BGP dampening parameters

Unanswered Question
Jul 8th, 2009


juniper(customer end)-------cisco (my end noc)

i am facing problem while configuring bgp. its a ebgp link and the bgp state says Established but i am not getting the routes in my routing table but its coming as hidden route(unusable).

what could be the problem.

will it be due to bgp dampening parameters mismatch between juniper and cisco.

note my end dampening is not enbled in cisco 7000 series but in juniper dampening is enabled.

I have this problem too.
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Giuseppe Larosa Wed, 07/08/2009 - 05:21

Hello Hariharan,

>> table but its coming as hidden route(unusable).

Check the BGP next hop of these advertisements if it is unknown this is the problem

Hope to help


k.hariharan1 Wed, 07/08/2009 - 06:52

hi i dint get you.

let me make my question more clear.

i am working in isp. i had given a 5mb link to customer and customer end its juniper router j6350. bgp is running in his router , and they have their own AS number and ip blocks. so we r just advertising their ip block and AS via my upstream. meanwhile i had configured my cisco router to advertise only the default route to their end. This ebgp link is up and the bgp state is showing me established. but when i give sh route command in juniper router my default route is not reflecting , when i give sh route all , my advertised default route is showing me as unusable.

my set up is as follows

juniper(customer end)------> cisco my L3 switch ------> cisco(my Gw router)

cisco L3 conf:

just a default route for thier ip block pointing towards the nexthop as juniper end ip. L3 ospf is running and static routes are redistributed into ospf

my Gw conf:

router bgp 1880

neighbor 61.x.x.18 remote-as 4540

neighbor 61.x.x.18 description BMS

neighbor 61.x.x.18 ebgp-multihop 255

neighbor 61.x.x.18 update-source Loopback5

neighbor 61.x.x.18 version 4

neighbor 61.x.x.18 default-originate

neighbor 61.x.x.18 soft-reconfiguration inbound

neighbor 61.x.x.18 prefix-list bms in

neighbor 61.x.x.18 route-map bms-out out

and in the prefix list bms in

i allowed their ip blocks and deny remaining and in route map bms-out i had

i allowed only default route.


Hariharan k

Giuseppe Larosa Wed, 07/08/2009 - 11:14

Hello Harinan,

the J6350 acts also as a firewall so it is likely performing additional checks.

You need to find out the reason why the is not accepted.

I'm not sure but it may be checking if you advertise an IP prefix where the BGP next hop is contained.

This is just a wild guess.

You may would like to look also on the juniper forums.

Hope to help


Mohamed Sobair Wed, 07/08/2009 - 07:11


If the BGP in Established state, then the nexthop should be reachable.

Here is the syntax in Juniper:

check with: (Sh route protocols bgp). you should get all Networks advertised by Cisco router UNLESS you have policy dening it at Juniper.

Your config on Cisco router looks fine, make sure you dont have filtering policies at the Juniper J series. Please also post configuration in Juniper if the problem still not rectified.

The BGP Dampening rule has no affect on the current problem, Juniper has different Default dampening parameters than Cisco (default dampening parameters). even if its not configured in Cisco, the Juniper router shall suspend Networks if the penalty points reached 2000 by default.



k.hariharan1 Wed, 07/08/2009 - 21:14

hi mohamed,

in sh route protocol bgp output, my advertised default route is not coming.

k.hariharan1 Wed, 07/08/2009 - 22:21

Juniper6350> show route all

inet.0: 9 destinations, 10 routes (9 active, 0 holddown, 1 hidden)

+ = Active Route, - = Last Active, * = Both *[BGP/170] 01:58:55, localpref 100

AS path: 9583 I

> to 202.x.x.49 via ge-0/0/3.0

[BGP/170] 00:00:57, MED 0, localpref 100, from 61.x.x.157

AS path: 17820 I


k.hariharan1 Wed, 07/08/2009 - 22:34

default route is learned via two peer but the default route learned via my peer is unusable

wat could be the problem?

any clue?


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