Routing

gascitytankΔίκτυα και Επικοινωνίες

28 Οκτ 2013 (πριν από 3 χρόνια και 5 μήνες)

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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 other


Timeouts are common while routers
add to cache


Then, 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 t

2.
RouterA(config)#
router rip

3.
RouterA(config
-
router)#
network 10.0.0.0

4.
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