Eigrp Topology

[parthrawat979]

I didn't understand the summarization part and how it's possible that only two routers R1 and R2 have the summarized route for R6's loopback??

[Enes Simnica]

@parthrawat979 good question G. Summarization is done where u configure it, at the border interface, so only routers upstream of that border see the single summarized prefix. Routers inside the summarized area still keep and advertise the specific /32s or /30s.

and the question is, why only R1 and R2 see the summary? Well whoever is “upstream” from the routers where u put the summary will receive the summarized route. If R3 or R5 are configured to summarize R6’s networks toward R2 (or toward the R1/R2 side), then R2 (and anything beyond R2 like R1) will only receive the summary. R3/R5 and their directly connected neighbors still keep the specific routes locally. Lets say that on the interface toward R2 u add a summary for Eigrp:

int toward-R2
 ip summary-address eigrp 12345 56.0.0.0 255.255.255.0

use commands like show ip route to see the summarized entry. AND show ip eigrp topology to see what each neighbor is advertising

SOO: Summarization means combining several specific routes into one larger network prefix to make the routing table smaller and simpler.

check this: https://www.geeksforgeeks.org/computer-networks/how-to-configure-eigrp-summarization-in-cisco/

and hope it helps!

-Enes

[paul driver]

Hello
First of all the task objective states to use delay to accomplish the 56.1.1.0/0 and 12.1.1.0/30 path manipulation, I believe using a offset list applied to the least preferred path rtr is a good alternative

As for the eigrp summaries These will be applied to a specific direct neighbour, as such only that neighbour and its own neighbouring eigrp peers will receive the summary.

Based on your topology and the task objective, rtr2 will receive dual summaries from rtr3-rtr4 and rtr1 will receive a single summary from rtr2.

So from a rtr2 perspective it will have dual summary paths to reach those rtr6 loopbacks, which can be further manipulated if desired to use a specific path via applying a simple summary metric applied to either to rtr3-4 eigrp router process

[elwin-berrar]

Hi

To add to what Enes and Paul explained, EIGRP summarization works outbound. The router advertises the summary only on the interface where you configure it, which is why only R1 and R2 see the summarized route for R6’s loopback. The summary is generated in that direction, not learned from it.

Routers closer to R6 still keep the detailed prefixes because EIGRP doesn’t replace local routes with summaries. The goal is simply to reduce the size of the routing table for devices farther from the source. You can confirm where the summary is applied with:

show ip protocols
show ip route | include summary