Redistribute command

Unanswered Question
Mar 15th, 2007

router ospf 7

router-id 192.168.250.9

redistribute connected subnets tag 9

network 172.16.9.0 0.0.0.255 area 0

In the above config, what's the meanning of "tag 9" in redistribute cmd line?

I have this problem too.
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Harold Ritter Thu, 03/15/2007 - 08:10

The purpose of this command is to tag the routes redistributed into ospf with a value of 9. This value can later be used to filter these same routes.

Hope this helps,

v-tang Thu, 03/15/2007 - 08:51

Is the 'tag' function mean the Layer 3 header is mapped into a fixed length, unstructured value to speedup the routing decision?

And I still not understand the value of 9 use for. How about I set it to 7. What's the different?

Jon Marshall Thu, 03/15/2007 - 08:55

Hi

There isn't a difference between using 7 or 9. It is a number you choose to use. You can then match against this number on other routers to make decision about how to handle routing updates etc.

I believe the tag label will be part of the OSPF header ie. a value that has a field in the header.

HTH

Jon

Richard Burts Thu, 03/15/2007 - 08:58

One other point: Victor's question seems to assume that the tag is used in the routing decision (perhaps to speed up the routing decision). That is not the case. The tag does not enter into the routing decision. It is simply a way to identify the route so that a route map somewhere can identify those routes and take some action based on the value of the tag.

HTH

Rick

b.henshaw Sat, 03/17/2007 - 07:10

Route tagging is nothing to do with the Layer 3 header. It won't have any appreciable impact on routing decisions unless you're using route maps which match on tag.

The tag is part of the OSPF message and is just an arbitrary value which you choose. If you don't know what it is, you probably don't need to use it.

jason.plank Sat, 03/17/2007 - 07:02

it's pretty simple, you tag routes so that you can filter or manipulate them elsewhere. Pretty common to do in enviroments where you have multiple entrance points to routing domains or have multiple routing protocols running and multiple redistribution points. When you configure a route-map one of the match options is tag, meaning all routes that match "whatever the tag is" set "whatever you want to set".

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