[j-nsp] Conditional Advertisemet?

[Harry Reynolds]

Not aware of any fixes for this particular issue in that book....but its
been a while since I looked at it. ;)

The scenario there was a bgp peer address (1.0.1.1) that resolved
initially through a default route, but once the session comes up we
learn a 10.0/16, which encompasses the bgp peering address, and is more
specific than the default that was initially used to resolve bgp peering
address. In this case we hide the 10.0/16 because installing it would
negate use of default route (more specific) and using  a /16 learned
over a bgp peering session to resolve the route to *that* bgp peering
address could be bad.



Regards, Harry

 

> -----Original Message-----
> From: Mellott, Eric [mailto:mellotte at netcsc.com] 
> Sent: Thursday, October 05, 2006 1:13 PM
> To: Dale Gregory; Harry Reynolds; Chuck Anderson
> Cc: juniper-nsp at puck.nether.net; Berkheimer, Tim; Smith, Chris
> Subject: RE: [j-nsp] Conditional Advertisemet?
> 
> Yeah, this is exactly the problem I am running into and 
> didn't know if there were any options available other than 
> the generate route.  
>   
> Unfortunately, I don't have the JNCIP book handy, but will 
> see if I can find it.  
> 
> Thank you for the responses.
> 
> -Eric
> 
> 
> -----Original Message-----
> From: Dale Gregory [mailto:dalegreg at centurytel.net]
> Sent: Thursday, October 05, 2006 4:01 PM
> To: Harry Reynolds; Chuck Anderson; Mellott, Eric
> Cc: juniper-nsp at puck.nether.net
> Subject: Re: [j-nsp] Conditional Advertisemet?
> 
> Harry, I am sure you remember this since you wrote the book, 
> ;-) but your JNCIP book on pg 530 says, "newer versions of 
> JUNOS software will not allow a more specific route to 
> recurse through a less specific route because this behavior 
> could lead to recursion loops."
> 
> Eric, on pgs 530-538 & 573-579 there are several listed 
> options and explanations on how to deal with situations like 
> this that may help you out.
> 
> Dale
> 
> 
> At 02:33 PM 10/5/2006, Harry Reynolds wrote:
> >Hmm. Normally a generate/aggregate route is activated by a
> more-specific
> >route, i.e., contributing prefix.
> >
> >In this case you are trying to activate a more specific 
> generated with
> a
> >less specific contributing route, which I do not think will 
> work. The 
> >forwarding NH of a generated route is determined by the FNH of the 
> >preferred contributing route. Forwarding for a /28 over a /16 could
> lead
> >to loops.
> >
> >
> >Regards
> >
> >
> > > -----Original Message-----
> > > From: juniper-nsp-bounces at puck.nether.net
> > > [mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of Chuck 
> > > Anderson
> > > Sent: Thursday, October 05, 2006 12:19 PM
> > > To: Mellott, Eric
> > > Cc: juniper-nsp at puck.nether.net
> > > Subject: Re: [j-nsp] Conditional Advertisemet?
> > >
> > > On Thu, Oct 05, 2006 at 01:59:17PM -0400, Mellott, Eric wrote:
> > > > Have a BGP configuration where I learn a /16 network 
> from one eBGP 
> > > > neighbor and want to advertise a subset of that network,
> > > i.e. a /28,
> > > > to a different eBGP neighbor.  Currently, I am able to
> > > advertise the
> > > > subnet by configuring a static route which puts the /28 
> in table, 
> > > > however; this kills anything dynamic.  Is there a way with
> > > conditional
> > > > advertisements or a generate route to dynamically advertise the
> /28
> > > > upon receipt of the /16?  Also, I don't want to rely on the BGP 
> > > > neighbor (who is advertising the /16) to give me the 
> /28 instead.
> > >
> > > This might work:
> > >
> > > [edit routing-options]
> > > # show generate
> > > route w.x.y.z/28 policy MATCH-16;
> > >
> > >
> > > [edit policy-options]
> > > # show policy-statement MATCH-16
> > > term 1 {
> > >     from {
> > >         route-filter w.x.0.0/16 exact;
> > >     }
> > >     then accept;
> > > }
> > > term 2 {
> > >     then reject;
> > > }
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