Troubleshooting Leak-maps

For basics about leak-maps read >>http://networkqueen.blogspot.com/2011/01/leak-maps.html

If your Leak-map is not configured incorrectly, one of two things can happen:

1. If the leak-map keyword is configured to reference a nonexistent route map, the configuration of this keyword has no effect. The summary address is advertised, but all component routes are suppressed.
   
2. If the leak-map keyword is configured, but the access list does not exist or the route map does not reference the access list, the summary address and all component routes are sent

These are both easy mistakes to spot. Always double check to make sure the summary and the leak-map are doing exactly what they are supposed to do.

Leak-maps

A leak-map is a method of using a route-map.
It can be helpful to use a leak-map to "leak" in or only allow certain routes to the stub. The benefit of route leaking (advertising a route) is that the leaked route is more specific than a summarized route and is therefore the preferred route.

Consider the example below:

Routers A,B, C and stub are participating in the same EIGRP AS.
Notice that past router A and B, the addresses can be summarized as a /23 (as noted above.)
So, we can summarize these routes by adding the following command on A and B on the interfaces facing router c:
 Router(config-if)#ip summary-address eigrp 100 192.168.0.0 255.255.254.0

So what does this mean for router C?
Without any special configuration (without any leak-maps configured), that would mean that router C would see two paths to the route 192.168.0.0 /23 with an equal cost.

What if you wanted to force the routers to prefer taking router A to get to the stub LAN (192.168.1.0/24)?
This is where the leak map comes in handy.
By putting the leak-map on router A, and "leaking" just that 192.168.1.0/24 as well as the summary route, we can ensure that router C will prefer that path.

To do this add the following in router A instead of the summary address command above. There are a few steps to getting this work:

1. An ACL is required to restrict the address you want to "leak"
2. A route map is required to match the ACL
3. the leak map parameter has to be added to the summary address command.

These are the commands needed:
RouterA(config)#access-list 1 permit 192.168.1.0 255.255.255.0
RouterA(config)#route-map LEAK-STUB-LAN permit
                               #match ip address 1
RouterA(config)#int fa0/0
RouterA(config-if)#ip summary-address eigrp 100 192.168.0.0 255.255.254.0 leak-map LEAK-STUB-LAN


So what else can you do with a leak-map?

Another alternative method of using a leak-map (which i believe is less commonly known) is using as part of
Router(config-router)# eigrp stub connected leak-map <LEAK-MAP>
As you probably know, "eigrp stub connected" command permits EIGRP to advertise the directly connected routes. However, by using the leak-map command, you can "leak" non directly connected network on the stub.

Troubleshooting Leak Maps>> http://networkqueen.blogspot.com/2011/01/troubleshooting-leak-maps.html
info source: http://www.cisco.com/en/US/docs/ios/12_3t/12_3t14/feature/guide/gt_esflr.html