Eigrp automatic summarization
Hi all,
Doing some work on EIGRP and automatic summarization. Does a router only summarize its own connected networks when automatic summarization is in place?
R1 <-> R2 <-> R3
If R1 advertises 7.7.7.0/24 to R2, from my labwork R2 wont summarize the route to 7.0.0.0/8 when it sends it to R3, as I would have expected?
Doing some work on EIGRP and automatic summarization. Does a router only summarize its own connected networks when automatic summarization is in place?
R1 <-> R2 <-> R3
If R1 advertises 7.7.7.0/24 to R2, from my labwork R2 wont summarize the route to 7.0.0.0/8 when it sends it to R3, as I would have expected?
Studying for CCNP (All done)
Comments
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EdTheLad
Member Posts: 2,111 ■■■■□□□□□□
In a word,YES!Networking, sometimes i love it, mostly i hate it.Its all about the $$$$ -
tech-airman
Member Posts: 953
kpjungle,Hi all,
Doing some work on EIGRP and automatic summarization. Does a router only summarize its own connected networks when automatic summarization is in place?
It depends. Is the connected network also a subnet of the classful network?R1 <-> R2 <-> R3
If R1 advertises 7.7.7.0/24 to R2, from my labwork R2 wont summarize the route to 7.0.0.0/8 when it sends it to R3, as I would have expected?
Do you have automatic summarization enabled on R1? -
EdTheLad
Member Posts: 2,111 ■■■■□□□□□□
It doesn't depend, this is an eigrp caveat, the connected network is not part of the same subnet.tech-airman wrote: »It depends. Is the connected network also a subnet of the classful network?tech-airman wrote: »Do you have automatic summarization enabled on R1?
If R1 had auto-summary enabled it would not send 7.7.7.0/24 to R2 it would send 7.0.0.0/8, the question is in regards to how R2 handles its summarization.Auto-summary is enabled on R2, R2 has a route 7.7.7.0/24 towards R1, the link between R2 and R3 uses a different classful network than 7.0.0.0, you would expect R2 is classfully summarize 7.7.7.0/24 due to the boundary at R3,but it doesnt because 7.7.7.0/24 is not a local network.Networking, sometimes i love it, mostly i hate it.Its all about the $$$$ -
kpjungle
Member Posts: 426
It doesn't depend, this is an eigrp caveat, the connected network is not part of the same subnet.
If R1 had auto-summary enabled it would not send 7.7.7.0/24 to R2 it would send 7.0.0.0/8, the question is in regards to how R2 handles its summarization.Auto-summary is enabled on R2, R2 has a route 7.7.7.0/24 towards R1, the link between R2 and R3 uses a different classful network than 7.0.0.0, you would expect R2 is classfully summarize 7.7.7.0/24 due to the boundary at R3,but it doesnt because 7.7.7.0/24 is not a local network.
Yep. That pretty much sums it up.
Heres another curveball I ran into with RIP (version 2):
R1 <-> R2
R1 does not summarize by default, but R2 is set to. R1 advertises its loopback0 of 192.168.1.0/26 to R2. (the link between R1 and R2 is still a different major net). What behavior would you expect R2 to conform to? My first guess was that it would actually summarize to 192.168.1.0/24 and send it back to R1 (split horizon prevents the SAME route going back to R1, but this is not the same route). This is not what occurs. But if you create a loopback interface on R2 in the same major net (192.168.1.0), such as 192.168.1.65/27, it will advertise it back to R1 as 192.168.1.0/24.
Interesting no?
Studying for CCNP (All done) -
kryolla
Member Posts: 785
The router that has multiple interfaces in two different major network is the router that does summarization.
Enhanced Interior Gateway Routing Protocol - Cisco SystemsStudying for CCIE and drinking Home Brew -
kpjungle
Member Posts: 426
The router that has multiple interfaces in two different major network is the router that does summarization.
Enhanced Interior Gateway Routing Protocol - Cisco Systems
True, for EIGRP. RIP behaves differently though. It will summarize even though it has no interfaces. It does not need a connected route of the same major net to summarize when crossing a boundary.Studying for CCNP (All done) -
kryolla
Member Posts: 785
yeah eigrp does it according to network boundary where rip does it as well but also across different subnetsStudying for CCIE and drinking Home Brew
