2 ISP on one router with BGP

Hi all,

I hate to sound like a noob but I am trying to configure one Cisco 1760 to route traffic to the internet via 2 ISPs.

The router currently has 2 T1's with one being to ATT and the other being to Sprint. From reading through Cisco's site on how to do this everything seems to point to BGP. Is this what I need?

If so what do I need to ask my ISP for to make bgp work?

Also, if one ISP fails or its bandwidth is maxed out can BGP automatically use the other line?


Jarrod Lash

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Hi Jarrod,

You may wish to investigate Cisco's Sample Configuration for BGP with Two Different Service Providers ( Multihoming ):

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Cisco Multihoming White Paper:

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Cisco's Border Gateway Protocol ( BGP ) Links:

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Additionally, you may have interest in Cisco's Primary and Backup WAN Links Using Cisco Optimized Edge Routing.

There are two types of links: primary and backup. The desired behavior for the links is listed below:

· Traffic will move to a secondary link only if all the primary links meet one of the following conditions:

-The link is unavailable

-Routes are not reachable

-Utilization is above the threshold

· Traffic will move back from a secondary link if the primary links have enough head room to accommodate traffic and the prefixes are reachable · Prefixes that are unreachable on a link (primary or secondary) will be moved to a reachable link (primary or secondary)

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Cisco IOS Optimized Edge Routing:

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Hope this helps,

Brad Reese BradReese.Com Cisco Repair Service Experts

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Hendersonville Road, Suite 17 Asheville, North Carolina USA 28803 USA/Canada Toll Free: 877-549-2680 International: 828-277-7272 United Kingdom: 44-20-70784294

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On 20.08.2005 01:55 snipped-for-privacy@gmail.com wrote

your C1760 can take 128 MB DRAM at maximum. Depending on your other applications that might be not enough memory to hold to full BGP tables.

yes. BGP is what you need

Just ask them to run BGP to you.

Usually you will have both lines in production. Unlike e,g. OSPF, BGP is a reachability protocol only. And forget about dynamic loadsharing. You can't do that with BGP.

Have a look at

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as starter for BGP


Reply to
Arnold Nipper

You have a wide range of options available to you. Depending on the applications you are trying to support, you may or may not need to run BGP. See the white paper on my web site "Multi-Homing--Connecting to Two ISPs" for a brief summary of your options and some of the trade offs involved.

Maybe, maybe not. If all you want is to keep browsing despite ISP failure or keep your mail server on line, you don't need BGP. If you are running a web server and you want users to recover from ISP failure in minutes, you need BGP. If you're running a web service and you can't even afford minutes of down time, you need more than just BGP.

You need an Autonomous System Number and a range of IP addresses from one of your ISPs that both ISPs are willing to advertise to the Internet at large. Last time I looked, both ATT and Sprint had web pages describing their requirements for participating in a multihoming BGP setup.

Yes on failure, no on bandwidth. BGP is lousy for load sharing, you're doing great if you get one link within 50% of the other.

Don't forget to also configure your router with defensive access lists. There be dragons out there. See Chapter 8 of my book for more on ISP connectivity (details and sample configurations on my web site) and remember,

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is your friend. You will not succeed unless you learn it well.

Good luck and have fun!

Reply to
Vincent C Jones

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