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BGP Traffic Engineering question

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drew.weaver at thenap

Nov 10, 2009, 10:31 AM

Post #1 of 5 (516 views)
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BGP Traffic Engineering question

Howdy,

If you have several transit providers connected to your network and much of your traffic is generally directed by the "BGP tiebreaker" (i.e. lowest IP address) is there a way, without specifying on a per-prefix basis to prefer the "tie breaker winner" slightly less often? I don't want to "completely flip" the preference so that it just saturates a different link, I am just trying to see if there is any good way to influence the "natural" selection method.

We have 6 transit providers, and Level3 always wins because it is 4/8, normally this isn't a problem because we have traffic engineering systems (route science/avaya) which move traffic away from that link, but if we need to reboot the RS, or something catastrophic happens we would like it to spread out a little more evenly.

Anyone have any thoughts on this?

-Drew

jeffrey.lyon at blacklotus

Nov 10, 2009, 10:33 AM

Post #2 of 5 (485 views)
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Re: BGP Traffic Engineering question [In reply to]

Isn't Route Science EOL?

Jeff

On Tue, Nov 10, 2009 at 1:31 PM, Drew Weaver <drew.weaver [at] thenap> wrote:
> Howdy,
>
> If you have several transit providers connected to your network and much of your traffic is generally directed by the "BGP tiebreaker" (i.e. lowest IP address) is there a way, without specifying on a per-prefix basis to prefer the "tie breaker winner" slightly less often? I don't want to "completely flip" the preference so that it just saturates a different link, I am just trying to see if there is any good way to influence the "natural" selection method.
>
> We have 6 transit providers, and Level3 always wins because it is 4/8, normally this isn't a problem because we have traffic engineering systems (route science/avaya) which move traffic away from that link, but if we need to reboot the RS, or something catastrophic happens we would like it to spread out a little more evenly.
>
> Anyone have any thoughts on this?
>
> -Drew
>
>
>

--
Jeffrey Lyon, Leadership Team
jeffrey.lyon [at] blacklotus | http://www.blacklotus.net
Black Lotus Communications of The IRC Company, Inc.

Platinum sponsor of HostingCon 2010. Come to Austin, TX on July 19 -
21 to find out how to "protect your booty."

drew.weaver at thenap

Nov 10, 2009, 10:36 AM

Post #3 of 5 (489 views)
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RE: BGP Traffic Engineering question [In reply to]

Sure, it still works however (for now).

-Drew

-----Original Message-----
From: jeffrey.lyon [at] gmail [mailto:jeffrey.lyon [at] gmail] On Behalf Of Jeffrey Lyon
Sent: Tuesday, November 10, 2009 1:34 PM
To: Drew Weaver
Cc: nanog [at] nanog
Subject: Re: BGP Traffic Engineering question

Isn't Route Science EOL?

Jeff

On Tue, Nov 10, 2009 at 1:31 PM, Drew Weaver <drew.weaver [at] thenap> wrote:
> Howdy,
>
> If you have several transit providers connected to your network and much of your traffic is generally directed by the "BGP tiebreaker" (i.e. lowest IP address) is there a way, without specifying on a per-prefix basis to prefer the "tie breaker winner" slightly less often? I don't want to "completely flip" the preference so that it just saturates a different link, I am just trying to see if there is any good way to influence the "natural" selection method.
>
> We have 6 transit providers, and Level3 always wins because it is 4/8, normally this isn't a problem because we have traffic engineering systems (route science/avaya) which move traffic away from that link, but if we need to reboot the RS, or something catastrophic happens we would like it to spread out a little more evenly.
>
> Anyone have any thoughts on this?
>
> -Drew
>
>
>

--
Jeffrey Lyon, Leadership Team
jeffrey.lyon [at] blacklotus | http://www.blacklotus.net
Black Lotus Communications of The IRC Company, Inc.

Platinum sponsor of HostingCon 2010. Come to Austin, TX on July 19 -
21 to find out how to "protect your booty."

lists at die

Nov 10, 2009, 12:04 PM

Post #4 of 5 (487 views)
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Re: BGP Traffic Engineering question [In reply to]

On Tue, 10 Nov 2009, Drew Weaver wrote:

> If you have several transit providers connected to your network and much
> of your traffic is generally directed by the "BGP tiebreaker" (i.e. lowest
> IP address) is there a way, without specifying on a per-prefix basis to
> prefer the "tie breaker winner" slightly less often?

Assuming Cisco, set "bgp always-compare-med", "bgp deterministic-med", and
in your route-map in, "set origin igp" and "set metric X". You can then
vary X as you see fit as an alternate tie-breaker. As long as you never set
the metric the same on two different paths for the same prefix, it'll never
fall back to router-id.

Depending on the transit provider, you can often match bgp communities to
determine which are customer routes or the region where the announcement was
heard, which you can then use as a tie-breaker when setting the metric.
Barring that, as-path access-lists matching specific path fragments can do
the same thing, but seems to take more work to maintain as relationships
change over time.

-- Aaron

jmaimon at ttec

Nov 10, 2009, 12:46 PM

Post #5 of 5 (478 views)
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Re: BGP Traffic Engineering question [In reply to]

Aaron Hopkins wrote:
> On Tue, 10 Nov 2009, Drew Weaver wrote:
>
>> If you have several transit providers connected to your network and much
>> of your traffic is generally directed by the "BGP tiebreaker" (i.e.
>> lowest
>> IP address) is there a way, without specifying on a per-prefix basis to
>> prefer the "tie breaker winner" slightly less often?
>
> Assuming Cisco, set "bgp always-compare-med", "bgp deterministic-med", and
> in your route-map in, "set origin igp" and "set metric X". You can then
> vary X as you see fit as an alternate tie-breaker. As long as you never set
> the metric the same on two different paths for the same prefix, it'll never
> fall back to router-id.
>
> Depending on the transit provider, you can often match bgp communities to
> determine which are customer routes or the region where the announcement
> was
> heard, which you can then use as a tie-breaker when setting the metric.
> Barring that, as-path access-lists matching specific path fragments can do
> the same thing, but seems to take more work to maintain as relationships
> change over time.
>
> -- Aaron
>

Tutorial: Effective BGP Load Balancing Using "The Metric System"
Dani Roisman, Peak Web Consulting

http://tinyurl.com/yzlmmo8

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