Thanks to Howard and John. I'm definitely Howard's fans of his BGP paper . My thinking to your suggestion is: 1. The easiest method is to ask ISP to announce default information to us and then we apply route-map to set local_pref (in fact, I don't know how to do it because neighbor route-map has no effect on incoming updates when matching based on IP address; so I wonder Halabi's example on p.379 is wrong). But using static default route is more preferable because we have more control over the routing behaviour. Also it has the troublesome of asking the ISP to change configuration. 2. Then in my example, I set a default route in A pointing to C and a default route in B pointing to D. Remember my purpose is to prefer the A-C path. Then problem comes. I was thinking of redistributing static route into BGP (by default-originate, etc) and then advetise this default route between A and B (by neighbor default-originate route-map). Then I thought setting local_pref on A and B will achieve my purpose. However, since I have set the default route statically, this route has ad=1 and will thus always appear in the ip route table. This means all hosts behind A will use A's default route to go to internet, and all hosts behind B will use B's default route to go to internet. This is fine but not my objective. 3. Therefore, I think I CANNOT achieve my objective using static default route which points to ISP's router interface. Rather I think the more efficient method is to use HSRP between router A and B. A is active and B is standby. Both A and B have their static default route pointing to their own ISP. The static route is NOT redistributed into BGP. Then I can achieve my target : A as primary default gateway and B as backup. But what about if A and B are far away connected by WAN link ? HSRP can't run in this situation. I have no solution. My solution suggests BGP has NO ways to achieve the "Primary/Backup default route infrastructure using static IP address of the next hop gateway". Thus Halabi doesn't show such an example. Howard doesn't either. The above are all my personal thinkings. You are all welcome to comment and correct me if you disagree. Let's discuss and learn. Thank you. Cheers, YY -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Howard C. Berkowitz Sent: Sunday, March 25, 2001 9:07 AM To: [EMAIL PROTECTED] Subject: Re: Question on Halabi's BGP default route example >Hi, > >I face this problem when reading Halabi's classic (p.377-382). I >also face such a problem in my supported network. > >Router A and B run iBGP in AS1. A runs eBGP with C in AS2. B runs >eBGP with D in AS3. >I want the A-C path be the primary default and the B-D path be the >backup default. >(Note this is not exactly the same as Halabi's example) > >In Halabi's example, he uses a default route pointing to a network >(e.g. ip route 0.0.0.0 0.0.0.0 193.78.0.0). Then he uses route-map >to set different local_preference based on matching the subnet ip. >The point is this subnet must be advertised inbound from the ISP so >that we can apply inbound route-map. > > But my problem is that in reality we usually use static default >route pointing to the ISP's router interface (e.g. ip route 0.0.0.0 >0.0.0.0 193.78.1.1). This route is statically entered but not >learnt dynamically. Then how can I set local_pref to this default >route ? How can I advertise this route message to the iBGP peer ? >I have thought of redistributing static route but it doesn't really >make sense and seems too complex. Why doesn't it make sense? You are saying you want to advertise something. Static routes don't advertise. The only ways to get a static route into a routing protocol is to hear it from another speaker of the same protocol, or to redistribute it. Other speakers can advertise either because they learned it, redistributed it, or use default information originate. > >I believe you may also have experienced such a setup. What's the >more practical solution ? Thank you in advance. > >Cheers, >YY _________________________________ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _________________________________ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
