BGP advertisement and provider independent addresses

[jon_panes24]

hi,

if i have obtained a Provider indepent address lets say a /21, can I subnet it to really small block like /28 or /29 and advertise it via BGP to my service provider. Will my service provider allow those subnet size and propagate that block throughout the internet ?

thanks and regards,

jonathan

[milan.kulik]

Hi, I'm afraid most of ISPs would not accept such a small prefix. AFAIK, usually /24 is the smallest prefix accepted generally. I.e., even if you agree with your particular ISP he will accept /28s, some upstream ISPs might drop such small prefixes. Why do you need to advertise such small prefixes? Do you want to connect multiple small sites to the Internet? In that case I'd try to agree with your ISP he will accept those small prefixes from your sites but for sure I'd also advertise the whole /21 from your main site, e.g. If upstream ISPs would drop the small prefixes they will still accept your /21 and the traffic for your small sites would be still delivered to your ISP as routed to your /21. And your ISP would know the detailed routing for your /28s. Best regards, Milan