Mutual Redistribution

Hi,

There is a provider who is running ISIS in its core and they
are using
RIP for the management interface. Is it valid to
redistribute all the
ISIS routes into RIP and all the RIP routes into ISIS?

Cant this create a loop or something?

Thanks,
Kent

On Tue, 28 Mar 2006 06:46:13 +0530
"Glen Kent" <glen.kentgmail.com> wrote:

> 
> Hi,
> 
> There is a provider who is running ISIS in its core and
they are using
> RIP for the management interface. Is it valid to
redistribute all the
> ISIS routes into RIP and all the RIP routes into ISIS?
> 

Depends on what they are trying to achieve, as well as their
routing
protocol topology. Mutual redistribution may not be
necessary if in one
of the routing protocol clouds they have a default route
pointing
towards the other e.g. for a a hub and spoke topology (IS-IS
hub, RIP
spokes), a default in the RIP cloud pointing towards the
IS-IS hub, and
then redistributing the RIP learned routes into IS-IS would
achieve the
same as what mutual redistribution is being used for.

> Cant this create a loop or something?
> 

You've just got to make sure that routes don't get
redistributed back to
where they came from e.g. an IS-IS route into RIP, then from
RIP back
into IS-IS, then IS-IS into RIP etc. On face value you'd
think that
increasing metrics would prevent this routing information
loop, except
during redistribution the metric can loose its ability to
properly
measure the path length, in part due to some protocols not
having very
large metric capacity (RIP probably being the only one). One
better
solution is to take advantage of route tags or labels. When
a route is
redistributed you tag it, and then when mutual
redistribution occurs in
the other direction, you exclude routes that have that tag.
You'd need
to do this in both redistribution directions, with different
tags to
prevent loops in either direction. This method doesn't rely
on the
behaviour of always increase metrics, so it would be more
robust.

HTH,
Mark.

-- 

        "Sheep are slow and tasty, and therefore must
remain constantly
         alert."
                                   - Bruce Schneier,
"Beyond Fear"

Mark Smith wrote:

> One better
> solution is to take advantage of route tags or labels.
When a route is
> redistributed you tag it, and then when mutual
redistribution occurs in
> the other direction, you exclude routes that have that
tag. You'd need
> to do this in both redistribution directions, with
different tags to
> prevent loops in either direction. This method doesn't
rely on the
> behaviour of always increase metrics, so it would be
more robust.
> 
> HTH,
> Mark.
> 
I dont believe popular vendors implementations of rip
propogate tags.

At least the last time I tried loop prevention with that, it
didnt work.

On Tue, 28 Mar 2006 16:37:48 -0500
Joe Maimon <jmaimonttec.com> wrote:

> 
> 
> Mark Smith wrote:
> 
> > One better
> > solution is to take advantage of route tags or
labels. When a route is
> > redistributed you tag it, and then when mutual
redistribution occurs in
> > the other direction, you exclude routes that have
that tag. You'd need
> > to do this in both redistribution directions, with
different tags to
> > prevent loops in either direction. This method
doesn't rely on the
> > behaviour of always increase metrics, so it would
be more robust.
> > 
> > HTH,
> > Mark.
> > 
> I dont believe popular vendors implementations of rip
propogate tags.
> 
> At least the last time I tried loop prevention with
that, it didnt work.

Did it happen to be RIPv1 ? Only RIPv2 supports route tags.

-- 

        "Sheep are slow and tasty, and therefore must
remain constantly
         alert."
                                   - Bruce Schneier,
"Beyond Fear"

Mark Smith wrote:
> On Tue, 28 Mar 2006 16:37:48 -0500
>
> 
> Did it happen to be RIPv1 ? Only RIPv2 supports route
tags.
> 
Of course it was rip2

Rip1 is dead. Anyone using it should be shot.

On Wed, 29 Mar 2006 06:33:08 -0500
Joe Maimon <jmaimonttec.com> wrote:

> 
> 
> Mark Smith wrote:
> > On Tue, 28 Mar 2006 16:37:48 -0500
> >
> > 
> > Did it happen to be RIPv1 ? Only RIPv2 supports
route tags.
> > 
> Of course it was rip2
> 
> Rip1 is dead. Anyone using it should be shot.

I don't know. If it solves the problem well enough, and you
don't have
any better alternatives, I think using it would be fine. 

-- 

        "Sheep are slow and tasty, and therefore must
remain constantly
         alert."
                                   - Bruce Schneier,
"Beyond Fear"