Understanding the 'aggregate-address <> summary', BGP?

Answered Question
Apr 7th, 2009

Folks, can you clarify what the "aggregate-address <> summary" could do in this case? I already read the documentation but it is not clear to me.

(...)

ip prefix-list My_Prefix seq 65 permit 12.30.0.0/18 le 32

ip prefix-list My_Prefix seq 100 deny 0.0.0.0/0 le 32

!

route-map PROJ1_OSPF100_REDISTR permit 10

description limit NEWDEVICE advertisement

match ip address prefix-list My_Prefix

!

router bgp 80342

address-family ipv4 vrf PROJ1

no redistribute ospf 100 vrf PROJ1

redistribute ospf 100 vrf PROJ1 route-map PROJ1_OSPF100_REDISTR

aggregate-address 12.30.0.0 255.255.192.0 summary-only

exit

!

End

(...)

I have this problem too.
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Correct Answer by Giuseppe Larosa about 7 years 8 months ago

Hello Marlon,

the aggregate-address creates a summarized route 12.30.0.0 with mask 255.255.192.0 and it will suppress the component routes (summary-only)

The summary route is created if at least a component route exists in the BGP table.

In your case this can be the result of redistribution of OSPF into BGP

As you can see prefixes within 12.30.0.0/18 are accepted in the route-map used to redistribute OSPF routes into BGP (prefix-list)

Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Tue, 04/07/2009 - 10:48

Hello Marlon,

the aggregate-address creates a summarized route 12.30.0.0 with mask 255.255.192.0 and it will suppress the component routes (summary-only)

The summary route is created if at least a component route exists in the BGP table.

In your case this can be the result of redistribution of OSPF into BGP

As you can see prefixes within 12.30.0.0/18 are accepted in the route-map used to redistribute OSPF routes into BGP (prefix-list)

Hope to help

Giuseppe

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