cisco networking academy chabot college elec 99.08 ip routing protocol highlights

CISCO NETWORKING ACADEMYCISCO NETWORKING ACADEMY

Chabot CollegeChabot College

ELEC 99.08ELEC 99.08IP Routing Protocol Highlights


IP Routing Protocol TopicsIP Routing Protocol Topics• Routing tables

• How routes are learned

• Default routes

• Metrics

• Administrative Distance

• Distance Vector / Link State

• RIP / IGRP

• Commands


Routing TableRouting Table

• Stored in RAM• Basis for all path selection decisions• Includes

destination network address - next hop pairs


Routing Table ExampleRouting Table Examplehayward#show ip routeCodes: C - connected, S - static, I - IGRP, R - RIP D - EIGRP, EX - EIGRP external, O - OSPF N1 - OSPF NSSA external type 1, N2 - OSPF NSSA E1 - OSPF external type 1, E2 - OSPF external type 2 i - IS-IS, L1 - IS-IS level-1, * - candidate default

Gateway of last resort is not set

R 192.168.4.0/24 [120/1] via 10.3.0.2, 00:00:07, Serial0 10.0.0.0/16 is subnetted, 3 subnetsC 10.2.0.0 is directly connected, Serial1C 10.3.0.0 is directly connected, Serial0R 10.1.0.0 [120/1] via 10.2.0.1, 00:00:10, Serial1R 192.168.1.0/24 [120/2] via 10.2.0.1, 00:00:10, Serial1S 192.168.2.0/24 [1/0] via 10.2.0.1C 192.168.3.0/24 is directly connected, Ethernet0


Routing Table ExampleRouting Table Examplehayward#show ip route


Destination Network Address Next Hop


How routes are learnedHow routes are learned1. Interface configuration in the config file.

Defines directly connected networks even when no dynamic routing is configured:

hayward#show ip route

10.0.0.0/16 is subnettedC 10.2.0.0 is directly connected, Serial1C 10.3.0.0 is directly connected, Serial0C 192.168.3.0/24 is directly connected, Ethernet0


How routes are learnedHow routes are learned

When dynamic routing is running, directly connected networks are listed in the routing table along with others:

hayward#show ip routeR 192.168.4.0/24 [120/1] via 10.3.0.2, 00:00:07, Serial0 10.0.0.0/16 is subnetted, 3 subnetsC 10.2.0.0 is directly connected, Serial1C 10.3.0.0 is directly connected, Serial0R 10.1.0.0 [120/1] via 10.2.0.1, 00:00:10, Serial1R 192.168.1.0/24 [120/2] via 10.2.0.1, 00:00:10, Serial1S 192.168.2.0/24 [1/0] via 10.2.0.1C 192.168.3.0/24 is directly connected, Ethernet0



2. Static routes entered manually in the router config file.




3. Routes learned from a dynamic routing protocol (e.g. RIP, IGRP, OSPF).



How routes are learnedHow routes are learned4. Default route set manually.

Shown with *

Also: gateway of last resort

oakland#show ip route Gateway of last resort is 10.2.0.1 to network 0.0.0.0

10.0.0.0/16 is subnetted, 2 subnetsC 10.2.0.0 is directly connected, Serial1R 10.1.0.0 [120/1] via 10.2.0.1, 00:00:18, Serial1R 192.168.1.0/24 [120/2] via 10.2.0.1, 00:00:18, Serial1S 192.168.2.0/24 [1/0] via 10.2.0.1C 192.168.3.0/24 is directly connected, Ethernet0R* 0.0.0.0/0 [1/0] via 10.2.0.1


Static Routes - Why?Static Routes - Why?• Security

– RIP may reveal too much of your network to others.A static route limits what you “show”.

• Backup routes– A static route can be a backup to be used automatically

if a dynamic route goes down

• Bandwidth conservation– Dynamic routing uses network bandwidth; static routes

do not. – Static routes are sufficient for stub networks


Stub NetworksStub Networks• Only one path in & out of the network;

no path selection decision:Only one path to this “stub” network

Here, there are path selection decisions.Dynamic routing needed.

A static route to the stub net

will do.


Default Routes - the ProblemDefault Routes - the Problem• For each packet, routing are decisions based on

the routing table rules. • What happens to a packet if has a destination

that is not included in the routing table?


Default Routes - the ProblemDefault Routes - the Problem• What happens to a packet sent to 209.33.45.177• It is dropped because there is no entry for that

network in the routing table:

oak#show ip routeGateway of last resort is not set



Default Routes - the ProblemDefault Routes - the Problem• But the routing table can’t hold entries for every

network, including all those on the Internet!• So we need a route for internet traffic - the

default.

If packet has a destination not on our network,try sending it here

Gateway

Our Network


Default Routes - TermsDefault Routes - Terms• default route

(through)• default gateway

(also known as)• gateway of last resort

(to)• default network


MetricMetric• Specifies the cost of a route• Dynamic routing protocol chooses the route with

the lowest cost• Metrics differ, depending on routing protocol:

Protocol Metric RIP Hop Count

(# routers packet must pass through) IGRP Default: Bandwidth, Delay

Optionally include: [Load, Reliability]


Administrative DistanceAdministrative Distance• Specifies the trustworthiness of a route source• 0 - 255 Lower values = more trustworthy• The IOS chooses the route with lowest distance:

Route Source Default Distance Connected interface 0 Static Route 1 EIGRP Summary Route 5 External BGP 20 Internal EIGRP 90 IGRP 100 OSPF 110 IS-IS 115 RIP 120 EGP 140 Internal BGP 200 Unknown 255

IOS ignores these routes


Distance Vector vs Link StateDistance Vector vs Link State• Distance Vector

– Each router knows: • Direction (vector)• Distance (hops)

– Example. Destination is:• out S0• 3 hops away

– Does not know exact map to destination.

3 hops



– To reach Joe’s office:Go out middle door & pass through 3 buildings.At each building, you’ll be told which door to exit

– Which office could be Joe’s?

3





3 2





3 2

1





3 2

1 0





3 2

1 0 Joe


Distance Vector vs Link StateDistance Vector vs Link State• Link State

– Each router knows:• Overall map of network• Shortest path to destination



– To reach Joe’s office:Follow Campus Map.Take shortest path.

Joe


Distance Vector vs Link StateDistance Vector vs Link State• Distance Vector Updates (RIP example)

– Each router gossips to its direct neighbor.– Gossip is sent every 30 seconds.– Takes time to pass the gossip to the end of the line.– When all routers have received the gossip they are “converged”. Until then,

the routers posses conflicting knowledge.

A tells B

A B C D E F

B tells C C tells D D tells E E tells F



– Each router sends information about its links to all other routers.– Changes in network topology trigger these link state

advertisements.– Each router then develops a full map of the network.

A tells all other routers when it learns of a change in the network

A B C D E F

When any other router detects a change, it also tells everyone.

Down


RIPRIP• Distance-Vector• Updates: every 30 seconds • Metric: Hops • Default administrative distance: 120• Convergence: slow• Versions 1 & 2


IGRPIGRP• Distance-Vector• Updates: every 90 seconds • Metric: bandwidth & delay (defaults)

Can also include load, reliability • Default administrative distance: 100• Convergence: faster than RIP


Configuring Dynamic RoutingConfiguring Dynamic Routing1.Specify the routing protocol.

– Ordinarily, all routers must run the same protocol.

2.Specify all directly connected networks on which the router will send and receive route updates (also called advertisements).– Network are specified by major network numbers, not

subnets. Example - here the network is 10.0.0.0:

10.2.0.2/16 10.3.0.1/16


CommandsCommands• Configuring RIP

oak(config)#router ripoak(config-router)#network 10.0.0.0oak(config-router)#network 192.168.3.0oak(config-router)#^Z

Enables RIP routing

Sets RIP to send/receive updates on these directly connected networks


CommandsCommands• Configuring RIP version 2 - same as RIP but

– adds version 2 statement

– version should be the same for all routers

oak(config)#router ripoak(config-router)#version 2oak(config-router)#network 10.0.0.0oak(config-router)#network 192.168.4.0oak(config-router)#^Z

Enables RIP routing Sets RIP version 2


CommandsCommands• Configuring IGRP - same as RIP, but

– includes an autonomous system number

– AS must be same for all routers

oak(config)#router igrp 40oak(config-router)#network 10.0.0.0oak(config-router)#network 192.168.3.0oak(config-router)#^Z

Enables IGRP routing Autonomous System #


CommandsCommands• Configuring a static route - outgoing interface

fre(config)#ip route 192.168.1.0 255.255.255.0 s0fre(config)#^Z

Destination network & mask

Route to network via this outgoing interface


CommandsCommands• Configuring a static route - next hop

fre(config)#ip route 192.168.1.0 255.255.255.0 s0fre(config)#ip route 192.168.1.0 255.255.255.0 10.1.0.2fre(config)#^Z

Destination network & mask

Route to network via this next hop address.

Use this format to improve clarity of routing tables.


ComandsComands• Specifying next hop

– It is the ip address of nearest interface of the neighbor router along the route.

– From Router B, this is the next hop to LAN A:

LAN

D

LAN

C

LAN

A

B


ComandsComands• From Router B, what is the next hop to

– the 192.168.3.0 net?– 10.2.0.2

19

2.1

68

.1.0

Ne

t

B 19

2.1

68

.3.0

Ne

t

19

2.1

68

.4.0

Ne

t

10

.1.0

.1

10

.1.0

.2

10

.2.0

.1

10

.2.0

.2

10

.3.0

.1

10

.3.0

.2


ComandsComands• From Router B, what is the next hop to

– the 192.168.4.0 net?– 10.2.0.2

19

2.1

68

.1.0

Ne

t

B 19

2.1

68

.3.0

Ne

t

19

2.1

68

.4.0

Ne

t

10

.1.0

.1

10

.1.0

.2

10

.2.0

.1

10

.2.0

.2

10

.3.0

.1

10

.3.0

.2

– The next hop is always on the neighbor router!


ComandsComands• From Router B, what are the only two possible next hop addreses?

– 10.1.0.1

19

2.1

68

.1.0

Ne

t

B 19

2.1

68

.3.0

Ne

t

19

2.1

68

.4.0

Ne

t

10

.1.0

.1

10

.1.0

.2

10

.2.0

.1

10

.2.0

.2

10

.3.0

.1

10

.3.0

.2

– 10.2.0.2

10

.1.0

.1

10

.2.0

.2


CommandsCommands• Static route - administrative distance parameter• Optional

oak(config)#ip route 10.1.0.0 255.255.0.0 s0 121oak(config)#^Z

Administrative Distance


CommandsCommands• Static route - administrative distance• If unspecified, default distance is 0

for outgoing interface format.• These routes will show as S but will be listed as directly connected in the routing table.

oak(config)#ip route 10.1.0.0 255.255.0.0 s0


CommandsCommands• Static route - administrative distance• If unspecified, default distance is 1

for next hop format.• These routes will show as S (static) in the routing table.

oak(config)#ip route 10.1.0.0 255.255.0.0 10.3.0.1


CommandsCommands• Configuring a default route (default network)

method 1 - set a default route to the wildcard network & subnet of 0.0.0.0 0.0.0.0

hay(config)#ip route 0.0.0.0 0.0.0.0 192.168.0.1hay(config)#^Z

Wildcard network & mask

Route to default network via this “next hop” address -

the address of the direct neighbor interface.See http://www.cisco.com/warp/public/105/default.html



10.0.0.0/16 is subnetted, 2 subnetsC 10.2.0.0 is directly connected, Serial1R 10.1.0.0 [120/1] via 10.2.0.1, 00:00:18, Serial1R 192.168.1.0/24 [120/2] via 10.2.0.1, 00:00:18, Serial1S 192.168.2.0/24 [1/0] via 10.2.0.1C 192.168.3.0/24 is directly connected, Ethernet0R* 0.0.0.0/0 [1/0] via 10.2.0.1

CommandsCommands• method 1 - RIP will automatically redistribute the default route to

the wildcard network & subnet of 0.0.0.0 0.0.0.0 to other routers:

Dis

trib

uted

fro

m h

ayw

ard

to o

akla

nd b

y R

IP


CommandsCommands• Configuring a default route (default network)

method 2: (presented in the curriculum)

ip default-network xxx.xxx.xxx.xxx

hay(config)#ip default-network 192.168.0.0 hay(config)#^Z

Send default traffic here

See http://www.cisco.com/warp/public/105/default.html


CommandsCommands• Default network must be

– defined on each routeror

– redistributed by RIP to other routers


CommandsCommands• Redistribution methods:

– 0.0.0.0: • With IOS Version 12.0, RIP automatically distributes a route to 0.0.0.0 to other routers.• With IOS Version 12.1 or later, you must add the

default-information originate command:

hay(config)#router riphay(config-router)#default-information originate

hay(config)#router riphay(config-router)#redistribute static

– ip default-network: To force RIP to redistribute the default route, you must add the redistribute static command:


CommandsCommands• show ip route• displays routing table


R 192.168.4.0/24 [120/1] via 10.3.0.2, 00:00:11, Serial0 10.0.0.0/16 is subnetted, 3 subnetsC 10.2.0.0 is directly connected, Serial1C 10.3.0.0 is directly connected, Serial0R 10.1.0.0 [120/1] via 10.2.0.1, 00:00:18, Serial1R* 192.168.1.0/24 [120/2] via 10.2.0.1, 00:00:18, Serial1S 192.168.2.0/24 [1/0] via 10.2.0.1C 192.168.3.0/24 is directly connected, Ethernet0

RouteSource

[Administrative Distance/Metric]


CommandsCommands• show ip protocols

oak(config)#show ip protocols

Routing Protocol is "rip" Sending updates every 30 seconds, next due in 2 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Redistributing: rip Routing for Networks: 10.0.0.0 192.168.4.0

Update Distance: (default is 120)


CommandsCommands• show ip interfaces• interface detail

oak(config)#show ip interfaces

Ethernet0 is up, line protocol is up Internet address is 192.195.78.24, subnetmask 255.255.255.240 Broadcast address is 255.255.255.255 Address determined by non-volatile memory MTU is 1500 bytes Helper address is not set Secondary address 131.192.115.2, subnet mask 255.255.255.0 Directed broadcast forwarding is enabled Outgoing access list is not set Inbound access list is not set Proxy ARP is enabled Split horizon is enabled


CommandsCommands• debug ip rip• Displays rip updates as they are received & sent by router• Temporary troubleshooting only -

must not be left on!• Turn off with• no debug ip rip or no debug all

cisco networking academy chabot college elec 99.08 ip routing protocol highlights

Documents

serial1 c

serial1 r

serial0 c

serial0 r

subnetted c

subnets c

ip route r

serial1 s