Solved

bgp AS prepend or local-preference

Posted on 2011-09-16
5
420 Views
Last Modified: 2012-05-12
is there any advantage to using AS prepend over modifying local-preference.  Why would one use one over the other?  I have been using local-preference for incoming bgp routes and wondering if it's worth looking into AS prepend method.

thanks
0
Comment
Question by:FREDARCE
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 3
  • 2
5 Comments
 
LVL 32

Accepted Solution

by:
harbor235 earned 500 total points
ID: 36554259


AS prepend is used to influence how "your routes" appear on the outside of your AS, hence they effect how traffic flows "TOWARDS" your AS.

Local pref is set on incoming routes received from EBGP neighbors typically, thus local pref effects traffic flow towards external ASs.

The difference is the effects on the direction of the traffic flow, one is inbound the other is outbound,
understand?

harbor235 ;|
0
 

Author Comment

by:FREDARCE
ID: 36556608
Ok.  but isn't the result the same?  What I don't understand is why you would use one method over the other?

thanks
0
 
LVL 32

Expert Comment

by:harbor235
ID: 36559419

Traffic is bidirectional, BGP allows you to control both directions, in and out of your AS.
One effects inbound the other effects outbound, the result is control over both directions of your traffic flow. changing only one of the two only effects one direction of your traffic flow.


harbor235 ;}
0
 

Author Comment

by:FREDARCE
ID: 36569577
Ok.  but can't you use LP and apply it to both in and out?

example

   neighbor x.x.x.x route-map LP500 ?

in Apply map to incoming routes
out Apply map to outbound routes
0
 
LVL 32

Expert Comment

by:harbor235
ID: 36570124


local pref and MEDs (outbound metric) are two seperate BGP route attributes and are treated separately
when received by a BGP speaker. So the answer is no you cannot set LP inbound and outbound.

you set LP in a route map like this:

set local-pref 200

you set outbound MEDs like this:

set metric 200


harbor235 ;}
0

Featured Post

Get MySQL database support online, now!

At Percona’s web store you can order your MySQL database support needs in minutes. No hassles, no fuss, just pick and click. Pay online with a credit card.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Auditors face some challenges when reviewing router and firewall configurations.  I'm going to discuss a few of them in this article.  My assumption is that there is a device hardening standard in place, which points out the key elements of configur…
Creating an OSPF network that automatically (dynamically) reroutes network traffic over other connections to prevent network downtime.
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…

623 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question