Network Layer – 2 Addressing, Subnetting Shri Mare [email protected]CSCI 367: Computer Networks I Thanks to Aran Clauson, Dustin O'Hara, Michael Meehan, Michael Tsikerdekis, Ratul Mahajan, Brian Hutchinson, and many others for sample slides and materials ...
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Thanks to Aran Clauson, Dustin O'Hara, Michael Meehan, Michael Tsikerdekis, Ratul Mahajan, Brian Hutchinson, and many others for sample slides and materials ...
Addressing Scheme• Addresses should be globally unique and should
have hierarchy.• Original addressing scheme had 3 classes, and
hence called classful addressing: Classes A, B, and C• IP address has two parts: network address and host
address.• Network address: IP address with host part as 0s.
• E.g., for class C IP address 172.16.13.42, network address is 172.16.13.0
• Nodes in the same network should have the same network address.
• Problem with classful addressing:• Address allocation is inefficient• Not enough addresses for all the devices on the
Internet!• A partial solution: subnetting
REVIEW
REVIEW
Subnetting
Subnet Mask Representation & Slash Notation• Subnet masks are commonly represented using
dotted decimal representation.• To make it easier to understand and represent
address masks, the IETF developed syntactic form that is informally known as Slash notation.
• For example• Dotted decimal: 255.255.255.0 • Slash notation: /24
Classless Addressing Scheme• Classless addressing does away with the class A, B,
and C addresses. In place of the three classes, the new scheme extends the ideas used in subnetting.
• The technology became known as Classless Inter-Domain Routing (CIDR).• Class A, B, and C, did not divide network addresses into
equal size classes. While there were fewer than seventeen thousand B class numbers created, there were more than two million C class network numbers created.
• Because C prefixes only suffice for small networks and are not amenable to subnetting, demand for C prefixes was lower
• Demand for class B prefixes address would exhaust supply
• So one of the first uses of classless addressing was known as supernetting, and would enable an organization to receive a contiguous set of class C addresses instead of a class B address.
• Natural extension of the subnet idea but to the entire IP address space.
• 5 min: Join your group and discuss the quiz questions.
• Regroup in #class
In-class activityQ1) For the IP address in slash notation 172.16.23.45/24, what is the
• Network address (in the form ww.xx.yy.zz):• Network mask (in the form ww.xx.yy.zz):
Q2) For the IP address in slash notation 172.16.23.45/25, what is the• Network address (in the form ww.xx.yy.zz):• Network mask (in the form ww.xx.yy.zz):
In-class activityQ3) A large number of consecutive IP addresses are available starting at 172.24.0.0. Suppose that an organization A requests 4096 addresses. Give the first IP address assigned, the last IP address assigned, and the network bit mask number.
• First IP address:• Last IP address:• Mask number:
• Network address:
IPv4 CIDR Blocks Reserved for Private Networks• In the context of a private intranet, that does not connect with the larger internet,
arbitrary addresses could be used. To avoid conflict between private and public addresses, the IETF reserved several address prefixes for private intranets. • Private addresses or non-routable address• If packets containing one of the private addresses is forwarded to the global internet, a
router will detect the problem and discard the packet.
Prefix Lowest address Highest address
10.0.0.0/8 10.0.0.0 10.255.255.255
172.16.0.0/12 172.16.0.0 172.31.255.255
192.168.0.0/16 192.168.0.0 192.168.255.255
169.254.0.0/16 169.254.0.0 169.254.255.255
IPv4 Special Addresses• Network Address: an address that has a Host ID of 0, is used to refer to the network itself. • Network Broadcast Address: all 1s in the Host ID of a destination address, it refers to all computers on a specific network. • Subnet Broadcast Address: using a subnet prefix of all 1s, the subnet broadcast address is used on a single network
within a site that used subnetting. • Multicast Addresses: In addition to unicast and broadcast delivery, IPv4 support multicasting (a topic we will examine in
more detail later). • Loopback Address: using the network prefix 127.0.0.0/8 (a value originally from class A range) is reserved for loopback
and intended for use in testing TCP/IP and for inter-process communication on the local computer. • All-1s: used to broadcast across local network and used at startup before a computer learns its IP address. • All-0s: Source Address: when a host need to communicate but does not know its address yet.