BGP world routes with one 2951 and two fiber connections from one provider

Thomas Ossman · ‎05-18-2015

I work for a small ISP that has two fiber connections from Level3, both fibers plug into a single Cisco 2951. The two fibers are both limited to 500 Mbps, currently we are set up to use just one fiber at a time. Our owner would like to change that by having Level3 provide us with BGP world routes so we can leave both fiber interfaces up and let BGP determine which line to use. I have no BGP experience so I am a little lost at the moment on how to do all of this but for the moment I am worried about whether or not one 2951 would be able to handle this. From what I have read already with a Gig of memory the router should be able to handle the routes in it's table. I have two Gigs in this router just for good measure. What I am unclear about is whether or not the router's processor will be able to handle this setup. Any information as to whether or not it can would be greatly appreciated.

Richard Burts · ‎05-18-2015

With two connections, both of them to Level3, I do not see a lot of benefit in running BGP and accepting full Internet routes. With two providers it does make sense. But if you run BGP on both connections what will Level3 advertise differently on one link as compared to the other? I think you would be much better suited to configure dual default routes and let IOS manage load sharing to be able to use both connections.

HTH

Rick

HTH

Rick

Thomas Ossman · ‎05-19-2015

I think my boss wants to do it like that because the two fibers terminate in two different cities and it would give us a Gigabit connection from Level3. But as I read more about BGP I am beginning to realize that he may not really understand how BGP works. Actually as I have been teaching myself BGP I have thought that what you are suggesting is the better way to go. In case I cannot convince him that world routes will not benefit us, is the processor in a 2951 capable of handling it?

Joseph W. Doherty · ‎05-19-2015

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Posting

Regarding your last question about performance, Cisco recommends a 2951 for up to 75 Mbps of WAN (i.e. duplex) bandwidth. Although Cisco's recommendations are conservative, 500 Mbps, or Gig, is a bit much for a 2951.

Thomas Ossman · ‎05-19-2015

I understand that Cisco is conservative with their recommendations but when I do a speed test to speedtest.net from my office I can pull over 300 Mbps up and down. I freely admit that I am in over my head in my current position but how am I getting over 4 times what they say?

Joseph W. Doherty · ‎05-19-2015

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In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

"Your mileage may vary". ;)

See attachment for all the gory details.

Thomas Ossman · ‎05-19-2015

Oddly enough I found that paper right after I posted my last response, but thank you for referring me to it. If you don't mind backtracking with me for a second. I actually just got a chance to talk to my boss and mentioned what Rick had said about world routes from one provider not really benefiting us. I was right that he thinks that with one fiber going East to terminate in the closest city to the East and the other fiber going West to terminate in the closest city to the West that we are "technically" multi-homed. Is that an accurate statement, or is his understanding wrong?

Richard Burts · ‎05-19-2015

Whether you are multi homed or not depends a bit on your frame of reference and perhaps on how you interpret the term. From a physical perspective you certainly can claim to be multi homed. From a routing perspective I would argue that you are not really multi homed. To be really multi homed from a routing perspective you would learn one set of routes at one location and would learn a different set of routes at the other location. So ask your boss what will Level3 advertise differently to the East than it advertises to the West? It seems to me that Level3 has one set of full Internet routes and it will advertise that same set to both locations. And while he can claim "technical" multi homing it will not achieve the results usually associated with multi homed BGP.

HTH

Rick

HTH

Rick

Joseph W. Doherty · ‎05-19-2015

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Rick is correct, you're not multi-homed in the BGP sense. However, often you can arrange to exchange additional information with a provider (via BGP) to more optimally use your multiple links, especially if they are geographically diverse as you describe yours are.

Or, if your IOS is licensed for PfR, it can dynamically load balance and/or pick the optimal link to your various destinations. (It also doesn't need BGP to do this.)

If you wanted to pursue either, you would probably want to retain a network consultant, as both are more advanced than basic BGP.

Thomas Ossman · ‎05-20-2015

Excellent, thank you both for the information. I'll have to ask Level3 if there would be any difference in their routes going East and going West. I appreciate the help.