[c-nsp] BGP and IP

[Jon Lewis]

On Tue, 14 Sep 2004, James Hampton wrote:

> We will soon be setting up a BGP session with GBLX, but are in the
> middle of an IP migration phase. We currently have an ARIN /19 which
> we are migrating to, but we have several other block in use that are
> from a previous provider(s) and are not Swiped to us. According to
> GBLX BGP policy we cannot advertise these old blocks.

Best solution is to get your old ISP to swip that space or if GBLX will
accept it, get an LOA from old ISP permitting you to announce those IPs to
other transit providers.  This is most likely just a safeguard at GBLX to
keep you from saying "sure a.b.c/20 is mine, please add it to my
prefix-list filter" when it's really someone else's space.

> The basic situation I am in is this; we will be dual homed
> non-transit, we have 2 address types, arin assigned blocks and old
> blocks (which are not swiped to us but are being advertised through
> another link). There is no way that I can see to tell our routers to
> send just our arin block traffic to the GBLX edge and all other
> traffic out the other link.

You could policy route it...but as long as each provider isn't doing uRPF
or other similar filtering, outgoing traffic picking the "wrong provider"
isn't an issue.  It'll still get where it needs to go.  It's just your
input traffic that'll be limited (old IP dest traffic only getting to you
via old ISP).  As each provider what kind of (if any) IP filtering they do
on your connection.  Ask them to be sure to allow traffic sourced from any
of your IP block...but you could run into the same problem with GBLX as
you did with BGP...if they actually do IP filter your connection.

----------------------------------------------------------------------
 Jon Lewis                   |  I route
 Senior Network Engineer     |  therefore you are
 Atlantic Net                |
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