From: Phil (theccie@gmail.com)
Date: Fri Jun 04 2004 - 22:39:06 GMT-3
Let me see if I can put into words (you guys out there, help me out if
I say something wrong):
You really need route-maps if you have multiple redistribution points:
R1------R2
| |---------10.1.1.0/24
R3------R4
Let's assume R2-R4, R2-R1 and R4-R3 are running ospf only and R1-R3 is
running eigrp and redistribution for ospf and eigrp is happening in R1
and R3. R1 will first learn 10.1.1.0 from R2 and advertise it to R3.
R3 will also learn 10.1.1.0 from R4 and advertise it to R1. Because
eigrp has a better AD than ospf, R1 may think it has a better path to
10.1.1.0 via R3, on the other hand, R3 may think it has a better path
to 10.1.1.0o via R1. You have just created a routing loop.
The route-map will tag the route and when it gets to R3 from R1 and
vice-versa, it will block the route thus avoiding the loop.
Please note, the example above is just to give you an idea of what may
happen. There are several other ways to avoid loops, you can change
the AD, use distribute-lists, etc. I like the route-maps because I
find them easier to configure and I have used them even when they are
not needed.
Phil
On Fri, 4 Jun 2004 17:56:26 -0700, john matus <jmatus@pacbell.net> wrote:
>
> thanks phil, yes it certianly does help give me a bit more insite to the
> whole subject. sometimes i don't see the reason for a route-map, especially
> since you usually WANT all the routes to be redistributed.....seems a bit
> redundant in that sort of situation
>
> Regards,
>
> John D. Matus
> MCSE, CCNP
> 818.782.2061 office
> 818.430.8372 mobile
> jmatus@pacbell.net
>
>
>
>
> ----- Original Message -----
> From: "Phil" <theccie@gmail.com>
> To: "john matus" <jmatus@pacbell.net>
> Cc: "lab" <ccielab@groupstudy.com>
> Sent: Friday, June 04, 2004 5:37 PM
> Subject: Re: redistribution best practices...?
>
> > John,
> >
> > You can call me redistribution nuts, but I always use the route-maps,
> > even when they are not necessary:
> >
> > NO TAG:
> > (when redistributing with IGP that do not support Tags)
> >
> > access-list 1 permit 172.16.5.0 0.0.0.255
> > access-list 1 permit 172.16.56.0 0.0.0.255
> > access-list 1 permit 172.16.35.0 0.0.0.255
> > (RIPv1 routes)
> >
> > route-map only-rip permit 10
> > match ip address 1
> >
> > route-map no-rip deny 10
> > match ip address 1
> > route-map no-rip permit 20
> >
> > router igrp 10
> > redistribute ospf 5 metric 1 1 1 1 1 route-map no-rip
> >
> > router ospf 5
> > redistribute igrp 10 subnets route-map only-rip
> >
> > ----------------------------------------------------------
> >
> > TAG:
> >
> > route-map eigrp2ospf deny 10
> > match tag 110
> > route-map eigrp2ospf permit 20
> > set tag 90
> >
> > route-map ospf2eigrp deny 10
> > match tag 90
> > route-map ospf2eigrp permit 20
> > set tag 110
> >
> > router eigrp 100
> > reditribute ospf 5 metric 1 1 1 1 1 route-map ospf2eigrp
> >
> > router ospf 5
> > redistribute eigrp 100 subnets route-map eigrp2ospf
> >
> > HTH,
> >
> > Phil
> >
> >
> > On Fri, 4 Jun 2004 02:20:19 -0700, john matus <jmatus@pacbell.net> wrote:
> > >
> > > got a question regarding redistribution between igp's....
> > > when you redistribute between, say, ospf and rip on the topology below
> > >
> > > rip rip/ospf ospf
> > > ----R1--------------------------R2----------------------------R3---
> > >
> > > is it the norm to apply a route-map on R2 that would specifically permit
> > > routes from r1 or r3? for example, lets say you had a loopback address
> and an
> > > ethernet subnet attached to R1 under rip, should you configure r2 as
> follows?
> > >
> > > router ospf
> > > redistribute rip sub route-map rip2ospf
> > >
> > > route-m rip2ospf permit 10
> > > match ip address 1
> > >
> > > access-l 1 permit <lo0>
> > > access-l 1 permit <e0> ?
> > >
> > > it seems to me that you would only do something like this if you were
> > > specifically trying to avoid redistributing specific routes, but in the
> case
> > > that you are not denying any prefixes, what is the advantage, if any, by
> doing
> > > this <avoiding routing loops possibly?....something else?>
> > > i've always done my redistribution without the route-maps so i'm curious
> about
> > > the ideology <i'm using ipexperts lab manual tonight and they go
> route-map
> > > CRAZY!!!>
> > >
> > > thanks in advance for your input!
> > >
> > > Regards,
> > >
> > > John D. Matus
> > > MCSE, CCNP
> > > 818.782.2061 office
> > > 818.430.8372 mobile
> > > jmatus@pacbell.net
> > >
> > > _______________________________________________________________________
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