Re: Route redistribution

Hey Marcin,

In the example you posted, the tags are set as part of the redistribution.

"router ospf 1
redistribute eigrp 100 subnets tag 390"

That statement sets anything redistributed into ospf from EIGRP with a tag
of 390. If you have the lab going right now, try doing "show ip route
x.x.x.x" for a subnet that was redistributed from EIGRP into OSPF. You
should see the tag 390 on it.

Like Dale said, the idea is to keep routes from being looped between IGP's
with multiple phyiscal paths between them.

Take a look at the route-maps in the configs you posted. Notice how theres
the deny statement first, then the permit statement second?

The router is saying "I'm going to set my tag to 390, but I know theres
another router out there setting it to 890. And since I already know those
routes, I Dont want to learn them from him" The other router is doing the
opposite.

Chris

On Sun, Jun 7, 2009 at 9:33 PM, Marcin Zgola <MZgola_at_netrixllc.com> wrote:

> yeah, but confusion is that route-map matched 890 and 390, but 890 and
> 390 were not defined any where before in workbook/lab.
>
> If they were how can I look up route tags?
>
>
>
> Marcin Zgola
> Internetwork Lead
> MCSE, CCNA, CCSP, CCIE #18676
> Netrix, LLC
> http://www.netrixllc.com
> Ph. 847-964-5300
> Fax.: 847-964-5350
>
>
> -----Original Message-----
> From: Dale Shaw [mailto:dale.shaw_at_gmail.com]
> Sent: Sunday, June 07, 2009 9:12 PM
> To: Marcin Zgola
> Cc: ccielab_at_groupstudy.com
> Subject: Re: Route redistribution
>
> Hi Marcin,
>
> On Mon, Jun 8, 2009 at 11:34 AM, Marcin Zgola <MZgola_at_netrixllc.com>
> wrote:
> > I am confused with "match tag" I know you can tag the routes and stuff
> > but what is 890 or 390. Where these values came from? How can I look
> > these up?
>
> EIGRP is being redistributed into OSPF on two devices. Device "A" is
> setting tag 390, and device "B" is setting tag 890. These values are
> completely arbitrary. All routes that are redistributed will be tagged
> with those values and propagated through the routing domain.
>
> To ensure that original EIGRP routes redistributed into OSPF are not
> redistributed again into EIGRP, a route-map is used on each device to
> filter routes learned from the other device.
>
> e.g. device "A" does NOT redistribute routes marked with device B's
> tag of 890, and device "B' does not redistribute routes marked with
> device A's tag of 390.
>
> This is a loop prevention mechanism.
>
> Anyway, I think the key point for you is that these values are
> arbitrary and not based on any pre-defined standard. Not all protocols
> have a tag field and therefore not all protocols support tagging. Both
> EIGRP and OSPF support 32-bit tag values (0-4294967295).
>
> cheers,
> Dale
>
>
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Received on Sun Jun 07 2009 - 21:40:25 ART