OpenBGPd: AS path prepend for certain networks only?

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OpenBGPd: AS path prepend for certain networks only?

bernd-34
Hi,

running OpenBSD 5.3 (amd64) for BGP routing for more than one and a half
years without any trouble -- thanks guys!

However, as setups evolve, new questions may arise. As far as I get from
the man pages, it's only possible 'globally' to apply prepending to AS
paths:

      prepend-neighbor number
              Prepend the neighbor's AS number times to the AS path.

      prepend-self number
              Prepend the local AS number times to the AS path.

I'd like to do this only for certain networks in our AS, to force
ingress and egress traffic over a certain uplink -- leaving all other
networks untouched by this.

Is that possible with OpenBGPd?

Thanks,

Bernd

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Re: OpenBGPd: AS path prepend for certain networks only?

Gregory Edigarov-5
On 06/13/2013 11:36 AM, Bernd wrote:

> Hi,
>
> running OpenBSD 5.3 (amd64) for BGP routing for more than one and a half years without any trouble -- thanks guys!
>
> However, as setups evolve, new questions may arise. As far as I get from the man pages, it's only possible 'globally' to apply prepending to AS paths:
>
>       prepend-neighbor number
>               Prepend the neighbor's AS number times to the AS path.
>
>       prepend-self number
>               Prepend the local AS number times to the AS path.
>
> I'd like to do this only for certain networks in our AS, to force ingress and egress traffic over a certain uplink -- leaving all other networks untouched by this.
>
> Is that possible with OpenBGPd?

something like
  match to your_neighbor_here prefix 192.168.2.0/24 set prepend-self 2
  match from your_neighbor_here some.other.prefix.0/NN set prepend-neighbor 3


--
With best regards,
      Gregory Edigarov

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Re: OpenBGPd: AS path prepend for certain networks only?

Stuart Henderson
On 2013-06-13, Gregory Edigarov <[hidden email]> wrote:

> On 06/13/2013 11:36 AM, Bernd wrote:
>> Hi,
>>
>> running OpenBSD 5.3 (amd64) for BGP routing for more than one and a half years without any trouble -- thanks guys!
>>
>> However, as setups evolve, new questions may arise. As far as I get from the man pages, it's only possible 'globally' to apply prepending to AS paths:
>>
>>       prepend-neighbor number
>>               Prepend the neighbor's AS number times to the AS path.
>>
>>       prepend-self number
>>               Prepend the local AS number times to the AS path.
>>
>> I'd like to do this only for certain networks in our AS, to force ingress and egress traffic over a certain uplink -- leaving all other networks untouched by this.
>>
>> Is that possible with OpenBGPd?
>
> something like
>   match to your_neighbor_here prefix 192.168.2.0/24 set prepend-self 2
>   match from your_neighbor_here some.other.prefix.0/NN set prepend-neighbor 3
>
>

For ingress traffic: You can *influence* things in this way, but if you
want to *force* ingress traffic for a certain prefix to always come in
over a certain link, you cannot advertise it out of other uplinks at
all - if somebody sets a higher localpref for you on their network then
it doesn't matter how long the AS path is, the localpref always trumps
this.

For egress traffic (I am understanding this as "I want traffic generated
by certain prefixes on my network to always be sent via a certain
transit provider" or similar): this can't be done with BGP, or indeed
by the routing table at all, you would need to PF route-to rules or
similar.