BGP Attributes Setting

[Ahmed Erfan Mehdi]

Hello Expert,

I have three links with three ISPs, each link connect separately to ISPs .... so i used weight and local preference as bgp attributes .... at first i was using three links on service with same attributes for all of them .. then i tried to use two links on service and then i tried to use one link on service ... the problem  is , nowadays i am facing many flaps from the providers side, so what is the advised solution for this issue ?

it is highly appreciated for any help offer.

Regrds,

Ahmed   

[cadet alain]

Hi,

Can you explain what you mean by many flaps from isps ?

Regards.

Alain

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[Ahmed Erfan Mehdi]

Dear Cadet,

my IGW router is connected to 3 ISPs through three links, sometimes i face a flap ( short outage ) from one of the ISPs and based on bgp attributes my router will choose another ISP and so on. this flap is causing a short outage to my service, would you please advice me how can i control that ? let me if the case is not clear to you .. thanks in advance for your help.

Regards,

Ahmed

[cadet alain]

so you don't want a flapping from interface between you and this ISP to change the BGP path selection and choose another BGP path?

are you directly connected with your ISP( i mean not between loopbacks) ? if so then if you disable bgp fast-external fall-over, you'll have to wait for the tcp holddown which is 180 sec by default before the BGP peering is down.

so BGP will not choose another ISP but your traffic will be black-holed, is this what you really want ?

Regards.

Alain

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[Ahmed Erfan Mehdi]

Hello Cadet,

Thanks to reply ... my aim is, when the is a short outage or flapping from one of my ISPs then my router will choose another ISP, it is by nature so during this operation i dont want to be affected to my service not even the customers know that there is a short outage ....

onething else, some time my STM16 is fully utilized so i will get drop on the service,  in this case i used to move some prefixes to othe link to decrease the load ...

those are my aims .. so how you can help me in that.... thanking you

Regards,

Ahmed

[MUKUL JOSHI]

Hi Ahmed,

You can load balance between all three links ...but keep in mind that all attributes should be same including the as-path.

If that is the case then if one link goes down your traffic will be shifted to second one and so on.....

If that is what you want then kindly reply.

HTH

MJ

[cadet alain]

Hi,

yes i didn't think about multipath  :

router bgp xxx

maximum-paths xxx

http://blog.alwaysthenetwork.com/tutorials/bgp-multipath-relax/

Regards.

Alain

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[Ahmed Erfan Mehdi]

Hi Mukul,

thanks for sharing idea.

let me clarify it based on your idea, at routing table ( IP CEF ) i will have three routes, once the 1st one is down so i will use the 2nd by nature but the things that used to happen when the first link comes back on service hte 2nd link ( BGP session ) will reset and that cause a high cpu usage, at result the customer got short outage ....

let me know how things are ...

Dear Cadet, what do you think ?

Regards,

Ahmed