From: Baety Wayne SrA 18 CS/SCBX (Wayne.Baety@xxxxxxxxxxxxx)
Date: Mon Jun 10 2002 - 03:01:05 GMT-3
Another problem with distribute-list is its inherent inability to
distinguish routes of differing prefix length. Let's say you want to allow
121.1.0.0/24 through but not 121.1.0.0/16. Any access list style wildcard
you create that matches one route will match the other. BGP handles this
situation quite nicely with its prefix-list capability, however. For the
moment, Route-Tagging is the only successful way to deal with heterogeneous
masking, BGP support notwithstanding. But as you've already pointed out,
some protocols do not support tagging of routes.
WAYNE BAETY, MCSE, SRA, USAF
Network Systems Trainer
> -----Original Message-----
> From: Anthony Pace [mailto:anthonypace@fastmail.fm]
> Sent: Monday, June 10, 2002 9:36 AM
> To: Tom Larus; Treptow, Georg; Dennis Laganiere; 'Paul Connelly';
> ccielab@groupstudy.com
> Subject: Re: OSPF tags as a way to stop route feedback from
> redistribution-- what is the downside?
>
> The downside of the distribute lists is that networks can't really be
> added behind the redist router (if you used permits in the
> dist-list)They also destroy redundany accross multiple redistribution
> points. Doyle describes a scenario where you don't block the routes
> being fedback (perhaps form a second redist-router), but lower their AD
> so they never make it into your routing table and thus are never
> advertised beyond the redist router. If there is a failure somewhere
> then these routes with their "inferior" AD will be prefered and go into
> the table and once the network converges you have a redundent path.
>
> Anthony Pace
>
> On Sat, 8 Jun 2002 22:07:34 -0400, "Tom Larus" <tlarus@novacoxmail.com>
> said:
> > Yes. RIP does not carry tags. This tagging must be done as the routes
> > are
> > redistributed INTO a routing protocol that supports them. I see the
> > problem, now, and that is that we still need to stop the OSPF routes
> > that go
> > into RIP or IGRP from feeding back into OSPF. For that I guess we need
> > to
> > use the old methods of blocking individual routes.
> >
> > Doyle I also indicated that distribute lists have their shortcomings,
> > too,
> > but it is too late for me to get teh book and cite the page. He had an
> > explanation that I need to take a bit more time to think about and
> > digest. I
> > definitely need to do more work with this manipulating admin distance.
> > The
> > big problems seem to have to do with redistributed routes that have
> > lower
> > admin distance.
> >
> >
> > ----- Original Message -----
> > From: "Treptow, Georg" <gxtrept@qwest.com>
> > To: "'Tom Larus'" <tlarus@novacoxmail.com>; "Anthony Pace"
> > <anthonypace@fastmail.fm>; "Dennis Laganiere"
> > <dennisl@advancedbionics.com>;
> > "'Paul Connelly'" <chewy7700@yahoo.com>; <ccielab@groupstudy.com>
> > Sent: Saturday, June 08, 2002 9:42 PM
> > Subject: RE: OSPF tags as a way to stop route feedback from
> > redistribution--
> > what is the downside?
> >
> >
> > > This unfortunatly is not an answer but more of an extension to Tom's
> > > question.....
> > >
> > > I have recently done a lot of work on tagging, one of my scenarios
> that I
> > > tried did not work out that great..
> > >
> > > R1--------------R6----
> > > RIP v.1 |
> > > | OSPF
> > > R10--|
> > > |
> > > R4--------------R13---
> > >
> > > R1,R4 are redistribution routers between RIP v.1 and OSPF, R10 runs
> RIPv.1
> > > only. R6 and R10 OSPF only.
> > >
> > > I thought to myself that there has to be a better way of
> redistribution
> > from
> > > RIP to OSPF and vice versa.
> > > Instead of doing distribute/prefix lists I tagged all routes going
> into
> > the
> > > RIP domain (from OSPF) at R1 with 1111 and R4 I used 4444.
> > > At R1 I declared all routes with a tag of 4444 to be dismissed from
> > > redistribution back into OPSF and at R4 i did the same blocking all
> routes
> > > with a tag of 1111 but allowing all others. For whatever reason all
> routes
> > > from the RIP domain were blocked.
> > >
> > > Is it possible that RIP gets rid of tag information? Am I missing
> > something
> > > here?
> > >
> > >
> > > Thanks,
> > >
> > > Georg Treptow
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: Tom Larus [mailto:tlarus@novacoxmail.com]
> > > Sent: Saturday, June 08, 2002 8:21 PM
> > > To: Anthony Pace; Dennis Laganiere; 'Paul Connelly';
> > > ccielab@groupstudy.com
> > > Subject: OSPF tags as a way to stop route feedback from
> redistribution--
> > > what is the downside?
> > >
> > >
> > > I'd like to ask about the downside of another approach that seems too
> good
> > > to be true. In doing practice labs, I like to tag routes from other
> > > protocols as they are redistributed into OSPF (for example, tag routes
> > from
> > > IGRP 120 with tag 120), then have a route-map that stops those routes
> from
> > > going back into the other protocol. The problem is that one does not
> see
> > > this in case studies or in practice lab solutions very often, and that
> > makes
> > > me nervous. Doyle I contains a reference to this use of tags in the
> > chapter
> > > on route-maps, and that makes me feel a little better.
> > >
> > > This has the feel of something that seems neat but is very dangerous.
> > > Basically, anything that does involve manually typing in half the
> routes
> > in
> > > my network feels wrong, because it is not the tedious method that
> involves
> > > as much typing of routes as possible and nailing things down manually.
> > > --- Original Message -----
> > > From: "Anthony Pace" <anthonypace@fastmail.fm>
> > > To: "Tom Larus" <tlarus@novacoxmail.com>; "Dennis Laganiere"
> > > <dennisl@advancedbionics.com>; "'Paul Connelly'"
> <chewy7700@yahoo.com>;
> > > <ccielab@groupstudy.com>
> > > Sent: Saturday, June 08, 2002 8:01 PM
> > > Subject: OSPF into IGRP and summarizing into FLSM
> > >
> > >
> > > > Tom Larus said "Let's say you have loopback addresses on OSPF
> enabled
> > > > routers that you will need to summarize so that an IGRP /24 network
> > > > will be able to see them and reach them. You redistribute them into
> > > > OSPF, and use summary-address ip mask to summarize them right there
> on
> > > > the same router, which is by definition an ASBR because
> redistribution
> > > > is happening on it. Works like a charm."
> > > >
> > > > In other words you are using IP SUMMARY under OSPF even though you
> want
> > > > to shoot the /24 into IGRP? Then, a /24 is created right there on
> that
> > > > router and puhed into the IGRP world? Is that correct?
> > > >
> > > > I have been looking at this list for a definitive answer on this for
> a
> > > > while (not wanting to repost a question if it has allready been
> > > > answered) This seems like a solution. The quesion has been asked
> many
> > > > times and interpreted or missinterpreted differently in different
> posts
> > > > but essentially this is the problem as I see it: All of the
> protocoles
> > > > on the LABS we have all been doing have a mechanism for
> redistributing
> > > > and controlling summarization except IGRP. The LABS almost always
> give
> > > > you the ability to summarize almost all your networks via these
> other
> > > > mechanisms long before they reach the OSPF/IGRP redistribution point
> > > > with the exeption of a loopback or directly connected network on
> that
> > > > router which does not conform to the IGRP FLSM. It has been
> suggested
> > > > that a "ip default-network" be shot into IGRP and this works but it
> is
> > > > questionable as to weather this constitutes an ILLEGAL STATIC ROUTE.
> > > > The Solie labs pose this scenario but the soltions do not address
it.
> > > >
> > > > Are there any other tools that can be used?
> > > >
> > > > Anthony Pace
> > > >
> > > >
> > > >
> > > > On Tue, 4 Jun 2002 13:35:53 -0400, "Tom Larus"
> <tlarus@novacoxmail.com>
> > > > said:
> > > > > I have never taken the lab, so I could not speak to that aspect of
> the
> > > > > question, but I did learn something recently I thought was neat,
> but
> > > > > that
> > > > > many others here have probably known for years.
> > > > >
> > > > > Let's say you have loopback addresses on OSPF enabled routers that
> you
> > > > > will
> > > > > need to summarize so that an IGRP /24 network will be able to see
> them
> > > > > and
> > > > > reach them. You redistribute them into OSPF, and use summary-
> address
> > > > > ip
> > > > > mask to summarize them right there on the same router, which is by
> > > > > definition an ASBR because redistribution is happening on it.
> Works
> > > > > like a
> > > > > charm.
> > > > >
> > > > > Okay, it's old hat for a lot of you old hands, but I still think
> it is
> > > > > pretty neat.
> > > > >
> > > > >
> > > > > ----- Original Message -----
> > > > > From: "Dennis Laganiere" <dennisl@advancedbionics.com>
> > > > > To: "'Paul Connelly'" <chewy7700@yahoo.com>;
> <ccielab@groupstudy.com>
> > > > > Sent: Tuesday, June 04, 2002 12:40 PM
> > > > > Subject: RE: Connected routes vs network statement
> > > > >
> > > > >
> > > > > > Some routing protocols will interpret the two differently.
> EIGRP,
> > or
> > > > > > instance, will see the redistributed route as external, which
> has a
> > > much
> > > > > > higher AD.
> > > > > >
> > > > > > --- Dennis
> > > > > >
> > > > > >
> > > > > > -----Original Message-----
> > > > > > From: Paul Connelly [mailto:chewy7700@yahoo.com]
> > > > > > Sent: Tuesday, June 04, 2002 9:03 AM
> > > > > > To: ccielab@groupstudy.com
> > > > > > Subject: Connected routes vs network statement
> > > > > >
> > > > > > Is there a preference in the lab when to use "redistribute
> > connected"
> > > vs.
> > > > > > network statements? I know the redistribute connected will not
> turn
> > on
> > > the
> > > > > > routing protocol on the interface but you can easily turn it off
> > with
> > > > > > passive-interface. Just want to check if the exam wants you to
> do it
> > a
> > > > > > certain way.
> > > > > >
> > > > > >
> > > > > >
> > > > > > Thanks
> > > > > >
> > > > > >
> > > > > >
> > > > > > ---------------------------------
> > > > > > Do You Yahoo!?
> > > > > > Sign-up for Video Highlights of 2002 FIFA World Cup
> > > > > >
This archive was generated by hypermail 2.1.4 : Tue Jul 02 2002 - 08:12:30 GMT-3