If you are using Cisco... http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6554/ps6599/ps8787/product_data_sheet0900aecd806c4ee4.html
On Wed, Dec 30, 2009 at 12:38 PM, Dylan Ebner <[email protected]>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 > [email protected] > www.consultingradiologists.com > > > -----Original Message----- > From: Simon Chen [mailto:[email protected]] > Sent: Wednesday, December 30, 2009 11:03 AM > To: [email protected] > 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
