3 T1's 1 router with BGP

[mialbert]

We currently have 1 T1 with one provider but are going to be going to 3 T1's and 3 providers. We will be running 2 T1's simultaneously at sporadic times during the weekends. I am wondering if i can guarantee failover to the 3rd unused T1 with BGP, should there be an outage. Thank You

[suttonr]

Hey,

I guess the first question is, are these going to serial intf's only or? You can configure your primary serial link to fail over to your seconday interface using "backup interface" commands, but you must determine your Primary/Secondary and which link will be your backup out of the three. But, you must specify on the Serial Intf config about your backup command statements.

IE:

interface serial 0

backup interface serial 1

etc....

You can also use restore timers (To automatically switch traffic back to the original path) so that if and when your primary link comes back up it will resume passing traffic on its original intf and the backup link will no longer be utilized for traffic at that point.

[vcjones]

First, an answer: You can pretty much do whatever you want with BGP, but some things are more difficult than others. The environment you describe sounds very casual and not altogether consistent. You just normally don't take multiple T1's to multiple ISPs and randomly turn them on and off. Are you sure we are talking about T1 lines here? What kind of connections you have can make a significant difference.

Beyond that, how you are using the Internet is critical to how you provide failover. If you are hosting a server accessed from the Internet, BGP is your only good choice unless the only server you are hosting is an email server or you have some degree of control over the client software.

There is a brief white paper on my web site which reviews some of the many techniques which can be used to support multihoming an Internet connection. You might find it interesting reading.

Good luck and have fun!

Vincent C Jones

www.networkingunlimited.com

[NPT_2]

Is there a particular reason why you would like to use the 2 T1's at one given time over the 3rd? If you setup bgp and keep all 3 T1's active at one time traffic should take the quickest path inbound and outbound, you could really lose any 2 of the 3 T1's and the traffic should transparently reroute with minimal if any noticable outage. If you prefer to have most of your traffic go over the 2 T1's set up prepending to provide preference to the 2 T1's over the 3rd, but still have redundancy with the third. We are doing this with a DS3 and 2 T1's and it works great.

[NPT_2]

A link you might also find useful on this:

http://www.cisco.com/en/US/tech/tk365/tk80/technologies_configuration_example09186a00800945bf.shtml