The Internet Control Message Protocol (ICMP) is one of the core protocols of the Internet protocol suite. It is chiefly used by networked computers'

The Internet Control Message Protocol (ICMP) is one of the core protocols of the Internet protocol suite. It is chiefly used by networked computers' operating systems to send error messages—indicating, for instance, that a requested service is not available or that a host or router could not be reached.

ICMP differs in purpose from TCP and UDP in that it is usually not used directly by user network applications.

One exception is the ping tool, which sends ICMP Echo Request messages (and receives Echo Response messages) to determine whether a host is reachable and how long packets take to get to and from that host.

RFC 792 (get it and study it) ICMP message is constructed and then passed

down to IP layer, usually from a normal IP datagram that has generated an ICMP response.

ICMP provides a means for transferring messages from routers and other host to a host.

E.g when a datagram cannot reach its destination, when the router does not have the buffering capacity to forward a datagram, and when the router can direct the station to send traffic on a shorter route

An ICMP message starts with a 64-bit header consisting of the following:

Type (8 bits): Specifies the type of ICMP message

Code (8 bits): used to specify parameters of the message that

can be encoded in one or a few bits Checksum: (16 bits):

checksum of the entire ICMP message. This is the same checksum algorithm used for IP

Parameters (32 bits): used to specify more lengthy parameters

Destination unreachable A router may return this message if it does not

know how to reach the destination network Time exceeded

Message if the lifetime of the datagram expires, a host it cannot complete reassembly within the time limit

Parameter problem A semantic error in an IP header

Source quench Message provides a rudimentary form of flow

control

Redirect A message to a host on a directly connected router to

advise the host of a better route to a particular destination

Echo and echo reply Messages provide a mechanism for testing that

communication is possible between entities Timestamp and timestamp reply

Messages provide a mechanism for sampling the delay characteristic of the internet

Address mask request and address mask reply The address mask request and reply messages allow a

host to learn the address mask for the LAN to which it connects

IP v 1-3 defined and replaced IP v4 - current version IP v5 - streams protocol IP v6 - replacement for IP v4

During development it was called IPng Next Generation

The decision to standardize on a 32 bit address space meant that there were only 232 (4,294,967,296) IPv4 addresses available.

During the early days of the Internet, the seemingly unlimited address space allowed IP addresses to be allocated based on requests rather than its actual need.

Over the next few years, conventional computers will be joined by Personal Digital Assistants, Mobile Phones with data processing capability, smart set-up boxes with integrated web browsers, and from copy machines to kitchen appliances.

Class C, which supports 254 hosts, is too small. Class B, which supports 65534 hosts is too large. In the past, sites with several hundred hosts

have been assigned as single Class B address rather than couple of Class C addresses.

Unfortunately, this has resulted in a premature depletion of the Class B network address space.

Subnetting - In 1985, RFC 950 defined a standard procedure to

support the subnetting, or division, of a single Class A, B, or C network number into smaller pieces.

Internet routers use only the network-prefix of the address to route traffic to a subnetted environment.

Routers within the subnetted environment use the extended-network-prefix to route traffic between the individual subnet.

CIDR was officially documented in September 1993 in RFC 1517, 1518, 1519, 1520

Eliminates the traditional concept of Class A, B and C networks and replaces it with concept of “network prefix”

CIDR supports the deployment of arbitrary size networks rather than the standard 8-bit, 16-bit, or 24 bit network numbers associated with classful addressing.

Good News - CIDR is working. Bad News - Recent growth trends indicate

that the number of Internet routes is beginning to increase at an exponential rate.

1752 - Recommendations for the IP Next Generation Protocol

2460 - Overall specification 2373 - addressing structure others (find them) www.rfc-editor.org

Expanded address space 128 bit addresses instead of 32-bit addresses of IPv4.

This is an increase of address space by a factor of 296 . This allows on the order of 6 x 1023 unique addresses per square meter of the surface of the earth.

Improved option mechanism Separate optional headers between IPv6 header and

transport layer header Most are not examined by intermediate routes

▪ Improved speed and simplified router processing▪ Easier to add additional options

Address autoconfiguration This capability provides for dynamic assignment of

IPv6 addresses

Increased addressing flexibility Anycast - delivered to one of a set of nodes Improved scalability of multicast addresses

Support for resource allocation Replaces type of service field in IPv4 Labeling of packets to particular traffic flow Sender requests special handling e.g. real time video

Example:

FEDC:BA98:7654:3210:FEDC:BA98:7664:3210

128 bit is represented as: 8 integers (16-bit) separated by colons

▪ each integer is represented by 4 hex digits

Skip leading zeros Example:1080:0000:0000:0000:0008:0800:200C:

417A is reduced to: 1080:0:0:0:8:800:200C:417A

A set of consecutive nulls is replaced by :: (at most one :: inside an address)

the above address is reduced to:▪ 1080::8:800:200C:417A

128 bits long Three types of address

Unicast addresses: An identifier for a single interface. A packet sent to a unicast address is delivered to the interface identified by that address

Anycast addresses: An identifier for a set of interfaces (typically belonging to different nodes). A packet sent to an anycast address is delivered to one of the interfaces (the “nearest” one) identified by that address

Multicast: An identifier for a set of interfaces (typically belonging to different nodes). A packet sent to mulitcast address is delivered to all interfaces identified by that address.

V6: 6 fields + 2 addr V4: 10 fields + 2 addr + options Deleted:

▪ Header length ▪ type of service▪ identification, flags, fragment offset▪ Header Checksum

Added:▪ Priority▪ Flow label

Renamed:▪ length -> Payload length▪ Protocol -> Next header▪ time to live -> Hop Limit

Redefined: Option mechanism

Hop-by-Hop Options Require processing at each router

Routing Similar to v4 source routing

Fragment Authentication Encapsulating security payload Destination options

For destination node

Version (4 bits): Internet protocol version number; the value is 6.

DS/ECN (8 bits): used by originating nodes and/or forwarding routers for differentiated services and congestion functions, see IPv4 DS/ECN field.

Flow Label (20 bits): used by a host to label those packets for which it is requesting special handling by routers within a network.

Payload Length (16 bits): Length of the remainder of the IPv6 packet following the header, in octets. In other words, this is the total length of all of the extension headers plus the transport-level PDU.

Next Header (8 bits): Identifies the type of header immediately following the IPv6 header; this will either be an IPv6 extension header or a higher-layer header, such as TCP or UDP.

Hop Limit (8 bits): The remaining number of allowable hops for this packet. The hop limit is set to some desired maximum value by the source and decremented by 1 by each node that forwards the packet. The packet is discarded if Hop Limit is decremented to zero.

Source Address (128 bits): address of originator of the packet.

Destination Address (128 bits): address of intended recipient of the packet.

Although the IPv6 header is longer than the mandatory portion of the IPv4 header (40 octets versus 20 octets), it contains fewer fields (8 versus 12). Thus, routers have less processing to do per header, which should speed up routing.

Next header Identifies the type of header immediately following

this header Header extension length

Length of this header in 64-bit units Options

A variable length field consisting of one or more option definitions

Fragmentation only allowed at source No fragmentation at intermediate routers Node must perform path discovery to find

smallest MTU of intermediate networks Source fragments to match MTU Otherwise source limit all packets to 1280

octets which is the minimum MTU that must be supported by each network

Next Header (8 bits) Identifies the type of header immediately

following this header Reserved (8 bits) for future use Fragmentation offset (13 bits)

Indicates where in the original packets the payload of this fragment belongs

Reserved (2 bits) reserved for future use More flag (1 bit)

1= more fragments, 0= last fragment Identification(32 bits)

List of one or more intermediate nodes to be visited

Next Header Identifies the type of header immediately following this

header Header extension length

Length of this header in 64-bit units Routing type

Identifies a particular routing header variant. If a router does not recognize the routing type value, it must discard the packet

Segments left i.e. number of route segments remaining, nodes still to

be visited

carries optional info for destination node Same format as Hop-by-Hop options

header

Stallings chapter 18 All RFCs mentioned plus any others

connected with these topics www.rfc-editor.org

Loads of Web sites on TCP/IP and IP version 6

basic protocol functions internetworking principles connectionless internetworking IP ICMP IPv6