EIGRP Manual Summarization

[quanghung91]

Hi everybody,

I have a problem with EIGRP manual summarization. As you know, you can configure a summary command on an interface, but if you want to send a summary route and a specific route that you have use Leak-map. I tried a lab on GNS3, and I realized that I can add two 'ip summary eigrp 10 x.x.x.x' for the summary route and the specific route. Can someone tell the answer?

[daniel.dib · Accepted solution]

I did a lab. This is before filtering:

R2#sh ip route eigrp

     10.0.0.0/24 is subnetted, 1 subnets

D       10.0.0.0 [90/409600] via 12.12.12.1, 00:00:02, FastEthernet0/0

Now to announce only the summary on R1:

Enter configuration commands, one per line.  End with CNTL/Z.

R1(config)#int f0/0

R1(config-if)#ip summary-address eigrp 1 10.0.0.0 255.0.0.0

R2#sh ip route eigrp

D    10.0.0.0/8 [90/409600] via 12.12.12.1, 00:00:18, FastEthernet0/0

Only the summary is received. Let's see if we can announce the more specific one as well:

R1(config-if)#ip summary-address eigrp 1 10.0.0.0 255.255.255.0

R1(config-if)#do sh run int f0/0

Building configuration...

Current configuration : 197 bytes

!

interface FastEthernet0/0

ip address 12.12.12.1 255.255.255.0

ip summary-address eigrp 1 10.0.0.0 255.255.255.0 5

ip summary-address eigrp 1 10.0.0.0 255.0.0.0 5

R2#sh ip route eigrp

     10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

D       10.0.0.0/24 [90/409600] via 12.12.12.1, 00:00:25, FastEthernet0/0

D       10.0.0.0/8 [90/409600] via 12.12.12.1, 00:01:17, FastEthernet0/0

That seems to work. How about adding another one?

R1(config-if)#ip summary-address eigrp 1 10.0.0.0 255.255.0.0

R1(config-if)#do sh run int f0/0

*Mar  1 00:03:52.207: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 12.12.12.2 (FastEthernet0/0) is resync: summary configured

R1(config-if)#do sh run int f0/0

Building configuration...

Current configuration : 248 bytes

!

interface FastEthernet0/0

ip address 12.12.12.1 255.255.255.0

ip summary-address eigrp 1 10.0.0.0 255.255.255.0 5

ip summary-address eigrp 1 10.0.0.0 255.255.0.0 5

ip summary-address eigrp 1 10.0.0.0 255.0.0.0 5

R2#sh ip route eigrp

     10.0.0.0/8 is variably subnetted, 3 subnets, 3 masks

D       10.0.0.0/24 [90/409600] via 12.12.12.1, 00:01:12, FastEthernet0/0

D       10.0.0.0/16 [90/409600] via 12.12.12.1, 00:00:16, FastEthernet0/0

D       10.0.0.0/8 [90/409600] via 12.12.12.1, 00:02:04, FastEthernet0/0

So it seems we can add any number of routes we wish as long as there is a component in the summary.

However the usual approach would be to leak the prefix.

Daniel Dib
CCIE #37149

[quanghung91]

Thanks Daniel for your response,

What advantages is it when using Virtual template interface and Leak-map compared to using many 'ip summary eigrp...' commands? because the second one is simpler.

[daniel.dib]

It depends on the number of routes I suppose. If you want to leak many routes you could have to type in many commands under the interface. For just a few it should not matter much. I'm not sure of what your scenario is. Are you using PPP?

Daniel Dib
CCIE #37149