at

significant discounts to list prices. Our used Cisco gear is extensively tested and

subject to a minimum 24-hour burn-in to ensure reliability.

All Cisco Networks products represented by Alpha Digital come with full

warranties and are guaranteed to be eligible for the manufacturers maintenance

program.

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Overview of the 2500 series Router

lists the router models discussed in this publication and provides a summaryof the interfaces supported on each model. These router models are similarin functionality, but differ in the number of interfaces supported.

Table 1-1 Summary of Router Interfaces

ModelEthernet

AUI1(DB-15)

TokenRing (DB-

9)Serial

(DB-60)ISDN2BRI3

(RJ-45)

Cisco 2501/

CPA2501

1 - 2 -

Cisco 2502/CPA2502

- 1 2 -

Cisco 2503/CPA2503

1 - 2 1

Cisco 2504/CPA2504

- 1 2 1

Cisco 2513/CPA2513

1 1 2 -

Cisco 2514/CPA2514

2 - 2 -

Cisco 25154 - 2 2 -1AUI = attachment unit interface.

2ISDN = Integrated Services Digital Network.

3

BRI = Basic Rate Interface.4A CPA2515 model is not available.

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Note Throughout the remainder of the publication, one model number willbe used in text references. For example, references to the model 2501 routerwill apply to both the Cisco 2501 and CPA2501 routers.

Hardware Features

In addition to the interfaces listed in , the routers include the followinghardware features:

Dynamic random-access memory (DRAM) for main memory and sharedmemory

Nonvolatile random-access memory (NVRAM) for storing configurationinformation

Flash memory for running the Cisco IOS software

EIA/TIA-232 console port for local system access using a console terminal

Note EIA/TIA-232 and EIA/TIA-449 were known as recommendedstandards RS-232 and RS-449 before their acceptance as standards by theElectronic Industries Association (EIA) and Telecommunications Industry

Association (TIA).

Figure 1-1 Model 2501 Router Rear Panel

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Figure 1-2 Model 2502 Router Rear Panel

Figure 1-3 Model 2503 Router Rear Panel

Figure 1-4 Model 2504 Router Rear Panel

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Figure 1-5 Model 2513 Router Rear Panel

Figure 1-6 Model 2514 Router Rear Panel

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Figure 1-7 Model 2515 Router Rear Panel

System Specifications

The system specifications of the routers are listed in Table 1-2.

Table 1-2 System Specifications

Description Specification

Dimensions (H xW x D)

1.75 x 17.5 x 10.56 in.(4.44 x 44.45 x 26.82 cm),one rack unit

Weight 10 lb (4.5 kg)

Input voltage, ACpower supplyCurrentFrequencyPower dissipation

100 to 240 VAC1.2 to 0.6A50/60 Hz40W (maximum), 135.5 Btus1/hr

Input voltage, DCpower supply

CurrentPower dissipation

40W, 40 to 72 VDC1.5 to 1.0A

40W (maximum), 135.5 Btus/hr

Processor 20-MHz Motorola 68EC030

Interfaces See for a list of interfaces supported oneach router model.

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Ethernet AUI (IEEE2802.3) (DB-15)

Token Ring (IEEE 802.5) (DB-9)

Synchronous serial3(DB-60)

ISDN BRI (RJ-45)4

Console (RJ-45)

Auxiliary (RJ-45)

Operatingenvironment

32 to 104F (0 to 40C)

Nonoperatingtemperature

-40 to 185F (-40 to 85C)

Operatinghumidity

5 to 95%, noncondensing

Noise level 34 dBa @ 3 ft (0.914 m)

Regulatorycompliance

FCC Class A and Canadian DOC Class A

For more regulatory information, refer to

the document that accompanied yourrouter.

Cisco 2600 Series Modular Access Router

Cisco Systems Extends Enterprise-Class Versatility, Integration, and Power to

Remote Branch Offices with the Cisco 2600 Series Modular Access Router

Family.

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The Cisco 2600 series shares modular interfaces with the Cisco 1600 and 3600

series, providing a cost-effective solution to meet today's remote branch office needs

for applications such as:

Secure Internet/intranet access with optional Firewall

Multiservice voice/data integration

Analog and digital dial access services

Virtual Private Network (VPN) access

Virtual LANs (VLANs)

The modular architecture of the Cisco 2600 series allows interfaces to be upgraded

to accommodate network expansion or changes in technology as new services and

applications are deployed. By integrating the functions of multiple separate devices

into a single, compact unit, the Cisco 2600 series reduces the complexity of

managing the remote network solution. Driven by a powerful RISC processor, theCisco 2600 series provides the extra power needed to support the advanced quality

of service (QoS) and security features required in today's remote branch offices.

The Cisco 2600 series is available in six base configurations:

Cisco 2610---One Ethernet port

Cisco 2611---Two Ethernet ports

Cisco 2612---One Ethernet port, one Token Ring port

Cisco 2613---One Token Ring port

Cisco 2620---One autosensing 10/100 Mbps Ethernet port Cisco 2621---Two autosensing 10/100 Mbps Ethernet ports

Each model also has two WAN Interface Card (WIC) slots, one Network Module

slot, and an Advanced Integration Module (AIM) slot.

The WAN interface cards available for the Cisco 1600, 1720, 2600, and 3600 routers

support a variety of serial, Integrated Services Digital Network Basic Rate Interface

(ISDN BRI), and integrated channel service unit/data service unit (CSU/DSU)

options for primary and backup WAN connectivity. Network modules available for

the Cisco 2600 and 3600 series support a broad range of applications, includingmultiservice voice/data integration, analog and ISDN dial access, and serial device

concentration. The internal Data Compression Advanced Integration Module for the

Cisco 2600 series off-loads the task of performing high-speed data compression.

From the 2600's main CPU, allowing compressed data throughput of up to 8-Mbps

while preserving external interface slots for other applications.

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Figure 1: Cisco 2600 Series Modular Access RoutersKey Benefits

The Cisco 2600 series supports the value of end-to-end Cisco network solutions with

the following benefits:

Inv estment protection ---Because the Cisco

2600 series supports field-upgradable modular components, customers can

easily change network interfaces without a "forklift upgrade" of the entire

branch office network solution. The AIM slot of the Cisco 2600 platform

further protects investments by offering the expandability to support advanced

services such as hardware-assisted data compression and, in the future

hardware-assisted data encryption.

Lower cost of ownership---By integrating the functions of CSU/DSUs, ISDN

Network Termination (NT1) devices, firewall modems, compression or

encryption devices, and other equipment found in branch office wiring closetsin a single, compact unit, the Cisco 2600 series provides a space-saving

solution that can be managed remotely using network management

applications such as CiscoWorks and CiscoView.

Multiservice voice/data integration---The Cisco 2600 series reinforces

Cisco's commitment to integrate multiservice voice/data integration

capabilities to its product portfolio, allowing network managers to save long-

distance interoffice calling costs and enabling next-generation voice-enabled

applications such as integrated messaging and Web-based call centers. Using

the Voice/Fax modules, the Cisco 2600 may be deployed in both Voice over IP

(VoIP) and Voice over Frame Relay (VoFR) networks.

Part of a Cisco end-to-end solution---As part of Cisco's comprehensive end-

to-end networking solution, the Cisco 2600 series allows businesses to extend

a cost-effective, seamless network infrastructure to the branch office.

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Key Features and Benefits:

The Cisco 2600 series brings a cost-effective combination of versatility, integration,

and power to remote branch offices with the key features listed in Table 1.

Table 1 Key Features and

Benefits of the Cisco 2600

SeriesFeatures

Benefits

Versatility and Investment

Protection

Modular Architecture

Network interfaces are field-upgradable toaccommodate future technologies while

providing a solution to meet today's needs

Additional interfaces can be added on a "pay as

you grow" basis to accommodate network

growth

LAN and WAN interface configuration is

easily customized for individual needs

WAN Interface Cards andNetwork Modules Shared

with Cisco 1600, 1700, and

3600 Series Routers

Reduced cost of maintaining inventory ofCisco 1600, 1700, 2600, and 3600 series

modular components

Lower training costs for support personnel

Advanced Integration

Module Slot

Expandability for integration of advanced high

performance services such as hardware-

assisted data compression or encryption

DC Power Supply Option Allows deployment in DC power environments

such as telecommunications carrier central

offices

Enterprise-Class

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Performance

High-Performance RISC

Architecture

Support for advanced QoS features such as the

Resource Reservation Protocol (RSVP),

Weighted Fair Queuing (WFQ), and IPPrecedence to reduce recurring WAN costs

Enables security features such as data

encryption, tunneling, and user authentication

and authorization for VPN access

ICSA-certified Cisco IOS Firewall feature sets

provide support for advanced security features

such as Context-Based Access Control

(CBAC), Java blocking, denial of service

protection, and audit trails Support for cost-effective, software-based data

compression and data encryption

Integration of legacy networks via data link

switching plus (DLSW+) and Advanced Peer-

to-Peer Networking (APPN)

High-speed routing performance of up to

25,000 packets per second for maximum

scalability

Full Cisco IOS Software

Support

Supports the same IOS software Feature Sets

as the Cisco 2500 and 3600 series

Simplified Management

Integrated CSU/DSU,

Analog Modem and NT1

Options

Enables remote management of all Customer

Premise Equipment (CPE) elements for higher

network availability and lower operational

costs

Support for CiscoWorks and

CiscoView

Allows simplified management of all

integrated and stackable components

Support for Cisco Voice Reduces the cost of deploying and managing

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Manager (CVM) integrated voice/data solutions

Enhanced Setup Feature Context-sensitive questions guide the user

through the router configuration process,

allowing faster deployment

Support for Cisco AutoInstall Configures remote routers automatically across

a WAN connection to save cost of sending

technical staff to the remote site

Part of Cisco's Enterprise

Stackable Solutions

Can be stacked with LAN switches such as the

Catalyst 1900 or 2820XL for simplified

management

VLAN Support Enables inter-VLAN routing via Cisco's Inter-

Switch Link (ISL) protocol (Cisco 2620 and

2621)

Reliability

Redundant Power Supply

Option

RPS can be shared with other network

components such as the Cisco Catalyst 1900

series to protect the network from downtimedue to power failures

Dial-on-Demand Routing Allows automatic backup of WAN connection

in case of a primary link failure

Dual Bank Flash Memory Backup copy of the Cisco IOS software can be

stored in Flash memory

Ergonomic Design

LED Status Indicators Provide at-a-glance indications for power, RPS

status, network activity, and interface status

All Network Interfaces Simplifies installation and cable management

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Located on Back of Unit for maximum uptime

Easy-to-Open Chassis

Design

Allows fast and easy access for installation of

memory or AIM

Multispeed Fan Enables quiet operation in office environments

Figure 2: Cisco 2600 Series Back Panel View (Cisco 2611 shown)

Hardware/Software Options

Cisco 2600 series routers offer a choice of Ethernet, Token Ring, and autosensing

10/100 Ethernet LAN interfaces. In addition, each model features two WAN

Interface Card (WIC) slots, one Network Module slot, and an Advanced Integration

Module (AIM) slot.

WAN Interface Card Options:

The Cisco 2600 series supports all WAN Interface Cards available for the Cisco

1600, 1700 and 3600 series, as well as two new dual-port serial WAN interface cards

to maximize interface density and slot efficiency. The new dual-serial port WAN

interface cards feature Cisco's new, compact, high-density Smart Serial connector to

support a wide variety of electrical interfaces when used with the appropriate

transition cable.

Figure 3: Dual-Port High-Speed Serial WIC (up to 4 Mbps/port)

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Figure 4: Dual-Port Async/Sync Serial WIC (up to 128 Kbps/port)

Table 2 WAN Interface Cards and Voice Interface Cards for Cisco 2600 Series

Part Number Description

WIC-1DSU-T1 T1/Fractional T1 CSU/DSU (requires IOS software version

11.3(4)T or later)

WIC-1DSU-

56K4

One-port four-wire 56/64-kbps CSU/DSU

WIC-1T One-port high-speed serial

WIC 2T Dual high-speed serial

WIC-2A/S Two-port async/sync serial

WIC-1B-S/T One-port ISDN BRI

WIC-1B-U One-port ISDN BRI with NT1

Network Module Options

The Cisco 2600 series supports the Network Modules listed in Table 3; these

modules are shared with the Cisco 3600 series.

Table 3 Network Modules for

Cisco 2600 SeriesModule

Description

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Serial Network Modules for Cisco 2600 series (requires IOS software release

11.3(2) or later)

NM-16A 16-port high density async network modu

NM-32A 32-port high density async network modu

NM-4A/S Four-port low speed (128 Kbps max)

async/sync serial network module

NM-8A/S Eight-port low speed (128 Kbps max)

async/sync serial network module

LAN Network Modules for Cisco 2600 series (requires IOS software release11.3(4)T or later)

NM-1E One-port Ethernet network module

NM-4E Four-port Ethernet network module

NM-1ATM-251 One-port ATM 25Mbps network module

Dial, ISDN and Channelized Serial Network Modules for Cisco 2600 series(requires IOS software release 11.3(4)T or later)

NM-1CT1 One-port channelized T1/ISDN PRI network

module

NM-1CT1-CSU One-port channelized T1/ISDN PRI with

CSU network module

NM-2CT1 Two-port channelized T1/ISDN PRI netwmodule

NM-2CT1-CSU Two-port channelized T1/ISDN PRI with

CSU network module

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NM-1CE1B One-port channelized E1/ISDN PRI balan

network module

NM-1CE1U One-port channelized E1/ISDN PRI

unbalanced network module

NM-2CE1B Two-port channelized E1/ISDN PRI balan

network module

NM-2CE1U Two-port channelized E1/ISDN PRI

unbalanced network module

NM-4B-S/T Four-port ISDN BRI network module (S/T

interface)

NM-4B-U Four-port ISDN BRI with NT-1 network

module (U interface)

NM-8B-S/T Eight-port ISDN BRI network module (S/T

interface)

NM-8B-U Eight-port ISDN BRI with NT-1 network

module (U interface)

NM-8AM Eight analog modem network module

NM-16AM Sixteen analog modem network module

Voice/Fax Network Modules for Cisco 2600 series (requires IOS release 11.3(2) or

later)

Voice/Fax Network Modules for Cisco 2600 series (requires IOS release 11.3(2) orlater)

NM-1V1 One-slot voice/fax network module (up to 2

voice channels)

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NM-2V1 Two-slot voice/fax network module (up to 4

voice channels)

1The voice/fax and ATM-25 network modules require a Cisco IOS Plus feature set.

Advanced Integration Module Options

Table 4 Voice Interface Cards for use

with the Voice/Fax Network Modules

Module

Description

VIC-2FXS Two-port FXS voice/fax interface card for

voice/fax network module

VIC-2FXO Two-port FXO voice/fax interface card for

voice/fax network module

VIC-2FXO-EU Two-port FXO voice/fax interface card for

Europe

VIC-2FXO-M3 Two-port FXO voice/fax interface card for

Australia

VIC-2E/M Two-port E&M voice/fax interface card for

voice/fax network module

VIC-2BRI-S/T-TE1 Two-port BRI S/T terminal equipment

voice/fax interface card for voice/fax

network module

1

Supported on the Cisco 261x with Cisco IOS 12.0(2)XD and Cisco 262x on12.0(3)T or later

The Data Compression AIM is the first product to take advantage of the Cisco 2600's

internal Advanced Integration Module slot, ensuring that external slots remain

available for components such as integrated CSU/DSUs, analog modems, or

Voice/Fax Network Modules. The Data Compression AIM for the Cisco 2600 series

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delivers a cost-effective option for reducing recurring WAN costs and maximizing

the benefit of the advanced bandwidth management features of the Cisco IOS

software.

Table 5 Advanced Integration Module for the Cisco 2600 Series

Module Description

AIM-

COMPR2

Data Compression AIM for the Cisco 2600 series (requires IOS

software release 12.0(2) or later)

Table 6 Cisco IOS Software Feature Sets and Memory Requirements for Cisco

2600 Series IOS release 12.0(2)

IP IP/IPX/AT/D

EC

Remote

Access Servi

ces

Enterpri

se

Enterpris

e/ APPN

Base Feature

Set

4-MB

Flash

20-

MB

DRA

M

8-MB Flash

20-MB DRAM

4-MB Flash

20-MB

DRAM

--- ---

Firewall only

no encryption

4-MB

Flash

20-

MBDRA

M

--- --- --- ---

Plus Feature

Sets

8-MB 8-MB Flash --- 8-MB 8-MB

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Flash

24-

MB

DRAM

24-MB DRAMFlash

32-MB

DRAM

Flash

32-MB

DRAM

Firewall and

Plus Feature

Sets

--- 8-MB Flash

24-MB DRAM

--- --- ---

Plus 40 with

Plus features

and 40-bit encryption

8-MB

Flash

32-

MB

DRA

M

--- --- --- ---

Plus IPSec 56

with Plus

features and

56-bit IPSec

encryption

8-MB

Flash

24-

MBDRA

M

--- --- 8-MB

Flash

32-MB

DRAM

8-MB

Flash

32-MB

DRAM

Plus IPSec

3DES with

Plus features

and triple

DES 56 bit

IPSecencryption

8-MB

Flash

24-

MB

DRA

M

--- --- 8-MB

Flash

32-MB

DRAM

8-MB

Flash

32-MB

DRAM

Firewall Plus

IPSec 56

Feature Set

8-MB

Flash

24-

--- --- 8-MB

Flash

32-MB

---

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with Firewall,

Plus features

and 56-bit

IPSec encrypt

ion

MB

DRA

M

DRAM

Firewall Plus

IPSec 56 with

Firewall, Plus

features and

triple 56 bit

IPSec

encryption

8-MB

Flash

24-

MB

DRA

M

--- --- 8-MB

Flash

32-MB

DRAM

---

Cisco IOS Software:

With support for the full range of available Cisco IOS feature sets, the Cisco 2600

series supports the broadest range of network services in the industry. Base feature

sets support popular protocols and standards such as NAT, OSPF, Border Gateway

Protocol (BGP), Remote Access Dial-In User Service (RADIUS), IP Multicast,

RMON, and WAN optimization features (such as Bandwidth on Demand; Custom,Priority and Weighted Fair Queuing, Dial Back-up and RSVP). "Plus" feature sets

contain an additional number of value-added features such as legacy mainframe

protocols, DLSw, L2TP, L2F, Voice/Data integration, Asynchronous Transfer Mode

(ATM), VLANs, Netflow, etc. Additional feature sets include IPSec, and 3DES

encryption as well as ICSA certified Firewall capabilities.

The Cisco 2600 series supports Cisco IOS Release 11.3(2) and later. A detailed

listing of Cisco IOS feature set content can be found in the Cisco 2600 IOS release

notes as well as in the Cisco 2600 software features and memory requirements

product bulletin.

Technical Specifications

Processor: Motorola MPC860 40 MHz (Cisco 261X), Motorola MPC860 50

MHz (Cisco 262x)

Flash Memory: 4 to 16 MB (32MB max. on Cisco 262x)

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System Memory (DRAM): 24 to 64 MB

WAN Interface Card Slots: 2

Network Module Slot: 1

AIM Slot: 1

Console/Aux Speed: 115.2-Kbps (maximum)

Width: 17.5 in. (44.5 cm)

Height: 1.69 in. (4.3 cm)

Depth: 11.8 in. (30 cm)

Weight (min): 8.85 lb. (4.02 kg)

Weight (max): 10.25 lb. (4.66 kg)

Power Dissipation: 72W (maximum)

AC Input Voltage: 100 to 240 VAC

Frequency: 47 to 64 Hz

AC Input Current: 1.5 amps

DC Input Voltage: -38V to -75V DC Input Current: 2 amps

Operating Temperature: 32 to 104 F (0 to 40 C)

Non-operating Temperature: -13 to 158 F (-25 to 70 C)

Relative Humidity: 5 to 95% non-condensing

Noise Level (min): 38-dbA

Noise Level (max): 42-dbA

The Cisco 2600 series conforms to a number of safety, EMI, immunity and network

homologation standards. Details can be obtained through your Cisco reseller or

account manager.

Description

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Nortel VPNRouter 1700Series

Request aquick quote forthe:Nortel VPN

Router 1700

Series

Nortel

Routers

AviciSystemsCore Routers

NortelAccess StackNode (ASN)

NortelAdvancedRemote

Node (ARN) Nortel

BackboneConcentratorNode (BCN)

NortelBackboneLink Node(BLN)

NortelEthernetRoutingSwitch 5520

NortelMultiprotocolRouter 2430

Nortel

The Nortel VPN Router 1700 Series isavailable from NexStor. NexStoroffers the most competitive prices forNortel products.

Nortel VPN Router 1700 Series

Nortel VPN Router 1700 Series servesseveral roles in enterprise and carrierIP networks: basic IP access router,dedicated VPN switch, or firewall --and evolve from one to anothersimply by licensing a software key.Supporting up to 500 tunnels, VPNRouter 1700 are ideal for officecentres, campuses, or large branch

offices with several hundred users.

The VPN Router 1700 Series are

available in two models:

The VPN Router 1700 is a fullyfeatured platform with a singlehardware expansion slot. Itaddresses sites with limited need

for optional LAN, WAN or hardwareacceleration cards.

The VPN Router 1740, with up tofour expansion slots, can integratea range of LAN, WAN andacceleration cards for fan-out andback-up purposes. It provides

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