Leak Map - Eigrp, Some leaks are useful..

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Sep 23, 2011 7:39 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 : 10.1.12.1/24

serial 1/0.13 : 10.1.13.1/24

it also has three loopback interfaces:

loo 1 : 1.1.0.1/24

loo 2 : 1.1.1.1/24

loo 3 : 1.1.2.1/24

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

serial 1/0.21 : 10.1.12.2/24

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

serial 1/0.31 : 10.1.13.3/24

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 1.1.0.0 255.255.252.0

R1(config-subif)#

*Mar  1 00:17:48.083: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.1.12.2 (Serial1/0.12) is resync: summary configured

The routing table of R2 will look like this:


2.png

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 1.1.1.0 0.0.0.255

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

R1(config-route-map)#exit

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 10.1.12.2 (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 10.1.12.1 255.255.255.0

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

R1(config-if)#ip summary-address eigrp 100 1.1.0.0 255.255.252.0 lea

R1(config-if)#$address eigrp 100 1.1.0.0 255.255.252.0 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 10.1.12.2 255.255.255.0

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   10.1.12.1               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   10.1.12.2               Vi2               11 01:04:43  325  1950  0  11

0   10.1.13.3               Se1/0.13          10 01:21:11  535  3210  0  5

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

nh.png

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

R1(config-subif)#

*Mar  1 00:35:19.679: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 10.1.13.3 (Serial1/0.13) is down: interface down

R1(config-subif)#exit

R1(config)#int virtual-template 13

R1(config-if)#ip add 10.1.13.1 255.255.255.0

R1(config-if)#ip summary-address eigrp 1 1.1.0.0 255.255.252.0 leak-map R1-3

R1(config-if)#exit

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-subif)#exit

R3(config)#int virtual-template 31

R3(config-if)#ip add 10.1.13.3 255.255.255.0

R3(config-if)#exit

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:

4.png

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..


Average Rating: 5 (2 ratings)

Comments

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

great!

Very helpful.

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

I got it , thank you !

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
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