1
Routing Protocols and Configuration
Instructor: Te-Lung Liu
Program Associate Researcher
NCHC, South Region Office
2
Outline
Static Route
Default Route
Dynamic Route
Routing Metrics
Routing ProtocolsDistance Vector
Link State
Configure Dynamic Routing Protocols
Verifying Commands
3
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
4
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
5
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
6
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.
7
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
8
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
9
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
10
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
Net Next Cost 4 direct 0 5 direct 0
11
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
Net Next Cost 1 direct 0 2 direct 0 3 B 1 4 B 1 5 B 2
Net Next Cost 1 A 1 2 direct 0 3 direct 0 4 direct 0 5 C 1
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
12
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 direct 0 2 direct 0 3 B 1
Net Next Cost 1 A 1 2 direct 0 3 A 2
13
Net Next Cost 1 direct 0 2 direct 0 3 B 1
Net Next Cost 1 A 1 2 direct 0 3 A 2
Net Next Cost 1 direct 0 2 direct 0 3 B 3
Net Next Cost 1 A 1 2 direct 0 3 A 2
Net Next Cost 1 direct 0 2 direct 0 3 B 3
Net Next Cost 1 A 1 2 direct 0 3 A 4
::
14
Solution : Split HorizonNot update the neighbor entries that comes from itself
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 direct 0 2 direct 0
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)
15
Solution : Poison ReverseClaim infinity cost to the neighbor when direct links become invalid
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
∞
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 ∞
16
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!
17
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.
18
RIP timer
Update timer 30 secs
Invalid timer 90 secs
Holddown timer 180 secs
Flush timer 270 secs
FlushInvalidUpdate Holddownexpire
Holddown
19
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.
20
A
B
C
A
C
D
B
C
DA
B
C
DA
B
D
21
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
22
Configure Dynamic Routing Protocols
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
Lab1(config-router)# network 210.3.1.0
23
Configure Dynamic Routing Protocols
IGRPAS number is used as keyword
Lab1(config)# router igrp 100
Lab1(config-router)# network 200.177.1.0
Lab1(config-router)# network 210.3.1.0
24
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
25
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)
26
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
27
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