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what is the meaning of the tag keyword?

hanyawad
Level 1
Level 1

Hi,

i was reading a topic of redistribution and manipulation of the routing information and one of the requirements is to set a tag of 5 to  some routes through rout-map as in the following clauses:

route-map eigrp-into-ospf permit 18

  match ip address A-14-3-x-x

  set tag 99

so can any one please tell me what is the meaning of that tag, in other words in which situation the router will use that tag value?

Regards,

Makar

1 Accepted Solution

Accepted Solutions

Ryan Newell
Cisco Employee
Cisco Employee

Joseph is right! In your example the access-list with name A-14-3-x-x will be tagged with value of 99. And like Joseph said it is particularly helpful with preventing route feedback when dealing with mutual redistribution on multiple routers.

One customer I supported configured several static routes and a select handful were configured with a tag value. A route-map matched the tag value of the static routes to be redistributed into the enterprise.

R1(config)#ip route 1.1.1.1 255.255.255.255 2.2.2.2 tag ?

  <1-4294967295>  Tag value

ip route 4.4.4.4 255.255.255.255 5.5.5.5

ip route 1.1.1.1 255.255.255.255 2.2.2.2 tag 1

!

router ospf 1

redistribute static subnets route-map static-tag

!

route-map static-tag

  match tag 1

Tags like communities for BGP allow an IGP to make decisions on a group of routes.

Regards,

Ryan

View solution in original post

5 Replies 5

Joseph W. Doherty
Hall of Fame
Hall of Fame

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Posting

Tag has no meaning, per se. It's just a way of marking a route with a number you assign.  It can be very useful to quickly identify the source of a route in your routing table.

For example, say your redistribute one routing protocol into another, you can tag those injected routes with an identifier that would easily allow you to avoid redistributing the injected routes back into the original routing protocol they came from (assist in dealing with mutual redistribution).

I've sometimes used it with redistributed static routes to identify the router that injected them into my routing protocol.

Ryan Newell
Cisco Employee
Cisco Employee

Joseph is right! In your example the access-list with name A-14-3-x-x will be tagged with value of 99. And like Joseph said it is particularly helpful with preventing route feedback when dealing with mutual redistribution on multiple routers.

One customer I supported configured several static routes and a select handful were configured with a tag value. A route-map matched the tag value of the static routes to be redistributed into the enterprise.

R1(config)#ip route 1.1.1.1 255.255.255.255 2.2.2.2 tag ?

  <1-4294967295>  Tag value

ip route 4.4.4.4 255.255.255.255 5.5.5.5

ip route 1.1.1.1 255.255.255.255 2.2.2.2 tag 1

!

router ospf 1

redistribute static subnets route-map static-tag

!

route-map static-tag

  match tag 1

Tags like communities for BGP allow an IGP to make decisions on a group of routes.

Regards,

Ryan

hanyawad
Level 1
Level 1

thanks Joseph and Ryan for your helpful information.

Best Regards,

makar

Just curious...are you reading CCIE routing and switching cert guide? It looks like an example from that book. If so are you pursuing your CCIE?

Ryan

that is right, yes i'm

do you have any recommendations for me to pass the written exam?

thanks

Makar

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