BGP advertisement.

[tushar47]

Dear sir,

I am working in Class A ISP. Can i advertise IP Pool less then 256 IPs in BGP.

ie. /25 prefix instead of /24 prefix IP Pool.

Regards,

Ashu

[mhussein]

Hello,

I don't know if there is a clear cut answer. Most service providers filter prefixes longer than 24, e.g NEN http://www.newedgenetworks.com/about/legal/bgp4.php So if you advertise a /25, there is a very good chance that it will be blackholed somewhere upstream.

That being said, there are actually /25 and /26 prefixes making the round, e.g AS10026. Try any of the route-servers at www.traceroute.org and use "sho ip bgp cidr-only | inc /25" to investigate.

Your best bet is to check with your peer/upstream to find out what thier policy is.

HTH,

Mustafa

[mcdonald.richards]

I can't think of any carriers that will accept advertisements longer than /24.

[ashok_boin]

Hi,

Yes, even big ISPs also allowing only up to /24. You need to work with your ISP to permit /25 but you cann't control your ISP's ISP OR the third party ISPs policies. I meant to say that even if you can convince your ISP to advertise, the next level ISP won't allow /25 to be advertised.

And also it's really not a good idea to advertise less than /24 prefixes in Internet as it is already crossed more than one lakh prefixes with existing routing policies.

Thank you,

-Ashok.