BGP announcement

[mehrdad]

Hi,

What's the advantage and disadvantage when we announce with BGP4 two subnets or the summarize of them?

for example :

- scenario 1

router bgp xxxxx

network 64.110.252.0 mask 255.255.252.0

.......

- scenario 2

router bgp xxxxx

network 64.110.252.0 mask 255.255.254.0

network 64.110.254.0 mask 255.255.254.0

.......

Regards,

M.Rad

[ruwhite]

Neither of these configurations will summarize a route. The first will advertise 64.110.252.0/22 if that route is in your table. The second would advertise 64.110.252.0/24 and 64.110.254.0/24 as two seperate routes, if both of them exist in your routing table.

The advantages of summarizing over not summarizing is going to depend on your situation. Most of the time, you would advertise more specifics if you're trying to pull traffic in towards one entry point, but "normal operation" would be to advertise as few routes as possible, to aggregate your routes. This might help explain where the more specifics would be used:

http://www.cisco.com/en/US/tech/tk365/tk80/technologies_configuration_example09186a00800945bf.shtml

:-)

Russ.W

[preddyi]

It depands on the senario you are going to use.

Basic diff is, when summerized route is advertized 64.110.252.0/22, over two /23 prefixes the entries in route table are going to be less in quantity.

If you are having single upstream and not multi homed, then I would suggest to go for summerized advertizement.

If you are having multihoming, then depands on factors like.

1.Available bandwidth to different AS peerings.

2.How you want shape the traffic pattern over multiple links.(Load sharing)

3.Primary and back up announcement(redundancy)