RE: [isp-bgp] BGP announcement question

["James Jun" <james@towardex.com>]

Well one thing you need to be worried about is communication between Sites A
and B. If you are using same AS number, BGP's loop detection will reject
hearing of Site B's prefixes/route announcements at Site A and vice versa.
(Though if you take last resort default route from your upstreams, that is
not exactly a problem with exception of lack of sufficient NLRI information
for diverse route selection)

You can overcome this by using 'allowas-in' on your transit neighbor
sessions to your uplink ISPs, but such hack should always be temporary and
be well documented as it can also create other event-specific problems for
networks with changing topology in the future.  Another option available to
overcome this without using that hack is to apply for another AS number from
ARIN.  ARIN policies do allow acquisition of more AS numbers if you have
different sites multihomed while maintaining their own routing policy (in
other words, disconnected island POP's multihomed to separate ISPs at each
location, not connected by a transport).

Lastly, you can also buy transport (which is costly or moderately ok
depending on locations involved) or setup a GRE tunnel if inter-site traffic
is minimal or manageable to handle through tunnel link.  In such case,
ensuring that your transit links can handle more than 1500 bytes of MTU
would help, as 1476 MTU based GRE tunnels are royal pain.

Regards,
james


-----Original Message-----
From: Jim Barstow [mailto:jimb-clec@dssitech.com] 
Sent: Wednesday, February 28, 2007 2:41 PM
To: isp-bgp@isp-bgp.com
Subject: RE: [isp-bgp] BGP announcement question

I am aware of this.. Site B is to be multihomed to help prevent this, as
currently a link from Site A to Site B is not yet feasible. 


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SmartTel Communications
Jim Barstow
Sr. Telecom Engineer
jimb@smarttelco.com
PO Box 367
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Suite E
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tel: (251) 224-0868
fax: (251) 224-0830
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