IP Routing

Static Routing

2003-2004 - Information management2Groep T Leuven – Information department2/14

The Router• Router Interface is a physical connector that

enables a router to send or receive packets• Each interface connects to a separate network• Consist of socket or jack found on the outside

of a router • Types of router interfaces:

– -Ethernet– -Fastethernet– -Serial– -DSL– -ISDN– -Cable

2003-2004 - Information management3Groep T Leuven – Information department3/14

Routing Table• Routing table should contain at least 2 items

– Destination address– Pointer to the destination

Network 10.1.1.0 is missing !

2003-2004 - Information management4Groep T Leuven – Information department4/14

Routing TableRouter3#show ip routeCodes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route

Gateway of last resort is not set

10.0.0.0/24 is subnetted, 7 subnetsS 10.1.1.0 [1/0] via 10.1.4.1S 10.1.2.0 [1/0] via 10.1.4.1S 10.1.3.0 [1/0] via 10.1.4.1C 10.1.4.0 is directly connected, Serial2/0C 10.1.5.0 is directly connected, FastEthernet0/0C 10.1.6.0 is directly connected, Serial3/0S 10.1.7.0 [1/0] via 10.1.6.2Router3#

2003-2004 - Information management5Groep T Leuven – Information department5/14

Routing order1. Check for a connected network2. Search for a matching host route3. Search for a matching network route4. Search for a default gateway (last resort)

2003-2004 - Information management6Groep T Leuven – Information department6/14

The router• As a packet travels from one networking device to

another– -The Source and Destination IP addresses NEVER

change– -The Source & Destination MAC addresses

CHANGE as packet is forwarded from one router to the next.

– -TTL field decrement by one until a value of zero is reached at which point router discards packet (prevents packets from endlessly traversing the network)

2003-2004 - Information management7Groep T Leuven – Information department7/14

Router Path – step 1• PC1 Wants to send something to PC 2 here is

part of what happens – Step 1 - PC1 encapsulates packet into a

frame. Frame contains R1’s destination MAC address

2003-2004 - Information management8Groep T Leuven – Information department8/14

Router Path – step 2Step 2 - R1 receives Ethernet frame.

2003-2004 - Information management9Groep T Leuven – Information department9/14

Router Path – step 2– Step 2 - R1 receives Ethernet frame.

R1 sees that destination MAC address matches its own MAC.

R1 then strips off Ethernet frame. R1 Examines destination IP. R1 consults routing table looking for

destination IP. After finding destination IP in routing

table, R1 now looks up next hop IP address. R1 re-encapsulates IP packet with a new

Ethernet frame. R1 forwards Ethernet packet out Fa0/1

interface.

2003-2004 - Information management10Groep T Leuven – Information department10/14

Router Path – step 3Step 3 - Packet arrives at R2

R2 receives Ethernet frame R2 sees that destination MAC address matches its

own MAC R2 then strips off Ethernet frame R2 Examines destination IP R2 consults routing table looking for destination IP After finding destination IP in routing table, R2

now looks up next hop IP address R2 re-encapsulates IP packet with a new data link

frame R2 forwards Ethernet packet out S0/0 interface

2003-2004 - Information management11Groep T Leuven – Information department11/14

Router Path – step 4Step 4 - Packet arrives at R3

R3 receives PPP frame R3 then strips off PPP frame R3 Examines destination IP R3 consults routing table looking for destination IP After finding destination IP in routing table, R3 is

directly connected to destination via its fast Ethernet interface

R3 re-encapsulates IP packet with a new Ethernet frame

R3 forwards Ethernet packet out Fa0/0 interfaceStep 5 - IP packet arrives at PC2.

Frame is decapsulated & processed by upper layer protocols.

2003-2004 - Information management12Groep T Leuven – Information department12/14

Demo – packet tracer

2003-2004 - Information management13Groep T Leuven – Information department13/14

Case studies• Summary routes• Default routes• Alternative routes• Floating static• Load sharing• Trouble shooting static routes

2003-2004 - Information management14Groep T Leuven – Information department14/14

Exercise• Configure the routing that all traffic goes clock wise

10.1.0.0/24

10.5.0.0/2410.2.0.0/24

10.3.0.0/24

10.4.0.0/24

10.6.0.0/24

10.7.0.0/24

64 kbps

128 kbps

16 kbps

.1

.1

.1

.1

.2

.2

.2

.2

.1

.1

.1

.2