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Forum Replies

  1. Rene what will happen if both router-map and access-list are deny?

    route-map NAME deny 10
    match ip address 1
    
    ip access-list standard 1
    deny 1.1.1.0
    permit any

    thanks!

  2. correction it's "route-map" not "router-map".

    sorry for typo

  3. Hi George,

    Sure, here's an example. We have a router that has learned some EIGRP routes on different interfaces:

    R1#show ip route eigrp 
    Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
           D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
           N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
           E1 - OSPF external type 1, E2 - OSPF external type 2
           i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
           ia - IS-IS inter area, * - candidate default, U - per-user static route
           o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
           a - application route
           + - replicated route, % - next hop override, p - overrides from PfR
    
    Gateway of last resort is not set
    
          2.0.0.0/32 is subnetted, 1 subnets
    D        2.2.2.2 [90/130816] via 192.168.12.2, 01:00:49, GigabitEthernet0/1
          3.0.0.0/32 is subnetted, 1 subnets
    D        3.3.3.3 [90/130816] via 192.168.13.3, 01:00:50, GigabitEthernet0/2
          4.0.0.0/32 is subnetted, 1 subnets
    D        4.4.4.4 [90/130816] via 192.168.14.4, 01:00:49, GigabitEthernet0/3
    D     192.168.23.0/24 [90/3072] via 192.168.13.3, 01:00:49, GigabitEthernet0/2
                          [90/3072] via 192.168.12.2, 01:00:49, GigabitEthernet0/1
    D     192.168.24.0/24 [90/3072] via 192.168.14.4, 01:00:49, GigabitEthernet0/3
                          [90/3072] via 192.168.12.2, 01:00:49, GigabitEthernet0/1
    D     192.168.34.0/24 [90/3072] via 192.168.14.4, 01:00:49, GigabitEthernet0/3
                          [90/3072] via 192.168.13.3, 01:00:49, GigabitEthernet0/2

    Let's enable a route-map that matches on interface Gigabit0/1 and attach it as a distribute-list:

    R1(config)#route-map ONLY_FIRST_GIG permit 10
    R1(config-route-map)#match interface GigabitEthernet 0/1
    
    R1(config)#router eigrp 1  
    R1(config-router)#distribute-list route-map ONLY_FIRST_GIG in

    Now the routing table looks like this:

    R1#show ip route eigrp 
    Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
           D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
           N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
           E1 - OSPF external type 1, E2 - OSPF external type 2
           i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
           ia - IS-IS inter area, * - candidate default, U - per-user static route
           o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
           a - application route
           + - replicated route, % - next hop override, p - overrides from PfR
    
    Gateway of last resort is not set
    
          2.0.0.0/32 is subnetted, 1 subnets
    D        2.2.2.2 [90/130816] via 192.168.12.2, 00:00:13, GigabitEthernet0/1
          3.0.0.0/32 is subnetted, 1 subnets
    D        3.3.3.3 [90/131072] via 192.168.12.2, 00:00:12, GigabitEthernet0/1
          4.0.0.0/32 is subnetted, 1 subnets
    D        4.4.4.4 [90/131072] via 192.168.12.2, 00:00:13, GigabitEthernet0/1
    D     192.168.23.0/24 [90/3072] via 192.168.12.2, 00:00:13, GigabitEthernet0/1
    D     192.168.24.0/24 [90/3072] via 192.168.12.2, 00:00:13, GigabitEthernet0/1
    D     192.168.34.0/24 [90/3328] via 192.168.12.2, 00:00:12, GigabitEthernet0/1

    There we go, only routes learned on Gigabit0/1 are accepted.

    Hope this helps.

    Rene

  4. andrew says:

    Derek,
    Route-Maps are the swiss-army knife of Cisco. You can use them for all kinds of things in many different ways depending on the situation. With EIGRP, access-lists, prefix-lists, and route-maps are all options of a distribute-list. In other words, the "distribute-list" keyword is entered first, then you can choose which option you want after. Check out the available options below:

    R1(config-router)#distribute-list ?
      <1-199>      IP access list number
      <1300-2699>  IP expanded access list number
      WORD               Access-list name
      gateway            Filtering incoming address updates based on gateway
      prefix             Filter prefixes in address updates
      route-map  Filter prefixes based on the route-map

    Now, without getting too deep, where you actually apply this depends on whether you are running EIGRP "classic" mode or EIGRP "named" mode (the new style, also called Multi-Address Family EIGRP).

    The example I showed above was from classic mode by going to the EIGRP process (let's just say, its Autonomous-System 1) by

    R1(config)#router eigrp 1

    If you are running named mode, it takes a little bit longer to get there. In the example below, I am running EIGRP Named Instance "NetLessons" with AS 1. Here are the commands to get to the right spot in this instance:

    R1(config)#router eigrp NetLessons
    R1(config-router)#address-family ipv4 unicast autonomous-system 1
    R1(config-router-af)#topology base
    R1(config-router-af-topology)#distribute-list ?
      <1-199>      IP access list number
      <1300-2699>  IP expanded access list number
      WORD               Access-list name
      gateway            Filtering incoming address updates based on gateway
      prefix             Filter prefixes in address updates
      route-map  Filter prefixes based on the route-map

    I hope I understood your question correctly.
    --Andrew

  5. Hi Rene,

    I have a quick question on EIGRP filtering in general. Say I have 3 routers, R1, R2, and R3 all running EIGRP and connected.

    R1 has 10.10.10.0/24 and 20.20.20.0/24
    If I want to advertise 10.10.10.0/24 only to R3 but not R2..
    From reading your lesson, I learned that I can apply a distribute-list acl in on R3 to block the advertisement of 10.10.10.0/24...

    Can this be done on R1 to filter outbound EIGRP advertisement of 10.10.10.0/24 only to R3 but not R2?

    Thanks!

    Barry

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