If you are using Cisco... http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6554/ps6599/ps8... On Wed, Dec 30, 2009 at 12:38 PM, Dylan Ebner <dylan.ebner@crlmed.com>wrote:
Simon- We do exactly what you are trying to accomplish. We have two routers and two providers. Provider A is our primary and we receive partial routes from them (no static route). Then Router B is connected to Provider B with no default route (basically it looks like we are not advertising to them). Our AS on router b is prepended several times. Router A and B are connected via iBGP to eachother. Then, using interface tracking (we are a cisco shop) we can fail to provider B. So, about the only failure we cannot automatically recover from is if we have our router A interface / layer1 to provider A start to fail and we get enough traffic through to keep BGP up, but errors make ip traffic fail.
This failover has worked server times while in production. Mostly we see our BGP drop from provider A, but we have also seen link down from provider a. In testing we failed links and routers, which always recovered just fine. But we all know the lab can be completely different from the real world.
If you want to see how this work for us, go to bgplay.com and enter the following:
Network: 67.135.55.0/24
Start: 26/12/2009 20:00:00 End: 27/12/2009 07:00:00
Pull out 19629 (ME) 209 (Qwest, provider A) 7263 (GoFast. Dba Sungard, provider B)
At about 20:11 you see the routes start failing to AS7263 and then at about 6:23 the next day they start failing back.
This example happened when Qwest lost an edge router in Minnesota. Link status was up, but BGP tables were lost, so we had no router out to qwest.
Dylan Ebner, Network Engineer Consulting Radiologists, Ltd. 1221 Nicollet Mall, Minneapolis, MN 55403 ph. 612.573.2236 fax. 612.573.2250 dylan.ebner@crlmed.com www.consultingradiologists.com
-----Original Message----- From: Simon Chen [mailto:simonchennj@gmail.com] Sent: Wednesday, December 30, 2009 11:03 AM To: nanog@nanog.org Subject: question regarding multi-homing
Hi all,
Happy new year...
I have a question regarding multi-homing, mostly from stub network's operational point of view. My big question is: what kind of failures do you usually see from your providers? Link down? Link up, but withdraw some routes? Link up, no route change, but blackholing partial or all traffic? Anything else?
Let's say that I have two local routers (Ra and Rb) connecting to two providers, A and B. If router Ra sees provider A with problems of the first two cases (link down, link up but withdraw routes), the Rb can easily step up. My question is, if I am using provider A as the default, but provider A has the third problem (link up, no route change, but blackholing traffic), how can I detect it and switch provider automatically?
To state this problem in detail: I use a static default route on Ra to forward traffic to provider A, or receive 0/0 from provider A via BGP. For some reason, provider A can no longer reach a /24. My network cannot be notified (unless, I receive a full internet routing table). In this case, all I know is that my traffic to /24 is blackholed through provider A. In this case, is there an automatic way for my stub network to switch over to provider B? Do I have to do the detection and switch over manually? I don't think VRRP can help here, right?
Thanks. -Simon
-- To him who is able to keep you from falling and to present you before his glorious presence without fault and with great joy