How to configure EIGRP Summarization

ReneMolenaar · December 22, 2016, 12:29am

This topic is to discuss the following lesson:

system · May 16, 2013, 6:31pm

Hello Rene,

I have a question regarding ip summary-address command in above lesson.
By applying ip aummary-address command in fastethrnet 2/0 interface,
how come heart router know about the summary address.
As my understanding ip summary address is per interface basis.
I should apply ip summary-address in fastethernet 1/0 interface.
Would you correct me and help me to understand better.

Thanks.

ReneMolenaar · May 24, 2013, 9:43am

Hi Toral,

I just changed the picture because the interface number didn’t match. You configure a summary outbound on an interface facing towards your EIGRP neighbor.

Rene

system · August 21, 2013, 11:22am

Simple but effective workout to understand EIGRP summerizing

ReneMolenaar · August 28, 2013, 2:09pm

Thanks Django!

system · October 11, 2013, 9:28pm

thanks for the nice lesson, keep up the good work

oscaritox2000 · November 23, 2015, 10:56pm

Rene, why is it /23 mask? when I see the first statement showing /24.

Spade(config)#&lt;strong&gt;interface fastEthernet 2/0&lt;/strong&gt;
Spade(config-if)#&lt;strong&gt;ip summary-address eigrp 1 172.16.0.0 255.255.254.0&lt;/strong&gt;

1st. statement.

Hearts#&lt;strong&gt;show ip route eigrp
172.16.0.0/24&lt;/strong&gt; is subnetted, 2 subnets
D &lt;strong&gt;172.16.0.0&lt;/strong&gt; [90/30720] via 192.168.12.1, 00:02:28, FastEthernet0/0
D &lt;strong&gt;172.16.1.0&lt;/strong&gt; [90/30720] via 192.168.12.1, 00:02:28, FastEthernet0/0

Is it to cover 172.16.1.0 ?

Thanks,
Oscar

ReneMolenaar · November 24, 2015, 1:22pm

Hi Oscar,

That’s right, 172.16.0.0/23 covers both 172.16.0.0/24 and 172.16.1.0/24.

Rene

ethel_13mx · December 1, 2015, 6:39pm

Hello Rene,

Can you show us more examples using summarization? it’s an easy topic but I would like to see another scenarios

Thanks!!!

ReneMolenaar · December 3, 2015, 2:14pm

Hi Diana,

Sure, anything particular you would like to see?

Rene

azaadafghan · February 8, 2016, 1:14am

Hey Rene,

I am alittle confused with summarization over here. So taking your example over here, when we want to summarize subnets we used /23 subnet mask that is shared by all the subnets that we want to summarize and use it on interface level. But in your next lesson “no auto summarization” when we disable the “no auto summarization” we use wild card mask under eigrp configuration, what is the difference, why didn’t we use wild card mask over here ?

Best,

Tooryalai

ReneMolenaar · February 9, 2016, 5:34pm

Hi Tooryalai,

This can be confusing yes. Cisco isn’t very consistent with their usage of wildcards, subnet masks and CIDR notation. Sometimes it doesn’t make much sense

Rene

purohit.am · September 11, 2016, 5:08am

Hi Rene,

I have a doubt , how does summarization prevents the SIA issue ?
or in other words how does the neighbor knows not to send the query packet to this neighbor which is summarizing addresses to me !

thanks,

andrew · September 13, 2016, 7:02pm

Amit,
Only on the router where the summarization is configured does the Query process stop–not on the router that originates the Query. So for example, if you have three routers A, B, and C with a topology of A—B---C. B has created a summary, say 10.10.0.0/16. Suppose Router A has a route 10.10.10.0/24 that goes active. Router A will still send the Query message to B, but B will see that 10.10.10.0/24 is contained within its own configured summary of 10.10.0.0/16. This will cause Router B to stop propagation of the Query to router C. Additionally, Router B will reply immediately back to A’s Query saying “Unreachable”

ryllise1234 · October 31, 2016, 3:31am

Hey,

Has anyone tested this in GNS3?
Can’t seem to get it working

R1
interface Loopback0
 ip address 192.168.1.1 255.255.255.0
!
interface Loopback1
 ip address 192.168.2.1 255.255.255.0
!
interface FastEthernet0/0
 ip address 1.1.1.1 255.255.255.252
 ip summary-address eigrp 1 192.168.0.0 255.255.252.0 5
 duplex auto
 speed auto

router eigrp 1
 network 1.1.1.0 0.0.0.3
 no auto-summary

-

R2
interface FastEthernet0/0
 ip address 1.1.1.2 255.255.255.252
 duplex auto
 speed auto

router eigrp 1
 network 1.1.1.0 0.0.0.3
 no auto-summary

R2#show ip route
     1.0.0.0/30 is subnetted, 1 subnets
C       1.1.1.0 is directly connected, FastEthernet0/0
R2#

lagapidis · November 13, 2016, 5:26pm

Hello Ryan

I notice that in your show IP route command, no EIRGP routes show up. This tells me that for some reason, no EIGRP neighbours have been created. You should at least see the 192.168.1.0 and 192.168.2.0 subnets separately show up. Check the neighbour table to see that they have successfully created an adjacancy. Before you configure any EIGRP summarization, try to get EIGRP alone to function correctly. Then you can add the summarization commands.

I hope this has been helpful.

Laz

hamasferrer · November 14, 2016, 9:12pm

If the network is summarized, should not have an A.D of 5 in the neighbor routing table???

andrew · November 16, 2016, 2:42am

Hector,
No, it should not. The Administrative Distance of 5 for an EIGRP summary route is local only on the router that does the summarizing. When that summary is then advertised to a neighbor, the neighbor installs the summary with the regular AD of 90.

hamasferrer · November 16, 2016, 2:09pm

Hi Andrew,

Then, based on the exercise, it is in R1 where the route should appear with A.D. of 5.

R1#show ip route eigrp 
     172.16.0.0/16 is variably subnetted, 3 subnets, 2 masks
D       172.16.0.0/23 is a summary, 00:01:38, Null0

where we can check the A.D.?? Since it does not appear.

And thanks for ur reply

andrew · November 16, 2016, 2:21pm

Hector,
To check the AD of the route, issue:
#show ip route 172.16.0.0 255.255.254.0