North American Network Operators Group

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BGP filtering policies, UU, and you

  • From: David Barak
  • Date: Tue Apr 09 15:32:12 2002

Hi Henry et al,

There's no real problem with your current space. 
Assume for the minute that each of your offices has a
UU T1.  You announce the chunks of your /22 through
your various T1s, and that announcement (along with
the UU/14) is passed along to UU customers and peers. 
Verio will ignore the /22, but will direct traffic to
UU because they will accept the /14.  so no problem
there.  The only possible issue is this:
assume one T1 to UU and one to <non-Verio provider>. 
UU T1 goes down, therefore /22 withdrawn there, /22
announcement through <provider> becomes only route. 
Verio ignores this, and directs traffic to UU (via the
/14), and UU will then direct traffic to <provider>
because UU has very liberal routing policies.  So in
the worst case, you could get some sub-optimal
routing, but nothing particularly bad, and Verio is
the only substantive ISP who still uses these filters
(AFAIK).

The bigger issue in that case would be getting the UU
line up faster :)

-David Barak
"Quis custodes ipsos custodiet?" - Juvenal


Henry Yen wrote:
We were recently assigned a /22 from UUNet in
conjunction with some
transit we're buying from them.  The space is inside
their superblock,
65.242.0.0/14.  We are concerned that our route
announcement of this
block would be filtered out by some other providers,
as it's not
class C/swamp space (or even class B space for that
matter).
Verio's current policy, for one, indicates that this
would be so.

This is of particular concern to us as our little
network encompasses
several physical partially-meshed locations, with a
mix of varying
bandwidths both upstream as well as intra-location. 
Traffic Engineering
is what we think is a reasonable (business) approach
to address our
flexibility needs, and so we're trying to move to
address space(s) that
would be least likely to be BGP filtered.

We've asked for a different block from UUNet but the
request didn't
meet with success; UUNet suggested that any problems
encountered
as a result of this allocation could probably solved
by e-mailing
any NSP whose traffic interchange with us might be
negatively
affected (unlikely, to be sure, but still...), and
would then
change their filter (I'm unconvinced of this
scenario).

I briefly browsed the NANOG archives, and didn't see
this issue discussed
recently.  Have the BGP filtering policies for "most"
ISP/NSP's been
relaxed to the level of "accept /24's from class A
(ARIN-allocated) space"?
Am I mis-reading Verio's posted policy?  Is there
anyone from UUNet
who might choose to comment?  Is there something else
I'm misunderstanding?


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