Lab 106 - BGP Filtering using Prefix-List

Lab 106 - BGP Filtering using Prefix-List
Di Posting Oleh : Simple Learning
Kategori : BGP Core Technologies Routing

Prerequisites: CCNP level skills.

Topology

Pic. 1 - Topology Diagram.
Icons designed by: Andrzej Szoblik - http://www.newo.pl

Task 1
On R4 check what prefixes are originated by AS 50.

Task 2
On R4 filter out the following:
  • Class A prefixes shorter than /24
  • Class C prefixes longer than /27
Use prefix-list to accomplish this.

    Solution

    Task 1
    On R4 check what prefixes are originated by AS 50.

    The command to use: show ip bgp regexp _50$

    Pic. 2 - BGP Table on R4
    (prefixes originated by AS 50)

    Task 2
    On R4 filter out the following:
    • Class A prefixes shorter than /24
    • Class C prefixes longer than /27
    Use prefix-list to accomplish this.

    The following should be filtered out:
    Class A prefixes shorter than /24 = 5.5.0.0/16
    Class C prefixes longer than /27 = 200.55.55.0/29

    R4 Configuration:
    !
    ip prefix-list MATCH_TASK_2 seq 5 deny 0.0.0.0/1 le 23
    ip prefix-list MATCH_TASK_2 seq 10 deny 192.0.0.0/3 ge 28
    ip prefix-list MATCH_TASK_2 seq 15 permit 0.0.0.0/0 le 32
    !
    router bgp 124
     no synchronization
     bgp router-id 172.16.104.4
     bgp log-neighbor-changes
     network 172.16.104.0 mask 255.255.255.0
     network 172.16.144.0 mask 255.255.255.0
     neighbor 10.1.14.1 remote-as 124
     neighbor 10.1.14.1 route-reflector-client
     neighbor 10.1.14.1 prefix-list MATCH_TASK_2 in
     neighbor 10.1.24.2 remote-as 124
     neighbor 10.1.24.2 route-reflector-client
     neighbor 10.1.24.2 prefix-list MATCH_TASK_2 in
     no auto-summary
    !

    Verification:
    Pic. 3 - BGP Table on R4
    (prefixes originated by AS 50)

    The following prefixes have been filtered out:
    Class A prefixes shorter than /24 = 5.5.0.0/16
    Class C prefixes longer than /27 = 200.55.55.0/29

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