TDC 365-98-901, Spring 2002 2-1

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

TDC 365-98-901, Spring 2002 2-2

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

TDC 365-98-901, Spring 2002 2-3

Direct broadcast address

TDC 365-98-901, Spring 2002 2-4

Limited broadcast address

TDC 365-98-901, Spring 2002 2-5

“this” host on “this” network address

Provide initial configuration information

TDC 365-98-901, Spring 2002 2-6

Specific host on this network

TDC 365-98-901, Spring 2002 2-7

Loopback address

TDC 365-98-901, Spring 2002 2-8

Figure 5-2 subnetting

TDC 365-98-901, Spring 2002 2-9

TDC 365-98-901, Spring 2002 2-10

Subnet mask

TDC 365-98-901, Spring 2002 2-11

Logical AND

TDC 365-98-901, Spring 2002 2-12

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

TDC 365-98-901, Spring 2002 2-13

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

TDC 365-98-901, Spring 2002 2-14

Range of addresses in the example

TDC 365-98-901, Spring 2002 2-15

Subnetworks in the example

TDC 365-98-901, Spring 2002 2-16

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

TDC 365-98-901, Spring 2002 2-17

Supernetwork

TDC 365-98-901, Spring 2002 2-18

Supernet mask

TDC 365-98-901, Spring 2002 2-19

Two ways of defining a supernet

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

TDC 365-98-901, Spring 2002 2-20

Classless Interdomain Routing (CIDR)

TDC 365-98-901, Spring 2002 2-21

Direct and Indirect delivery

Same network/subnet/ supernet address

TDC 365-98-901, Spring 2002 2-22

Next-hop routing

TDC 365-98-901, Spring 2002 2-23

Network-specific routing

TDC 365-98-901, Spring 2002 2-24

Host-specific routing

TDC 365-98-901, Spring 2002 2-25

Default routing

TDC 365-98-901, Spring 2002 2-26

Routing module and routing table

Fields in routing table

Routing tables: static v.s. dynamic

TDC 365-98-901, Spring 2002 2-27

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

TDC 365-98-901, Spring 2002 2-28

An example network.

TDC 365-98-901, Spring 2002 2-29

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