View
233
Download
0
Tags:
Embed Size (px)
Citation preview
Chapter 5
IP Routing
Routing
Sending packets through network from one device to another
What must routers know?– Destination address– Neighboring routers– Possible routes to remote network– Best route to remote network– How to keep routing information current
IP Routing Process
Pages 207-210 shows steps when Host A pings Host B (lots of steps!)
IP Routing Process (cont.)
IP Routing Process (cont.)
IP Routing in Larger Network
Figure 5.2 shows diagram of network Table 5.1 shows networks, interfaces, and
addresses Then, configure those routers!
IP Routing in Our Network
Routing tables keep track of networks If destination is not in routing table, packet is
dropped! Must build routing table and keep it current Types of routing
– Static– Default– Dynamic
Static Routing
Admin manually adds routes to tables No overhead on router CPU, no overhead traffic
between routers, very secure Big pain to add routes often, not good for large or
changing networks Adding a static route:
ip route [destination_network] [mask] [next_hop_address or exitinterface] [administrative_distance] [permanent]
Verify Your Routing
Ping from one end router to the otherTimeouts are common while routers
add to cacheThen, connectivity should be quick
Default Routing
Only one exit port out of a stub network? Can set a default route
Routers Lab_A and Lab_C qualify Need to remove static routes and add one
default route
Dynamic Routing
Use protocols to automatically update tables Types of routing protocols for Ch. 5:
– Routing Information Protocol (RIP)– Interior Gateway Routing Protocol (IGRP)
Advanced protocols not covered here:– Enhanced Interior Gateway Routing Protocol
(EIGRP)– Open Shortest Path First (OSPF)
Administrative Distances
Rate the trustworthiness of routes
Classes of Routing Protocols
1. Distance Vector– Distance is hops to remote network– Vector is direction to remote network– Used by RIP and IGRP
2. Link State and Hybrid– Keeps track of directly attached neighbors,
topology of entire network, builds routing tables– OSPF and EIGRP (not covered yet)
Distance-Vector Routing
Do you know where RIP has problems?
Distance-Vector Start-up
Distance Vector Convergence
Routing Loops
What if Network 5 goes down? Routing tables don’t converge quickly, loops
can occur between remote sites
Stopping Routing Loops
Maximum hop count – avoids routers sending packets infinite times
Split Horizon – routing info cannot be sent back to where it was received
Route Poisoning – send immediate message that route is down (don’t wait for normal routing broadcast timer)
Holddowns – wait longer than normal before announcing that route is back up
RIP
A true distance-vector protocol– Sends updates every 30 seconds on all active
interfaces– Only uses hop count
Maximum allowable hop count of 15
Good for small networks– Inefficient on large networks or slow WAN links– RIP v1 requires same subnet mask for all devices
RIP
RIP Timers– Route update timer – usually 30 seconds– Route invalid timer – no message from router for 90
seconds? Route marked as invalid– Route flush timer – 240 seconds and still no word?
Remove route from table
Configure RIP
First, remove any static routes. Then,
1. Lab_A(config)# router rip
2. Lab_A(config)# network 192.168.10.0
3. Lab_A(config)# network 192.168.20.0
4. Lab_A(config)# ^Z
5. Lab_A#
More RIP Stuff
Verifying the RIP Routing Tables– 2621A(config)#sh ip route
You don’t want RIP broadcast to Internet– Holding Down RIP Propagation
1. RouterA#config t2. RouterA(config)#router rip3. RouterA(config-router)#network 10.0.0.04. RouterA(config-router)#passive-interface serial 0
Interior Gateway Routing Protocol (IGRP)
Cisco-only protocol for larger networks Max hop count of up to 255 Looks at hop count, bandwidth, and delays IGRP timers work on larger networks
– Update timers – 90 seconds– Invalid timers – 270 seconds– Holddown timers – 280 seconds– Flush timers – 630 seconds
Configure and Verify IGRP
Use same number for routers on same network IGRP Routing (e.g. 10)
Lab_A(config)#router igrp 10
Lab_A(config-router)#network 192.168.10.0
Check configurations (pp. 239-245)show ip route
show protocols
show ip protocol
debug ip rip
debug ip igrp events
debug ip igrp transactions