BGP auto-summary and no autosummary

[sathyasav]

Hi,

Can any explain me the concept of BGP auto-summary and no auto-summary with some example because i went through some documents and it still confuses me a lot...

Thanks

Sathya

[Latchum Naidu]

Hi Sathya,

no auto-summary - tells BGP not to summarize IP addresses that you are advertising to neighbors as classful IP address boundaries.

BGP auto-summary rule says that ,Take a example that you are having network that 10.2.80.0/24 and you want to advertise into BGP with auto-summary,

So you need to advertise this network via network 10.0.0.0 in the bgp process with auto-summary.you cannot adverise 10.2.0.0 mask 255.255.0.0.it will not work.

so your configuration would be (with auto-summary)

R2#
router bgp 100
no synchronization
bgp log-neighbor-changes
network 10.0.0.0
network 10.177.206.0 mask 255.255.255.0
neighbor 10.2.47.193 remote-as 200
neighbor 10.2.255.47 remote-as 100

Please rate the helpfull posts.
Regards,
Naidu.

[sathyasav]

Hi Latcham,

If i have a network 10.20.10.0/24 on the router and if i want to advertise this network only to the outside world through BGP then i want to turn on the auto-summary also.below see the configuration below.

eg,

under BGP process,

network 10.20.10.0 mask 255.255.255.0

auto-summary

if i configure like this,will it adviertise only this 10.20.10.0/24 n/w or the entire classful n/w?

And my second question is if i have a n/w 10.20.10.0/24,10.20.20.0/24 and 10.20.30.0/24

In this case i want to adverdise only these three n/ws with auto-summay and no auto-summary turned on.Please explain this with some example configuration.

AWATING FOR UR REPLY>>>

Thanks

SATHYA

[cadet alain]

Hi,

in first case it will advertise the 10.20.10.0/24 only, if you do network 10.0.0.0 then it will advertise the 10.0.0.0/8 only

as well as if you do a network 10.0.0.0 mask 255.0.0.0

In second case:

with no auto-summary and following network commands:

-network 10.0.0.0 ----> nothing goes into bgp table

-network 10.20.10.0 mask 255.255.255.0 ---> the correct network goes into bgp table

with auto-summary:

-network 10.0.0.0 ----> only 10.0.0.0/8 goes into bgp table

-network 10.20.10.0 mask 255.255.255.0 -----> only the subnet goes into bgp table

Regards.

Alain.

[sathyasav]

Thanks Alain,

So if i want to advertise all these individual n/ws then i have to type the below things under the router BGP rite

network 10.20.10.0 mask 255.255.255.0

network 10.20.20.0 mask 255.255.255.0

network 10.20.30.0 mask 255.255.255.0

no auto-summary

if i do this the BGp will advierdise this netwrok right.So i configure any subnet apart from this like 10.0.0.0 mask 255.0.0.0 or 10.20.0.0 mask 255.255.0.0 it will not advertise any thing while No auto-summary configured.Am i right?

[cadet alain]

Hi,

right.

Alain.

[sathyasav]

Thaks Alain!!!!!