Lab 107 - BGP Aggregation using IP Route Null0

Prerequisites: CCNP level skills.

Topology

Pic. 1 - Topology Diagram.

Icons designed by: Andrzej Szoblik - http://www.newo.pl

Task 1
Configure R5 so that it advertises one summary route representing the below prefixes (loopbacks on R5). Make sure the summary route does not overlap any other addresses. Do not use 'aggregate-address' command.

• 55.5.0.0/24
• 55.5.1.0/24
• 55.5.2.0/24
• 55.5.3.0/24

Solution


Task 1 

Configure R5 so that it advertises one summary route representing the below prefixes (loopbacks on R5). Make sure the summary route does not overlap any other addresses. Do not use 'aggregate-address' command.

R5 Configuration:

!

ip route 55.5.0.0 255.255.252.0 Null0

!

router bgp 50
 no synchronization
 bgp router-id 172.16.105.5
 bgp log-neighbor-changes
 network 5.5.0.0 mask 255.255.0.0
 network 55.5.0.0 mask 255.255.252.0
 network 172.16.105.0 mask 255.255.255.0
 network 200.5.5.0 mask 255.255.255.224
 network 200.5.5.32 mask 255.255.255.224
 network 200.55.55.0 mask 255.255.255.248
 neighbor 10.1.35.3 remote-as 30
 no auto-summary

!

Verification:

Pic. 2 - BGP Table on R4.

Notice!
BGP cannot advertise prefixes that do not have EXACT match in the routing table. The 'ip route null0' can be used to summarize the prefixes. Only local prefixes can be advertised this way.