redistribution mpbgp into ospf (ce-pe) issue cause outage

Unanswered Question
Mar 15th, 2009

We integrate a new backbone into our network, this bb is running mb bgp,it is connected to the CEs through ospf, once we integrated the new backbone to the network all of the device started to show AS 100 (this AS is using for mp bgp) . after troubleshooting we notice that ospf is carrying in one tag AS information this happened due to bgp is redistribute into ospf (CE-PE), for the CE routers (7609) this tag is not big deal but all of the Nokia devices like Border Gateway start to use the information for this tag in ospf, this cause a big outage in the network.. the question is: it is possible to filter this tag??.. and the other question is.. it is a normal behaviour.. because this is ibgp we shouldn't able to see the AS into ospf, isn't it???

I have this problem too.
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Giuseppe Larosa Mon, 03/16/2009 - 05:59

Hello Paola,

it is normal to see a BGP route redistributed into OSPF tagged with the BGP AS number.

if this is a problem you can use a route-map:

route-map BGP-to-OSPF permit 10

! match commands if needed

set tag value

set tag ?

<0-4294967295> Tag value

use a value that doesn't disturb the network (that for example is filtered somewhere to avoid re-injection in another device)

then when you decide what to redistribute from OSPF into BGP if you have mutual redistribution use

route-map OSPF-to-BGP deny 10

match tag value

route-map OSPF-to-BGP permit 20

! other settings here

router ospf 10

red bgp 100 subnets route-map BGP-to-OSPF

Hope to help


paolagallegos Mon, 03/16/2009 - 20:21

Hi Giuseppe..

thanks for your replay..

the think is I need that route but I don't want to see the AS information in ospf because some of the devices connected to the CE like Border Gateway start to send AS 100 to other operators... we don't need to send this AS out to the network....this AS is only for MP-BGP I want to keep it inside to the Backbone... Do you know if there is a way to filter this information contained in OSPF?? or you know other way to avoid this???. My other question is about the AS information.. do you think MP-BGP should put AS information into ospf??? for EBGP I understand because this can avoid loops but for MP-BGP (this is only for inside to the bb just for VRF routing) why I need to redistribute this inforamtion??/ I hope you can help me with this ..and thanks so much again for your help

thanks a lot.

Giuseppe Larosa Tue, 03/17/2009 - 01:11

Hello Paola,

what you can do is to set a different route tag unrelated to AS 100.

unfortunately there is no route tag none command available.


You can think to set the route tag field to 0.

As I wrote in my first post it is normal to see a BGP AS number placed in the route tag field of an external OSPF route.

I don't think this changes with MP-BGP.

Paola, be aware that in any case a route tag is just a label, it doesn't mean that you are using BGP AS 100 for sure.

Real routing problems can arise if you use route-tag values to decide if and what to redistribute.

If I understood correctly this is not your case.

Hope to help


paolagallegos Tue, 03/17/2009 - 05:25

Hi Giuseppe,

Yap it works, thanks for the advise I configured: "no set tag".. and it deleted all information for AS100..

So thanks again for that...

I am still concern about the AS100 information.. anyway..

I really appreciate your help.. thanks thanks thanks thanks so much....

God Bless you




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