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BGP Route Selection for Single Prefix

How can I manipulate incoming traffic from a specific prefix from my ISP to come through my other ISP to elevate the traffic on my 1 peer router?

I have the following setup:

ISP-A                              ISP-B

   |                                       |

eBGP                              eBGP

   |                                       |

Rtr-A                                Rtr-B

     |---------iBGP-------------------|

I noticed that traffic for a prefix from ISP-A 206.160.170.0/16 (streaming) is congesting my WAN interface on Rtr-A. I would like to be able to push the traffic "INBOUND" from 206.160.170./16 through ISP-B/RTR-B. I know that I can manipulate the "localpref" to do the outbound traffic, but want to do this for only this prefix, which this prefix is part of ISP-A AS.

Any suggestions?

Everyone's tags (2)
7 REPLIES

BGP Route Selection for Single Prefix

Not possible. Routing is destination based. If you want to manipulate inbound traffic then you can only manipulate traffic TO local prefix, not traffic FROM foreign prefix.

New Member

Re: BGP Route Selection for Single Prefix

enable net flow and determine which /24s of the /16 are causing highest utilization and then you should be able to receive those on different routers by using AS path using community in a routing policy that can essentially load balance your traffic.

Sent from Cisco Technical Support iPhone App

New Member

BGP Route Selection for Single Prefix

Can you please provide a possible example with the communities? I provided further information on the bottom or below this thread.

Would this work? This would affect "OUTBOUND" and not INBOUND - Though

route-map as30263_in permit 5

match ip address prefer_as30263

set local-preference 250

!

ip access-list standard prefer_as30263

permit 96.0.0.0 0.255.255.255

permit 74.0.0.0 0.255.255.255

New Member

Re: BGP Route Selection for Single Prefix

Hi,

There are a few ways to solve this problem. With out knowing a bit more about your configuration i'll just throw out a few ideas.

1) you can use conditional advertisements, remove the prefix in question from ISB-A and advertise it through ISP-B. With conditional advertisements you still maintain failover capabilities as the prefix will be advertised through the other ISP in the event of a failure if configured correctly.

2) AS prepending, append the AS a few times to make the inbound routes less desirable through ISP-A.

If you need any more help just ask.

Thanks,

Jesse

Re: BGP Route Selection for Single Prefix

Guys, he was asking:

"I would like to be able to push the traffic "INBOUND" from 206.160.170./16 through ISP-B/RTR-B"

Neither of the above solutions achieve this. Your solutions are for controlling inbound traffic to the local prefixes, and not from foreign prefixes.

New Member

Re: BGP Route Selection for Single Prefix

Here is some more details:

The supernet 206.160.170.0/16 is owned and advertised by AS 1239

ROUTER1#show ip ro 206.160.170.0
Routing entry for 206.160.0.0/16, supernet
  Known via "bgp 65001", distance 20, metric 0
  Tag 1239, type external
  Last update from xxx.xxx.xx.77 7w0d ago
  Routing Descriptor Blocks:
  * xxx.xxx.xx.77, from xxx.xxx.xx.77, 7w0d ago
      Route metric is 0, traffic share count is 1
      AS Hops 1
      Route tag 1239


ROUTER1#show ip bgp 206.160.170.0
BGP routing table entry for 206.160.0.0/16, version 20423274
Paths: (1 available, best #1, table Default-IP-Routing-Table)
  Advertised to update-groups:
        1
  1239
    xxx.xxx.xx.77 from xxx.xxx.xx.77 (xxx.xxx.xxx.121)
      Origin IGP, metric 0, localpref 200, valid, external, best
      Community: 81199227 81200104 81200107

-As at this time I have the localpref set for 200 for the routes received from AS 1239 at this time on Router 1 and localpref set for 150 for the routes received from AS 30263 on Router 2.

As noted from Router 2 the following output for 206.160.170.0:

ROUTER2#show ip ro 206.160.170.0

Routing entry for 206.160.0.0/16, supernet

  Known via "bgp 65001", distance 200, metric 0

  Tag 1239, type internal

  Last update from xxx.xxx.xx.77 3w0d ago

  Routing Descriptor Blocks:

  * xxx.xxx.xx.77, from 10.255.1.1, 3w0d ago

      Route metric is 0, traffic share count is 1

      AS Hops 1

      Route tag 1239

ROUTER2#show ip bgp 206.160.170.0

BGP routing table entry for 206.160.0.0/16, version 116873587

Paths: (3 available, best #1, table Default-IP-Routing-Table)

  Not advertised to any peer

  1239

    xxx.xxx.xx.77 (metric 19200) from 10.255.1.1 (10.1.10.11)

      Origin IGP, metric 0, localpref 200, valid, internal, best

  30263 30263 30263 30263 30263 30263 30263 30263 30263 30263 30263 209 1239

    xxx.x.xxx.137 from xxx.x.xxx.137 (xxx.x.xxx.117)

      Origin IGP, localpref 150, valid, external

  30263 30263 30263 30263 30263 30263 30263 30263 30263 30263 30263 209 1239, (received-only)

    xxx.x.xxx.137 from xxx.x.xxx.137 (xxx.x.xxx.117)

      Origin IGP, localpref 100, valid, external

--  The issue is that the traffic from this particular prefix is high BW and I would like to move it through Router 2

- I understand if I change the local pref then this will change the direction of going out through Rtr 1 - By adding an additional line to the Route-map and filtering it to the specific prefix correct to set the pref lower through Rtr 1

-But In order to make the "incoming" prefer Router 2 - just for that 1 prefix 206.160.170.0/16 is not possible?

Thank you for your time and responses.

BGP Route Selection for Single Prefix

I'll put it simple:

changing local preference on incoming advertisements of foreign prefixes controls outbound traffic path to those foreign networks

prepending AS-PATH on outgoing advertisements of local prefixes controls inbound traffic path to your local networks

You are trying to control inbound traffic path FROM the foreign networks. This is not possible.

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