Leak Map - Eigrp, Some leaks are useful..


Jul 10, 2012 7:08 AM
Sep 23rd, 2011

Route leaking is a technique which is used together with summarization. It is used in the situations where we want to save memory by summarizing routes but still want some routes to be preffered over others for some reasons. Leak map reffernces an access-list and whatever network is permitted in the access-list will be leaked along summary route.

Topology and addressing scheme:

Leak map.jpg

R1 has two point-to-point sub-interfaces going to frame-relay cloud connecting it to R2 and R3 respectively:

serial 1/0.12 :

serial 1/0.13 :

it also has three loopback interfaces:

loo 1 :

loo 2 :

loo 3 :

R2 has one point-to-point interface going to frame-relay cloud connecting it to R1

serial 1/0.21 :

R3 has one point-to-point interface going to frame-relay cloud connecting it to R1

serial 1/0.31 :

Eigrp has already been configured with summarization off on these routers. If you want to see the configuration it is attached with this blog.

Case 1: From R1, we want to advertise summary route and network attached to loopback 2 to R2:

Before we start, lets run a quick check. Lets have a look at Router 2 routing table:

R2 ip route.png

After configuring summarization on R1

R1#config t

Enter configuration commands, one per line.  End with CNTL/Z.

R1(config)#int se 1/0.12

R1(config-subif)#ip summary-address eigrp 100


*Mar  1 00:17:48.083: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor (Serial1/0.12) is resync: summary configured

The routing table of R2 will look like this:


Now, if we want R2 to have the summary address plus the network for loopback 2

We can use leak-map and here is how we use it:

On R1, the advertising router:

We will first create an access-list matching network for loopback 2

R1(config)#access-list 1 permit

then we will create a route-map matching this access-list

R1(config)#route-map R1-2 permit

R1(config-route-map)#match ip add 1


Now, remove the ip address under int se 1/0.12 connecting R1 to R2

R1(config)#int se 1/0.12

R1(config-subif)#no ip add

You will see the neigbors going down

*Mar  1 00:22:33.531: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor (Serial1/0.12) is down:

Now, we will create the virtual template interface

R1(config-subif)#int virtual-template 12

R1(config-if)#ip add

And, write the summary address command under it with leak map

R1(config-if)#ip summary-address eigrp 100 lea

R1(config-if)#$address eigrp 100 leak-map R1-2

Lastly, apply the virtual template interface to serial sub-interface

R1(config-if)#int se 1/0.12

R1(config-subif)#frame-relay interface-dlci 102 ppp virtual-template 12

This completes the configuration at R1

Now, lets go to R2 where we only need to configure a virtual-template interface:

R2(config)#int se 1/0.21

R2(config-subif)#no ip add

R2(config-subif)#int virtual-template 21

R2(config-if)#ip add

R2(config-if)#int se 1/0.21

R2(config-subif)#frame-relay interface-dlci 201 ppp virtual-template 21

At this point, you will see the adjaceny going up using virtual interface:

R2#sh ip eigrp neighbors

IP-EIGRP neighbors for process 100

H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq

                                            (sec)         (ms)       Cnt Num

0               Vi2               11 01:03:25  331  1986  0  15

R1#sh ip eigrp neighbors

IP-EIGRP neighbors for process 100

H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq

                                            (sec)         (ms)       Cnt Num

1               Vi2               11 01:04:43  325  1950  0  11

0               Se1/0.13          10 01:21:11  535  3210  0  5

Now, lets have a look at routing table of R2:


Case 2: From R1, we want to advertise summary route and all specific addresses to R3:

Lets configure R1 first:

R1(config)#route-map R1-3 permit 10

This time we have just created a route-map and not reffered any access-list. When this is done, then summary and all the

specific routes are advertised.

We will see how will it look like.

On R1, next we will create virtual template and associate it with the interface.

R1(config)#int se 1/0.13

R1(config-subif)#no ip add


*Mar  1 00:35:19.679: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor (Serial1/0.13) is down: interface down


R1(config)#int virtual-template 13

R1(config-if)#ip add

R1(config-if)#ip summary-address eigrp 1 leak-map R1-3


R1(config)#int se 1/0.13

R1(config-subif)#frame-relay interface-dlci 103 ppp  virtual-template 13

Again, on R3 we will create virtual template just as we did on R2 in last example:

R3(config)#int se 1/0.31

R3(config-subif)#no ip add


R3(config)#int virtual-template 31

R3(config-if)#ip add


R3(config)#int se 1/0.31

R3(config-subif)#frame-relay interface-dlci 301 ppp virtual-template 31

Lets now check if we achieved what we wanted:


And what we see is that we have the summary address and the specific routes as well.

So, all leaks are not harmful some help us as well..

Overall Rating: 5 (3 ratings)
kedaisal Tue, 11/01/2011 - 00:02

Nice One Pulkit

pnagpal Tue, 11/01/2011 - 06:00

Thanks Hameed!



lvyongjia0043 Wed, 11/16/2011 - 04:56


Very helpful.

A good way to solve the route leak problem in eigrp!

I got it , thank you !

pnagpal Wed, 11/16/2011 - 05:31

Thanks Yongjia!



biswadeepmajumder Thu, 12/29/2011 - 11:06

Excellent... very helpful

pnagpal Tue, 01/17/2012 - 04:41

Thanks Biswadeep.



Vinayaka Raman Tue, 07/10/2012 - 07:08

I have a scenario like I wanted to advertise a summary route through tunnel interface...But I wanted a subset of summary route to be denied..is it possible ?


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Posted September 23, 2011 at 7:39 AM
Comments:7 Overall Rating:5

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