Same AS number from different location and Migration of IP addresses

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1

Hello,

Is that okay to use Same AS number for the two different site on different
location?
as well as any good documentation or link or deployment scenario where I can
find the merging of two different AS into one AS?
As well as what to do if I have an IP addresses as a service provider
dependent block and want to migrate IP addressing to the IANA assigned ip
addresses?
how can i achieve that?

regards
Devang Patel

2

Hi Devang,

a good start point is the Internet Routing Architecture book:
http://www.ciscopress.com/bookstore/product.asp?isbn=157870233X

Regards,
Diogo

3

(I'm sending from a non text-only system at the moment, sorry.)

   These should help on the merging part.

   [1]http://www.cisco.com/en/US/docs/ios/12_4/ip_route/configuration/guid
   e/hbgpdas.html
   [2]http://www.cisco.com/univercd/cc/td/doc/product/software/ios122s/122
   snwft/release/122s25/fsbgpdas.htm
   [3]http://www.cisco.com/en/US/docs/ios/12_2t/12_2t11/feature/guide/ft11
   bhla.html

4

Hello,

Is that okay to use Same AS number for the two different site on different
location?

To answer this specific question, Autonomous Systems should be topologically convex.
This means, at the Internet interdomain routing (BGP) level, that packets
cannot leave an AS in one place to get to locations in the same AS in some other place.

So, to put two sites on one AS, there should be an internal connection between them, which can be done
through your internal network, by a direct connection, or by a tunnel. Traffic might come to
the AS at either site, and has to be routed internally to get to the other.

See RFC 1930 and the material linked to in the other posts.

Regards
Marshall

5

I am afraid I have to disagree with Marshall.

The idea behind an AS when the routing protocols were written long ago may have been a contiguous domain, but there are lots of things the protocols did not originally envision.

If you have two islands, and they each have a prefix which is globally routable, there is nothing wrong with the two islands sharing a single ASN. Island A announces Prefix A, and Island B announces Prefix B. Routing is done by prefix, not ASN, so there is no fear of Island A getting packets for Island B, and therefore no requirement for internal connectivity. And before anyone says anything about Island A not having connectivity to Island B, these are obviously not "transit free" networks, so each island can just point default. In fact, cisco even has a knob to listen to paths with your own ASN in it so you can do this without default (although I'm not sure I'd recommend that).

It works fine and saves the community from burning an ASN.

6

Patrick,

Your usage is quite consistent with the RFC 1930 guidelines on the use of
AS, which probably does need some updating but does have an operational
rather than a protocol theory viewpoint.

Specifically, an AS is defined not as a business entity, not as a routing
domain, but as:

   "...a connected group of one or more IP prefixes run by one
       or more network operators which has a SINGLE and CLEARLY DEFINED
       routing policy."

In this case, the sites have a common, coordinated routing policy. I do
agree that practicality does call for them to have a direct connection, but
otherwise, they meet the requirement of being one or more IP prefixes run by
one or more operators.

I do hope they register their routing policy, with appropriate comments.

Howard

7

sure it is. the magical anycast, used by many for DNS service delivery
oes exactly this.

--bill

8

Hi,

So if I will have the globally unique IP addresses for both the site which
are located at different location then its perfectly fine to use the same as
number in for same organisation having two different site located at
different location...right!!!

regards
Devang Patel

9

devang patel wrote:

So if I will have the globally unique IP addresses for both the site which
are located at different location then its perfectly fine to use the same as
number in for same organisation having two different site located at
different location...right!!!

Right.

But as others have stated you will have to do some configuration in order for the two locations to communicate *with each other*.

There are a a few different ways to accomplish this as has been discussed previously.

10

ascii art:

    (==== Internet =====)
      > >
  192.0.2.10 192.0.2.10
      > >
    AS-0 AS-0
      > >
  256.0.0.0 256.0.0.0

works a treat (as Joe Abley mentions as well).
--bill

11

Hi,

Yes I do have link between two sites so I will configure routing accordingly
so communication between two sites will follow that link...

regards
Devang Patel