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EIGRP

i've tested network-2 routers:

2610#sh ip int brief

Interface IP-Address OK? Method Status Protocol

Ethernet0/0 A.B.C.1 YES NVRAM up up

Serial0/0 unassigned YES TFTP up up

Serial0/0.1 C.D.E.22 YES NVRAM up up

Serial0/0.2 192.168.100.1 YES NVRAM up up

Serial0/0.3 unassigned YES unset up up

Loopback0 192.168.17.1 YES manual up up

Loopback1 131.108.1.1 YES manual up up

Loopback2 131.108.2.1 YES manual up up

Loopback3 131.108.3.1 YES manual up up

Loopback4 131.108.4.1 YES manual up up

Loopback5 131.108.5.1 YES manual up up

Loopback6 131.108.6.1 YES manual up up

Loopback7 192.168.13.1 YES manual up up

Loopback8 131.108.7.1 YES manual up up

Loopback9 131.108.8.1 YES manual up up

Loopback10 131.108.9.1 YES manual up up

Loopback11 131.108.10.1 YES manual up up

Loopback12 131.108.11.1 YES manual up up

Loopback13 131.108.12.1 YES manual up up

---------------------

!

router eigrp 1

network 131.108.0.0

network A.B.C.0

no auto-summary

!

================================

c1603#sh ip int brief

Interface IP-Address OK? Method Status Protocol

Ethernet0 A.B.C.111 YES NVRAM up up

Loopback0 192.168.20.1 YES manual up up

Loopback1 131.108.16.1 YES manual up up

Loopback2 131.108.17.1 YES manual up up

Loopback3 192.168.16.1 YES manual up up

Loopback4 131.108.18.1 YES manual up up

Loopback5 131.108.19.1 YES manual up up

Loopback6 131.108.20.1 YES manual up up

Loopback7 131.108.21.1 YES manual up up

Loopback8 131.108.22.1 YES manual up up

Loopback9 131.108.23.1 YES manual up up

Loopback10 131.108.24.1 YES manual up up

Loopback11 131.108.25.1 YES manual up up

Loopback12 131.108.26.1 YES manual up up

Loopback13 131.108.27.1 YES manual up up

------------------------

!

router eigrp 1

network 131.108.0.0

network A.B.C.0

no auto-summary

!

==============================

2610#sh ip route eigrp

131.108.0.0/16 is variably subnetted, 14 subnets, 2 masks

D 131.108.0.0/20 is a summary, 00:13:44, Null0

D 131.108.16.0/20 [90/409600] via A.B.C.111, 00:13:41, Ethernet0/0

c1603#sh ip route eigrp

131.108.0.0/16 is variably subnetted, 14 subnets, 2 masks

D 131.108.0.0/20 [90/409600] via A.B.C.1, 00:14:21, Ethernet0

D 131.108.16.0/20 is a summary, 00:18:25, Null0

Is't right that i route

D 131.108.16.0/20 is a summary, 00:18:25, Null0

in both route tables. Why i have Null0?

1 ACCEPTED SOLUTION

Accepted Solutions
Bronze

Re: EIGRP

It looks like the 2610 is summarizing its connected networks as 131.108.0.0/20 towards the 1603. This means that instead of advertising all of its connected routes to the 1603, it sends one route summarizing these connected networks. Likewise, the 1603 is advertising 131.108.16.0/20 to the 2610, instead of all of its connected networks individually. When a router sends a summary route, its own routing table shows the summary route as being connected to interface Null 0, or the bit bucket. This means that it will dump traffic for any destination in the summary range that does not have a longer match than the summary.

This is accomplished with the "ip summary-address eigrp" interface command. If you check your running config, you will see these commands in the routers' ethernet interfaces.

HTH

Mark

1 REPLY
Bronze

Re: EIGRP

It looks like the 2610 is summarizing its connected networks as 131.108.0.0/20 towards the 1603. This means that instead of advertising all of its connected routes to the 1603, it sends one route summarizing these connected networks. Likewise, the 1603 is advertising 131.108.16.0/20 to the 2610, instead of all of its connected networks individually. When a router sends a summary route, its own routing table shows the summary route as being connected to interface Null 0, or the bit bucket. This means that it will dump traffic for any destination in the summary range that does not have a longer match than the summary.

This is accomplished with the "ip summary-address eigrp" interface command. If you check your running config, you will see these commands in the routers' ethernet interfaces.

HTH

Mark

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