Auto Summarization

[gowdakssujan]

On both Routers R1 & R2.

1)Eigrp enabled. 

2)Automatic network summarization is in effect.

R1#sh ip route eigrp

10.0.0.0/24 is subnetted, 4 subnets

D 10.10.13.0 [90/30720] via 10.10.12.2, 00:10:36, FastEthernet0/0

R2#sh ip route eigrp

10.0.0.0/24 is subnetted, 4 subnets

D 10.10.10.0 [90/30720] via 10.10.12.1, 00:11:23, FastEthernet0/0

D 10.10.11.0 [90/284160] via 10.10.12.1, 00:11:23, FastEthernet0/0

Why there is no summarization??????

[Giuseppe Larosa]

Hello,

EIGRP performs automatic summarization at major network boundary.

In your case all links use subnets taken from 10.0.0.0/8 Class A major network.

To see auto summarization in action change the network between R1 and R2 to 192.168.1.0/24.

R1 will send 10.0.0.0/8 to R2 and R2 will do the same as a result of change of major network out of respective Fas0/0.

Hope to help

Giuseppe

[gowdakssujan]

Is it same with RIPv2?

[balaji.bandi]

yes it is the same case with RiPv2 also.

[gowdakssujan]

But here 172.16.1.0/24 is not a major network. Still, it is summarizing, Why????

R1#sh ip route eigrp

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

D 10.0.0.0/8 is a summary, 00:03:05, Null0

172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks

D 172.16.0.0/16 is a summary, 00:03:05, Null0

R1#sh ip route eigrp

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

D 10.0.0.0/8 is a summary, 00:03:05, Null0

172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks

D 172.16.0.0/16 is a summary, 00:03:05, Null0

[balaji.bandi]

Depends io version you using in the lab, by default old routers autosummarisation turned on.

you can check show ip protocol 

if you like to turn off auto summary

config t

router eigrp XXX

no auto summary

and post the show ip route eigrp and show ip protocol information

[gowdakssujan]

Am using 2811 router; auto summarization is enabled by default.

R1>sh ip pro

Routing Protocol is "eigrp 10 "

Outgoing update filter list for all interfaces is not set

Incoming update filter list for all interfaces is not set

Default networks flagged in outgoing updates

Default networks accepted from incoming updates

EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0

EIGRP maximum hopcount 100

EIGRP maximum metric variance 1

Redistributing: eigrp 10

Automatic network summarization is in effect

Automatic address summarization:

10.0.0.0/8 for FastEthernet0/0

Summarizing with metric 28160

172.16.0.0/16 for FastEthernet0/1

Summarizing with metric 28160

Maximum path: 4

Routing for Networks:

0.0.0.0

Routing Information Sources:

Gateway Distance Last Update

172.16.1.2 90 4793887

R1>sh ip pro

Routing Protocol is "eigrp 10 "

Outgoing update filter list for all interfaces is not set

Incoming update filter list for all interfaces is not set

Default networks flagged in outgoing updates

Default networks accepted from incoming updates

EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0

EIGRP maximum hopcount 100

EIGRP maximum metric variance 1

Redistributing: eigrp 10

Automatic network summarization is in effect

Automatic address summarization:

10.0.0.0/8 for FastEthernet0/0

Summarizing with metric 28160

172.16.0.0/16 for FastEthernet0/1

Summarizing with metric 28160

Maximum path: 4

Routing for Networks:

0.0.0.0

Routing Information Sources:

Gateway Distance Last Update

172.16.1.2 90 4793887

[gowdakssujan]

1>sh ip rou ei

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

D 10.0.0.0/8 is a summary, 02:25:05, Null0

172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks

D 172.16.0.0/16 is a summary, 02:25:05, Null0

[balaji.bandi]

see here "Automatic network summarization is in effect"

turn off " no auto-summary" and try.

[Giuseppe Larosa]

Hello gowdakssujan,

this is correct behavior for auto summarization to be triggered it is enough to have an outgoing interface that belongs to a different Major network and 172.16.1.0/24 is part of net 172.16.0./16 even a subnet of a different Major network is seen as a MAjor network transition.

EIGRP is classless and carries subnet masks so having a different Major network or having a subnet of a different Major network is treated in the same way for auto-summarization.

Hope to help

Giuseppe