1 Routing Protocols and Configuration Instructor: Te-Lung Liu Program Associate Researcher NCHC, South Region Office

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Routing Protocols and Configuration

Instructor: Te-Lung Liu

Program Associate Researcher

NCHC, South Region Office

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Outline

Static Route

Default Route

Dynamic Route

Routing Metrics

Routing ProtocolsDistance Vector

Link State

Configure Dynamic Routing Protocols

Verifying Commands

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Static Route

Static route knowledge is administered manually by a network administrator who enters it into a router's configuration.

The administrator must manually update this static route entry whenever an internetwork topology change requires an update

"stub" network

Single connection only that no routing update is required

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Static Route

199.13.1.1

199.13.1.2199.13.2.0 /255.255.255.0

199.13.2.1

Router(config)# ip route 199.13.2.0 255.255.255.0 199.13.1.2

specified for "stub" network connectionRouter(config)# ip route network [mask] address [adm_distance]

Administrative distance (0~255) is a rating of the trustworthiness of a routing information source. The higher the number, the lower the trustworthiness rating

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Default Route

If the next hop is not explicitly listed in the routing table, send it to default routerRouter(config)# ip default-network network-number

Network number must exist in routing table

Company or Campus

Internet

10.0.0.0192.168.1.0

Router(config)# ip default-network 192.168.1.0

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Dynamic Route

The route knowledge is automatically updated by a routing process whenever new information is received from the internetwork.

Changes in dynamic knowledge are exchanged between routers as part of the update process.

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Routing Metrics

bandwidth -- the data capacity of a link; (normally, a 10 Mbps Ethernet link is preferable to a 64 kbps leased line)

delay -- the length of time required to move a packet along each link from source to destination

load -- the amount of activity on a network resource such as a router or link

reliability -- usually refers to the error rate of each network link

hop count -- the number of routers a packet must travel through before reaching its destination

ticks -- the delay on a data link using IBM PC clock ticks (approximately 55 milliseconds).

cost -- an arbitrary value, usually based on bandwidth, monetary expense, or other measurement, that is assigned by a network administrator

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Routing Protocols

Distance VectorRouting table is exchanged with the neighbor routers

Ex. RIP,IGRP

Link StateLink state is multicast to all routers in the same AS

Full view of network topology

Faster convergence

Ex. OSPF

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Distance Vector

Each router periodically send its routing table to its neighbors.

When the topology in a distance-vector protocol network changes, routing table updates must occur.

Count to Infinity and Routing Loop ProblemSplit Horizon and Hold-down Timers

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Net Next Cost 1 direct 0 2 direct 0 3 B 1 4 B 1

Net Next Cost 1 A 1 2 direct 0 3 direct 0 4 direct 0 5 C 1

Net Next Cost 2 B 1 3 B 1 4 direct 0 5 direct 0

Router A Router B Router C1 23

4 5

Net Next Cost 1 direct 0 2 direct 0

Net Next Cost 2 direct 0 3 direct 0 4 direct 0


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Net Next Cost 1 direct 0 2 direct 0 3 B 1 4 B 1


Net Next Cost 2 B 1 3 B 1 4 direct 0 5 direct 0

Net Next Cost 1 direct 0 2 direct 0 3 B 1 4 B 1 5 B 2


Net Next Cost 1 B 2 2 B 1 3 B 1 4 direct 0 5 direct 0

Router A Router B Router C1 23

4 5

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Problem : Count to Infinity

Router A Router B1 2 3

Net Next Cost 1 direct 0 2 direct 0 3 B 1

Net Next Cost 1 A 1 2 direct 0 3 direct 0

removed


Net Next Cost 1 A 1 2 direct 0 3 A 2

13







::

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Solution : Split HorizonNot update the neighbor entries that comes from itself




removed


Net Next Cost 1 A 1 2 direct 0

A skipsthis entry

when telling B

Or carries “next hop” in

messages such that B can ignore

(e.g. RIP)

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Solution : Poison ReverseClaim infinity cost to the neighbor when direct links become invalid




∞

Net Next Cost 1 direct 0 2 direct 0 3 B ∞

A updatesthis entry by

infinity

Net Next Cost 1 A 1 2 direct 0 3 direct ∞

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Problem : Routing Loops

Packets never reach their destination but instead cycle repeatedly through the same group of network nodes

Router B

Router C

Router D Router E

Network 1

Net Next Cost 1 B 3

Router A

With split horizon, B will not be updated by AHowever, C will. Then it passes to D, B, A, C ......=> Count to infinity still occurs!

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Solution : Hold-down Timer

When a router receives an update from a neighbor indicating that a previously accessible network is now inaccessible, the router marks the route as inaccessible and starts a hold-down timer.

If at any time before the hold-down timer expires an update is received from the same neighbor indicating that the network is again accessible, the router marks the network as accessible and removes the hold-down timer.

If an update arrives from a different neighboring router with a better metric than originally recorded for the network, the router marks the network as accessible and removes the hold-down timer

If at any time before the hold-down timer expires an update is received from a different neighboring router with a poorer metric, the update is ignored.

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RIP timer

Update timer 30 secs

Invalid timer 90 secs

Holddown timer 180 secs

Flush timer 270 secs

FlushInvalidUpdate Holddownexpire

Holddown

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Link State

Link-state routing algorithm maintains full knowledge of distant routers and how they interconnect.

Each router sends its link-state advertisements (LSAs) to all routers in the same AS/Area

Routers can maintain the network topology with all LSAs and then use shortest-path algorithm to determine the route.

Whenever a link-state topology changes, the routers that first become aware of the change send information to other routers or to a designated router that all other routers can use for updates.

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A

B

C

A

C

D

B

C

DA

B

C

DA

B

D

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Link State

ConcernsProcessing and memory requirements

Bandwidth requirements

Problem :Unsynchronized LSAs leading to inconsistent path decisions amongst routers

A

B

C

D

Network is down and up again soon

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Dynamic routing protocol setting - enter router configuration mode

Enter router config mode

Router(config)# router protocol [keyword]

specify the networks to be routedRouter(config-router)# network network-number

RIPLab1(config)# router rip

Lab1(config-router)# network 200.177.1.0


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IGRPAS number is used as keyword

Lab1(config)# router igrp 100



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IGRP v.s RIPBoth are Distance Vector algorithms

RIP : hop count only

IGRP :bandwidth, delay, load, reliability

Maximum hopRIP : 15

IGRP : 255

Updating TimerRIP : 30sec

IGRP : 90 sec

Administrative DistanceRIP : 120

IGRP : 100

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Verifying Commands

lab-a#show ip protocols

Routing Protocol is "rip"

Sending updates every 30 seconds, next due in 0 seconds

Invalid after 180 seconds, hold down 180, flushed after 240

Outgoing update filter list for all interfaces is

Incoming update filter list for all interfaces is

Redistributing: rip

Default version control: send version 1, receive any version

Interface Send Recv Triggered RIP Key-chain

FastEthernet0/0 1 1 2

Serial0/0 1 1 2

Automatic network summarization is in effect

Routing for Networks:

192.168.1.0

192.168.10.0

Routing Information Sources:

Gateway Distance Last Update

192.168.10.2 120 00:00:15

Distance: (default is 120)

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Verifying Commands

lab-a#show ip route

Codes: 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

R 192.168.30.0/24 [120/2] via 192.168.10.2, 00:00:21, Serial0/0

C 192.168.10.0/24 is directly connected, Serial0/0

R 192.168.4.0/24 [120/3] via 192.168.10.2, 00:00:21, Serial0/0

R 192.168.20.0/24 [120/1] via 192.168.10.2, 00:00:21, Serial0/0

C 192.168.1.0/24 is directly connected, FastEthernet0/0

R 192.168.2.0/24 [120/1] via 192.168.10.2, 00:00:21, Serial0/0

R 192.168.3.0/24 [120/2] via 192.168.10.2, 00:00:21, Serial0/0

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Verifying Commands

lab-a#debug ip rip

02:54:05: RIP: build update entries

02:54:05: network 192.168.2.0 metric 2

02:54:05: network 192.168.3.0 metric 3

02:54:05: network 192.168.4.0 metric 4

02:54:05: network 192.168.10.0 metric 1

02:54:05: network 192.168.20.0 metric 2

02:54:05: network 192.168.30.0 metric 3

02:54:05: RIP: sending v1 update to 255.255.255.255 via Serial0/0 (192.168.10.1)

02:54:05: RIP: build update entries

02:54:05: network 192.168.1.0 metric 1

02:54:07: RIP: received v1 update from 192.168.10.2 on Serial0/0

02:54:07: 192.168.2.0 in 1 hops

02:54:07: 192.168.3.0 in 2 hops

02:54:07: 192.168.4.0 in 3 hops

02:54:07: 192.168.20.0 in 1 hops

02:54:07: 192.168.30.0 in 2 hops

Documents

1 Routing Protocols and Configuration Instructor: Te-Lung Liu Program Associate Researcher NCHC, South Region Office