[c-nsp] Inbound traffic

Sherwin Torres kuscent01 at yahoo.com.ph
Wed Feb 10 00:28:46 EST 2010

Hi Jon & Aftab,

Thank you very much for your inputs.

Anyway, I agree but you might confuse on my inquiry. In the internet cloud, there are lots of interconnected AS and if I'm going to prepend the announcement to AS200 and AS300 - all inbound traffic will pass to AS20 alone. 

Actually, what I want is - to isolate specific AS (AS1) to pass via AS400-AS20-AS30 as the primary returned path while other AS from the internet cloud would be still the best path going to AS30. 


--- On Wed, 2/10/10, Aftab Siddiqui <aftab.siddiqui at gmail.com> wrote:

From: Aftab Siddiqui <aftab.siddiqui at gmail.com>
Subject: Re: [c-nsp] Inbound traffic
To: "Jon Lewis" <jlewis at lewis.org>
Cc: "Sherwin Torres" <kuscent01 at yahoo.com.ph>, cisco-nsp at puck.nether.net
Date: Wednesday, 10 February, 2010, 1:05 PM

Hi Sherwin,
Inbound traffic can also be altered on the basis of prefix-advertisement. If you are advertising more specific prefix i.e. /22 or /24 (though not recommended with tier1 service providers) your inbound traffic will always take the desired path.

and yes as-path prepend is also an option.


Aftab A. Siddiqui

On Wed, Feb 10, 2010 at 8:23 AM, Jon Lewis <jlewis at lewis.org> wrote:

On Wed, 10 Feb 2010, Sherwin Torres wrote:

1. AS1 - AS200 - AS30
2. AS1 - AS300 - AS30
3. AS1 - AS400 - AS20 - AS30

In the above scenario, I am using AS30 and I need to access AS1. The

outbound traffic can be force using the localpref to prefer which
path I can use for the outbound however, my dilemma is the inbound
traffic. Since sample 1 and 2 has lesser path from AS1 going to AS30,
this might be the best in returned path while sample 3 is the least

priority due to longer path. Is there a way can I manipulate the inbound and outbound via sample 3 without contacting AS1?

The short answer is as-path prepending of your announced routes to as200 and as300.

 Jon Lewis                   |  I route
 Senior Network Engineer     |  therefore you are
 Atlantic Net                |

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