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RE: router startup behavior

  • From: Steve Naslund
  • Date: Mon Jan 14 15:09:47 2002


Sorry, didn't get your first message clear in my head.  The next question I
would have is what do the routes look like.  To get that many routes for a
couple
of class Cs, the router's BGP must be really broke.  I would try to look at
router
type and software version and see if there is a correlation there.  I would
then try
Cisco's web site to see what the known BGP issues are for that IOS version.
The bug
toolkit has a lot of resolved BGP bugs but you need to know the version and
platform
in order to get a better search.  You usually need a support contract to get
to this
area but you might be able to talk them into helping you or having one of
the service
providers submit the problem as a trouble case.

Can you provide a sample of the routing table during the bad advertisements
?

Steve
> -----Original Message-----
> From: Stephen J. Wilcox [mailto:steve@opaltelecom.co.uk]
> Sent: Monday, January 14, 2002 1:53 PM
> To: Ratul Mahajan; Steve Naslund
> Subject: RE: router startup behavior
>
>
>
> that doesnt fit with the sequence of events outlined below
>
> ie
> reboot
> 1000+ routes appear
> 1000+ routes removed
>
> you are saying
>
> line failure
> 1000+ routes removed
> line recovery
> 1000+ routes appear
>
> and the numbers ie 1-1000 seems very high for this small provider with one
> or two class Cs at a maximum
>
> On Mon, 14 Jan 2002, Steve Naslund wrote:
>
> >
> > Here is my best guess as to what you are seeing.  Most likely a
> large CIDR
> > block is announced
> > by a service provider A.  A small CIDR block is given to a
> customer who is
> > connected to multiple
> > service providers and thus running BGP.  Now the more specific route is
> > announced by service provider B,
> > he does not own the block but is announcing it on behalf of
> service provider
> > As customer.  What is happening is that the customer has a line
> or router
> > failure and that withdraws their more specific announcement from service
> > provider B.  Since the service provider A is announcing a
> supernet route he
> > now becomes the only route
> > for that block.
> >
> > +++++++++++++++++++++++++++++++
> > Steven Naslund
> > Network Engineering Manager
> > Hosting.com - Chicago
> > +++++++++++++++++++++++++++++++
> >
> > > -----Original Message-----
> > > From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu]On Behalf Of
> > > Ratul Mahajan
> > > Sent: Monday, January 14, 2002 12:54 PM
> > > To: nanog@merit.edu
> > > Subject: router startup behavior
> > >
> > >
> > >
> > >
> > > at university of washington, we are doing a measurement study of bgp
> > > misconfiguration
> > > (http://www.cs.washington.edu/homes/ratul/bgp/index.html).
> > >
> > > one of the things we found is that there are a lot of announcements of
> > > more-specifics that come and go within a matter of 2-5 minutes.
> > >
> > > by talking to the operators involved in these incidents, we found that
> > > most of these are caused when the router is rebooted (intentionally or
> > > not). while some operators were aware of this side effect,
> most were not,
> > > and were taken by surprise that they just injected anywhere
> from 1-1000
> > > routes into BGP only to withdraw them a couple of minutes later.
> > >
> > > i would like to understand this behavior better. is this behavior
> > > vendor-specific (cisco?) or pervasive? is there a
> configuration style that
> > > causes or avoids this "spill-over"?
> > >
> > > my understanding is limited to this happens when the bgp
> session comes up
> > > too soon, before the filters have taken effect. could someone familiar
> > > with router internals shed some light on it?
> > >
> > > the problem is limited to route origination only, or also propagation?
> > > in other words, can a router propagate a route it should not while
> > > starting up because export filters are not yet in place?
> > >
> > > never ever gotten my hands dirty into router configuration; your input
> > > would be invaluable.
> > >
> > > thanks,
> > > 	-- ratul
> > >
> > >
> >
> >
>
> --
> Stephen J. Wilcox
> IP Services Manager, Opal Telecom
> http://www.opaltelecom.co.uk/
> Tel: 0161 222 2000
> Fax: 0161 222 2008
>
>





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