BGP aggregation

Unanswered Question
Apr 27th, 2010
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Guys i have two subnets as under and i want to aggregate them in BGP but dont know what

would be the aggregation address if someone plz help me out....secondly i have to put ip prefix list as well for these networks so what would be that like le 32 etc


192.68.72.160 /27

192.68.72.32 /28

Thanks guys

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Giuseppe Larosa Tue, 04/27/2010 - 07:13
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Hello Khan,


you need to write down in binary the last byte and you need to find out the last matching bit in base addresses


160 = 128 +32  ->  1010 0000

32                         0010 0000


the only possible aggregate that covers both IP prefixes but also other possible prefixes is:


192.168.72.0/24   because first bit of 4th byte is different in the two base addresses


this is called a non exclusive summary route


in BGP you can use

router bgp xx

aggregate-address 192.168.72.0 mask 255.255.255.0


if this is not acceptable for you, you should advertise the IP single subnets


Hope to help

Giuseppe

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