Wednesday, July 29, 2009
For CCNA communicating success, you had meliorate undergo what separate scope is, how to invoke it off, and when to invoke it off. Knowing when to invoke separate scope soured is also essential in creation networks, because it crapper drive a hub-and-spoke meshwork to hit half routing tables on the spokes.
Split scope exists for a rattling beatific think - routing wrap prevention. The conception of separate scope states that a router cannot beam an advertizing for a line discover the aforementioned programme that it came in on. Split scope is on by choice on every interfaces streaming RIP, IGRP, and EIGRP.
In this CCNA tutorial, R1 module serve, as the hub and R2 and R3 module be the spokes. We'll prototypal configure EIGRP over the 172.16.123.0 /24 network, the meshwork conjunctive the threesome routers.
R1#conf t
R1(config)#router eigrp 100
R1(config-router)#no auto-summary
R1(config-router)#network 172.12.123.0 0.0.0.255
R2#conf t
R2(config)#router eigrp 100
R2(config-router)#no auto-summary
R2(config-router)#network 172.12.123.0 0.0.0.255
R3#conf t
R3(config)#router eigrp 100
R3(config-router)#no auto-summary
R3(config-router)#network 172.12.123.0 0.0.0.255
Running exhibit ip eigrp edge on R1 shows that adjacencies to R2 and R3 are up.
R1#show ip eigrp neighbor
IP-EIGRP neighbors for impact 100
H Address Interface Hold Uptime SRTT RTO Q Seq Type
(sec) (ms) Cnt Num
1 172.12.123.3 Se0/0 11 00:02:45 1 5000 0 1
0 172.12.123.2 Se0/0 161 00:03:01 1 5000 0 1
Each router module today promote its loopback come via EIGRP.
R1#conf t
R1(config)#router eigrp 100
R1(config-router)#network 1.1.1.0 0.0.0.255
R2#conf t
R2(config)#router eigrp 100
R2(config-router)#network 2.2.2.0 0.0.0.255
R3#conf t
R3(config)#router eigrp 100
R3(config-router)#network 3.3.3.0 0.0.0.255
Running exhibit ip eigrp line on apiece router shows that R1 has a line for both R2s and R3s loopback. R2 and R3 module exclusive wager R1s loopback address, and not apiece others. Why?
R1#show ip line eigrp
2.0.0.0/24 is subnetted, 1 subnets
D 2.2.2.0 [90/2297856 via 172.12.123.2, 00:03:19, Serial0/0
3.0.0.0/24 is subnetted, 1 subnets
D 3.3.3.0 [90/2297856 via 172.12.123.3, 00:03:04, Serial0/0
R2#show ip line eigrp
1.0.0.0/24 is subnetted, 1 subnets
D 1.1.1.0 [90/2297856 via 172.12.123.1, 00:03:40, Serial0/0.123
R3#show ip line eigrp
1.0.0.0/24 is subnetted, 1 subnets
D 1.1.1.0 [90/2297856 via 172.12.123.1, 00:05:17, Serial0/0.31
EIGRP uses Split Horizon by choice to preclude routing loops. In this lab, though, it prevents flooded meshwork reachability. R2 and R3 both modify edge relationships with R1s Serial fleshly interface. R2 advertises its loopback come to R1s Serial interface, as does R3. Split Horizon does not earmark a line to be advertised backwards discover the aforementioned programme it was conventional on. This prevents R1 from business R2s loopback to R3, or R3s loopback to R2.
Split Horizon staleness be unfit to earmark flooded meshwork reachability in this lab. To do so, separate no ip split-horizon eigrp 100 on R1s Serial interface. When Split Horizon is disabled, that module drive the neighbor
relationships to fail, and then reestablish. Run exhibit ip line eigrp 100 on both R2 and R3. The pertinent line to the far loopback come module today appear.
R1#conf t
R1(config)#int serial0
R1(config-if)#no ip split-horizon eigrp 100
10:02:23: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor 172.12.123.2 (Serial0/0) down: separate scope changed
10:02:23: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor 172.12.123.3 (Serial0/0) down: separate scope changed
10:02:27: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor 172.12.123.3 (Serial0/0) ip: newborn adjacency
10:02:54: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor 172.12.123.2 (Serial0/0) ip: newborn adjacency
R2#show ip line eigrp
1.0.0.0/24 is subnetted, 1 subnets
D 1.1.1.0 [90/2297856 via 172.12.123.1, 00:00:06, Serial0/0.123
3.0.0.0/24 is subnetted, 1 subnets
D 3.3.3.0 [90/2809856 via 172.12.123.1, 00:00:06, Serial0/0.123
R3#show ip line eigrp
1.0.0.0/24 is subnetted, 1 subnets
D 1.1.1.0 [90/2297856 via 172.12.123.1, 00:00:12, Serial0/0.31
2.0.0.0/24 is subnetted, 1 subnets
D 2.2.2.0 [90/2809856 via 172.12.123.1, 00:00:12, Serial0/0.31
Disabling separate scope should be finished with care, but lettered when and where to do so shows that you genuinely see how this profession entireness - and that's a bounteous travel on the artefact to earning your CCNA!
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