EIGRP auto-summary

Ok, I was working on this INE topology on EIGRP & auto-summary

When I enable EIGRP without summary, the output on R2 is this:

150.1.0.0/32 is subnetted, 10 subnets

D 150.1.1.1 [90/27059200] via 155.1.0.5, 00:00:12, Tunnel0
D 150.1.3.3 [90/27084800] via 155.1.0.5, 00:00:12, Tunnel0
D 150.1.4.4 [90/27033600] via 155.1.0.5, 00:00:13, Tunnel0
D 150.1.5.5 [90/27008000] via 155.1.0.5, 00:00:12, Tunnel0
D 150.1.6.6 [90/27059200] via 155.1.0.5, 00:00:12, Tunnel0
D 150.1.7.7 [90/27084800] via 155.1.0.5, 00:00:12, Tunnel0
D 150.1.8.8 [90/27033600] via 155.1.0.5, 00:00:13, Tunnel0
D 150.1.9.9 [90/27110400] via 155.1.0.5, 00:00:12, Tunnel0
D 150.1.10.10 [90/27059200] via 155.1.0.5, 00:00:13, Tunnel0
155.1.0.0/16 is variably subnetted, 15 subnets, 2 masks
D 155.1.5.0/24 [90/26905600] via 155.1.0.5, 1d22h, Tunnel0
D 155.1.7.0/24 [90/26982400] via 155.1.0.5, 1d22h, Tunnel0
D 155.1.8.0/24 [90/26931200] via 155.1.0.5, 1d22h, Tunnel0
D 155.1.9.0/24 [90/27008000] via 155.1.0.5, 1d22h, Tunnel0
D 155.1.10.0/24 [90/26956800] via 155.1.0.5, 1d22h, Tunnel0
D 155.1.13.0/24 [90/26956800] via 155.1.0.5, 1d22h, Tunnel0
D 155.1.37.0/24 [90/26982400] via 155.1.0.5, 1d22h, Tunnel0
D 155.1.45.0/24 [90/26905600] via 155.1.0.5, 1d22h, Tunnel0
D 155.1.58.0/24 [90/26905600] via 155.1.0.5, 1d22h, Tunnel0
D 155.1.67.0/24 [90/26956800] via 155.1.0.5, 1d22h, Tunnel0
D 155.1.79.0/24 [90/26982400] via 155.1.0.5, 1d22h, Tunnel0
D 155.1.108.0/24 [90/26931200] via 155.1.0.5, 1d22h, Tunnel0
D 155.1.146.0/24 [90/26931200] via 155.1.0.5, 1d22h, Tunnel0

All the routers in the network have EIGRP turned on without summary. After auto-summary is turned on, the output looks like this:

150.1.0.0/16 is variably subnetted, 2 subnets, 2 masks

D 150.1.0.0/16 is a summary, 00:00:08, Null0
155.1.0.0/16 is variably subnetted, 16 subnets, 3 masks
D 155.1.0.0/16 is a summary, 00:00:08, Null0
D 155.1.5.0/24 [90/26905600] via 155.1.0.5, 00:00:18, Tunnel0
D 155.1.7.0/24 [90/26982400] via 155.1.0.5, 00:00:18, Tunnel0
D 155.1.8.0/24 [90/26931200] via 155.1.0.5, 00:00:18, Tunnel0
D 155.1.9.0/24 [90/27008000] via 155.1.0.5, 00:00:18, Tunnel0
D 155.1.10.0/24 [90/26956800] via 155.1.0.5, 00:00:18, Tunnel0
D 155.1.13.0/24 [90/26956800] via 155.1.0.5, 00:00:18, Tunnel0
D 155.1.37.0/24 [90/26982400] via 155.1.0.5, 00:00:18, Tunnel0
D 155.1.45.0/24 [90/26905600] via 155.1.0.5, 00:00:18, Tunnel0
D 155.1.58.0/24 [90/26905600] via 155.1.0.5, 00:00:18, Tunnel0
D 155.1.67.0/24 [90/26956800] via 155.1.0.5, 00:00:18, Tunnel0
D 155.1.79.0/24 [90/26982400] via 155.1.0.5, 00:00:18, Tunnel0
D 155.1.108.0/24 [90/26931200] via 155.1.0.5, 00:00:18, Tunnel0
D 155.1.146.0/24 [90/26931200] via 155.1.0.5, 00:00:18, Tunnel0

Why is it that the loopbacks have been all summarized to 1 summary route, but not the link between the Router have not been summarizes in the routing table? I've added the topology.

INE_Topology .jpg

INE_topology.jpg

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Comments

EdTheLad

Auto-summary will summarize prefixes that do not share the same major network of the egress interface. 155.1.x.x is the major network, 155.1.0.5 is the next-hop. So the 155.1.x.x prefixes don't get summarized.

FrankGuthrie

Hi Ed,

Then why did it create a summary route for the 155..1.0.0/16? Is this to advertise to the other Router. Because it has the more specific Route already?

EdTheLad

FrankGuthrie wrote: »

All the routers in the network have EIGRP turned on without summary. After auto-summary is turned on, the output looks like this:

Has auto-summary been turned on, on all routers or just r2?

FrankGuthrie

EdTheLad wrote: »

Has auto-summary been turned on, on all routers or just r2?

On all of them.

The goal was to see what was happening of auto-summary is used on older versions of IOS, as auto-summary is turned on, not anymore on 15.x.

Monkerz

I cannot see the topology (too small on my phone), but I would guess you are consistently using subnets of supernet 155.1.0.0/16 for router interconnects. If so, are those "glue-networks" contiguous throughout? See what I am getting at here?

Also, can you upload a bigger diagram? Placement within the network is relevant as well.

EdTheLad

EIGRP is creating a summary to null for all major eigrp networks in the rib. You are not receiving the more specific prefixes for 150.1.x.x from the tunnel neighbor because the tunnel neighbor has auto-summary enabled. As i said before, the tunnel interface is 155.1.x.x, the more specific prefixes with major net 155.1.x.x do not get summarized, this is a rule.
The idea behind the summary to null is to stop route feedback, rip unfortunately doesn't have the same feature.

FrankGuthrie

Added the topology.

Going through the replies to understand what is happening as I still can't see it.