Solved

BGP Inbound Route Preference

Posted on 2008-10-11
10
864 Views
Last Modified: 2012-05-05
Hello, I am completely new to BGP and was wondering how I can modify routes coming IN from the Internet. I have two carriers providing me each with a class C block of addresses. I'd like to have both blocks coming in through a single carrier which it currently is, but through the wrong carrier. How can I swap it to the second carrier? Thanks!
0
Comment
Question by:MardukLitzer
[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
  • 4
  • 4
  • 2
10 Comments
 
LVL 8

Expert Comment

by:sstone55423
ID: 22694161
Weight Attribute
Weight is a Cisco-defined attribute that is local to a router. The weight attribute is not advertised to neighboring routers. If the router learns about more than one route to the same destination, the route with the highest weight will be preferred. In Figure 39-2, Router A is receiving an advertisement for network 172.16.1.0 from routers B and C. When Router A receives the advertisement from Router B, the associated weight is set to 50. When Router A receives the advertisement from Router C, the associated weight is set to 100. Both paths for network 172.16.1.0 will be in the BGP routing table, with their respective weights. The route with the highest weight will be installed in the IP routing table.
Figure 39-2 BGP Weight Attribute
 
See http://www.cisco.com/en/US/docs/internetworking/technology/handbook/bgp.html#wp1020576
 
0
 
LVL 2

Author Comment

by:MardukLitzer
ID: 22694203
so both of my routers show weight 0 for the route in question... Should I set it higher on the one where I'd like it to come in?
0
 
LVL 8

Expert Comment

by:sstone55423
ID: 22694315
" the route with the highest weight will be preferred. " So, yes.
 
One thing I noted is that your question said "I'd like to have both blocks coming in through a single carrier which it currently is"  I am not sure I get that.  Isn;t one block coming in through one carrier, and the other block from the other carrier?
0
Easy, flexible multimedia distribution & control

Coming soon!  Ideal for large-scale A/V applications, ATEN's VM3200 Modular Matrix Switch is an all-in-one solution that simplifies video wall integration. Easily customize display layouts to see what you want, how you want it in 4k.

 
LVL 43

Accepted Solution

by:
JFrederick29 earned 500 total points
ID: 22694798
Weight will only affect outbound routing.  If you want inbound traffic to prefer one ISP over the other, you can prepend your as-path a few times when advertising routes to the less preferred ISP.  This makes the primary ISP the more preferred path.  See the following for an example and explanation:

http://blog.ioshints.info/2008/02/bgp-essentials-as-path-prepending.html
0
 
LVL 2

Author Comment

by:MardukLitzer
ID: 22704098
I will be giving this a shot tonight... Another question I have is, can I set the iBGP to send traffic originating from a class C through a particular router and the other class C through the second router?
0
 
LVL 43

Expert Comment

by:JFrederick29
ID: 22704215
You mean outbound traffic from yourself to the Internet, right?

Without knowing anything about your topology...

One way you can control this is via HSRP on your BGP routers.  You can make one router the active HSRP router for the subnet that you want routed out one ISP and the other router the HSRP active router for the other subnet.  If this method of control isn't a viable option, Policy Based Routing could be used on the hop prior to your BGP routers.
0
 
LVL 2

Author Comment

by:MardukLitzer
ID: 22704266
Ok, I have a default route to one of the gateways and from there it goes out over our DS3 link, or if that is down it goes out over our other circuit...So currently the iBGP will always go out over the DS3 unless there is a failure... What could I change with it to sort of do a selection process based on source network?
0
 
LVL 43

Expert Comment

by:JFrederick29
ID: 22704309
What device has the default route to your BGP router?  Is it capable of policy routing?  Policy routing (PBR) in Cisco speak allows you to route based on source.  Are you only receiving a default route from your ISP's?  Do you have local preference for the default setup?
0
 
LVL 2

Author Comment

by:MardukLitzer
ID: 22704351
My ASA has the default route, running 7.2(4). I am not sure if it is capable of policy routing. I am receiving only default routes, and currently I have local preferences set up (as of tonight if it works)...
0
 
LVL 43

Expert Comment

by:JFrederick29
ID: 22704467
Yeah, the ASA doesn't do policy routing and local preference influences routes learned from your ISP (default in this case) so that won't help with your source routing dilemma.  You can use PBR on your edge BGP routers (assuming Cisco something) but you lose the dynamic element of routing via BGP.
0

Featured Post

[Webinar] Code, Load, and Grow

Managing multiple websites, servers, applications, and security on a daily basis? Join us for a webinar on May 25th to learn how to simplify administration and management of virtual hosts for IT admins, create a secure environment, and deploy code more effectively and frequently.

Question has a verified solution.

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

Problem Description:   Couple of months ago we upgraded the ADSL line at our branch office from Home to Business line. The purpose of transforming the service to have static public IP’s. We were in need for public IP’s to publish our web resour…
Tired of waiting for your show or movie to load?  Are buffering issues a constant problem with your internet connection?  Check this article out to see if these simple adjustments are the solution for you.
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…

734 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