BGP multihome

[nharinathka]

Hi,

Need help from all,

Is it possible to advertise single IP or /27 subnet in internet. As I know, only /24 pool or less (/23, /22, 21 etc.. ) should be advertise into internet.

Scenario :  I have two internet link from two ISP and planning to buy /24 pool from APNIC. I wanted to choose one /27 pool subnet to be reacble via Link B. and rest all IPs via Link A. Also if any one link fails than it should be reachble via other link and vice-versa.

Example:

I have IP pool as 1.1.1.0/24.

Two Links :  Link-A & Link-B

1.1.1.0/27 should use LINK-B as primary path

Rest all IP subnets ( 1.1.1.32/27, 1.1.1.64/26, 1.1.1.128/25 ) should use Link-A as primary path.

If any link fails, all subnet should be reacble via next link.

[robert.falconer]

I've never worked with an ISP that will allow anything but /24 or shorter. You can call ISP A and ask if they'll do it.

[Mahesh Gohil]

Hi,

Instead of taking /24 ask for /23 from apnic and divide in two /24 and then advertise to each ISP.

If I am not wrong Apnic will charge equal amount for /24 or /23 due to fact that they charge for management and not per ip pool. (please cross check with apnic).

The ISP do not permit >/24 is because of two reason.

1/ If they accept /25 or /27 they have to advt. /24 pool (owned by you ) with source as their own AS which leads to blacklisting of AS.

2/ upstream of ISP do not allow these small brackets to help internet bgp table to keep at lower volume.

Regars

Mahesh