unit 2: ip addressing (contd.). delivery and routing of packets

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Unit 2: IP addressing (Contd.). Delivery and routing of packets

• Special IP addresses

• Private networks: 10.0.0, 172.16-172.31, 192.68.0-192.68.255

• Subnetting and subnet masks

• Supernetting and CIDR (Classless Interdomain Routing)

• Delivery and routing of packets– Routing table organizations

– Dynamic v.s. static routing

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Network addresses: Network ID + All 0’s hostid is commonly referred to as a network address

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Direct broadcast address

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Limited broadcast address

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“this” host on “this” network address

Provide initial configuration information

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Specific host on this network

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Loopback address

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Figure 5-2 subnetting

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Subnet mask

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Logical AND

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Special addresses in subnetting

These can never be assigned to a host

Restrictions can be relaxed so that these numbers may be assigned to subnets

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Example: An organization with a class B address needs at least 12 subnetworks.

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Range of addresses in the example

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Subnetworks in the example

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255.255.255.192 = 11111111 11111111 11111111 11000000 so the first mask uses the first 2 bits of the 4th byte as the subnet ID

255.255.255.224 = 11111111 11111111 11111111 11100000 so the second mask uses the first 3 bits of the 4th byte as the subnet ID

So the last byte can be 00xxxxxx, 01xxxxxx, 10xxxxxx, 11xxxxxx. 3 of these can be chosen to label the first 3 subnets. Let say we pick the first 3

01000000 = 64X.Y.Z.64

10000000 = 128X.Y.Z. 128

And the last two subnets must have 11 as the leading 2 bits in the 4th byte. The 3rd bit can varies between 0 and 1. Therefore the last two subnets have addresses of the following format in the 4th byte: 110xxxxx and 111xxxxx

11000000 = 192X.Y.Z. 192

11100000 =224X.Y.Z. 224

00000000 = 0X.Y.Z.0

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Supernetwork

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Supernet mask

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Two ways of defining a supernet

Example of supernetting. Which address belong to supernet X.Y.32.0?

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Classless Interdomain Routing (CIDR)

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Direct and Indirect delivery

Same network/subnet/ supernet address

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Next-hop routing

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Network-specific routing

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Host-specific routing

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Default routing

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Routing module and routing table

Fields in routing table

Routing tables: static v.s. dynamic

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Routing Module

Receive: an IP packet

1. For each entry in the routing table1. Apply the mask to packet destination address

2. If (the result matches the value in the destination field)1. If (the G flag is absent)

1. Use packet destination address as next hop address

2. Send packet to fragmentation module with next hop address

3. Return

2. If no match is found, send an ICMP error message

3. Return

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An example network.

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Mask Destination Next Hop F. R.C. U. I.

255.0.0.0 111.0.0.0 - U 0 0 m0

255.255.255.224 193.14.5.160 - U 0 0 m2

 255.255.255.224  193.14.5.192    U

 0

 0

 m1

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

 255.255.255.255  194.17.21.16

192.16.7.0

 111.20.18.14  UGH  0  0  m0

255.255.255.0111.15.17.32

UG 0 0 m0

255.255.255.0 194.17.21.0 111.20.18.14 UG 0 0 m0

0.0.0.0 0.0.0.0 111.30.31.8 UG 0 0 m0

Routing Table for R1 in the example