BGP AS# & Public IP assignment query for Gurus..:-)

Unanswered Question
Feb 23rd, 2008

Hello BGP gurus,

need some clarification on BGP AS# & Public IP space assignments...

If Ripe assigns me a public ip block of, then..

1.Can I use individual subnets (, etc..) any where in the world as long as my ISP at that place is advertising them..?

2. Also, at those places, incase if I want to advertise my individual subnet via ISP BGP peering, (use BGP for redundancy, load balance via 2ISPs) do I have to request for seperate AS# at each location ..?

3.If I know a AS#, how do I find out, to whom that AS# is assigned to.

4. When RIPE assigns public block, will it also assign AS# or it need to be seperately requested...?

Thats all for now.

Thank you in advance.


I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 3 (1 ratings)
bvsnarayana03 Sun, 02/24/2008 - 00:02

1. yes u can use individual subnets as long as only those subnets are advertised by ur ISP & not the Summary.

2. not sure if same AS can be used at multiple locations. Lets see what experts have to say.

3. AS number registrations can be seen from IANA registry.

4. You need to purchase separate AS numbers separately.

hope that helps.

pls rate all helpful posts.

Danilo Dy Sun, 02/24/2008 - 00:19


1. Yes you can. You can even advertise an aggregated using your own AS# and advertise using another AS# (or your ISP AS#) in other part of the world. Because the more specific route still applies.

2. No need, you can advertised them using Private AS#, you just have to talk to your ISP to agree what Private AS# to use.

3. You can check from IANA or use the NICs WHOIS. ARIN, RIPE-NCC, APNIC, AFRINIC, LACNIC.

4. AFAIK they are seperate. The justification for both are different. Read their policy on IP Address block and AS# allocation.

[EDIT] Before you chop-chop your IP Address netblock, check with your upstream ISP (directly connected) the minimum number of netblocks they allow. Some ISP may allow /24 but some may not allow it.



mohammedmahmoud Sun, 02/24/2008 - 00:25


1. I believe so, but not more specific than /24, for more accuracy contact RIPE.

2. No, but you need some other BGP configuration considerations according to your case.

3. You can query the RIPE database at, just write the ASN in this format "ASXXXXX".

4. ASN and IP blocks are separately requested.

Finally you can contact RIPE at [email protected], for further details, they are very helpful.


Mohammed Mahmoud.

dongdongliu Sun, 02/24/2008 - 03:09


1. depends on your ISP whether would like to advertise trivial routing(more than 20 bit mask)

2. i`m not sure but i think one AS is enough

3. here we get the AS# from APNIC, i do not know there

4. yes,respectively



Mohamed Sobair Sun, 02/24/2008 - 10:18


1- Yes you can.

2- No you dont have to, You will need to have IBGP between your Edge routers.

3- you can Go to RIPE and find any information about AS's associated with Subnets and to whom its assigned.

4- I think you will need to request both , AS and Subnets, (Double check from RIPE).



fortis123 Thu, 02/28/2008 - 09:08

Thank you all for your replies. All replies are helpful .. :-)



This Discussion