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Re: ISP Filter Policies--Effect is what?
From: Kevin Gannon <kevin () gannons net>
Date: Tue, 08 May 2001 17:24:53 +0100



<snip>
Site                    BGP Advertisement       to      ISP
Amsterdam               169.61.201.0/24         AMSISP
Austin          169.61.111.0/24         Genuity & Internap
SanFran         169.61.119.0/24         Genuity & Internap
Tokyo                   169.61.202.0/24         TOKISP
Sydney          169.61.156.0/24         SYDISP

1. Since Verio says they would not accept /24 nets drawn from Class B space,
I assume this means that they don't insert a /16 into their tables so that
the /24 nets appear to Verio customers as unreachable. In this case, a
design
that wants to extend connectivity to verio customers (and any
other ISP with similar policies) must include a /16 advertisement from at
least
one of the sites.

2. Suppose a customer of a Verio-like ISP, wishes to go to ftp. foo.org. DNS
returns 169.61.201.155 (in amsterdam, see above). Verio passes the traffic
to the neighbor it received the /16 advertisement from. At this point, the
best thing that could happen
is if that neighbor has the /16 and /24 networks in its route table, right?
That
means, a path exists for that user to the amsterdam server and the only
problem
with routing to Amsterdam is that Verio possibly handed the traffic to a
sub-optimal
neighbor. Am I understanding this issue correctly?

Yes the logic seems clean , also another situation which might
happen is that Verio peers with ISP x and ISP x doesnt have a
specific /24 route they will follow a static to somewhere. You
want to be careful that the somewhere knows about the /24.
This could easily happen if Verio peers with the ISP that is
nearer and an ISP that also peers with this ISP. So verio
might decide hey the "longer" path is better and the packet
gets into the "longer" ISP and it wont have a /24 so it will
follow the /16.

Maybe if you could tell use who owns the addresses and how
big the original block is ? A whois points to a swiss bank is
this correct ?

I'm new to BGP. I've tried to get a handle on this issue on my own and by
working with Genuity, Internap and Cisco. No disrespect to those companies
but
each of them had this vague memory of Verio's policy but couldnt really tell
me
in plain language how it might affect the above scenario. Obviously, I
wasn't talking
to chief engineers. Someone from the CCIE mailing list suggested I browse
the archives of this list, which I did. But I didnt find a clear enough
answer to my questions--perhaps because they are too basic to be discussed
here or I'm not good at using this lists archive search engine.
Either way, any guidance on the above scenario is greatly appreciated.

-BM

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