>One thing to remember is that OSPF costs are calculated >unidirectionally. For example, A's cost to C could be very different from >C's cost to A. In general, IP traffic has to be engineered in both >directions and it for some networks asymmetry in flow might make sense. I >can't think of a reason off hand while watching a hockey game, but >experience has taught me that many odd looking designs are rooted in >rational, informed theory. > >Pete
There's a whole class of applications for this sort of thing, and indeed there is a Unidirectional Link Routing group in the IETF for dealing with them. Much of the leading research work is in France, where practical applications deal with using high-bandwidth satellite links in one direction to deliver educational content to Africa, and a low-speed terrestrial return link for acknowledgements. > > >At 04:05 PM 3/4/2002 -0500, Ouellette, Tim wrote: >>I have a question regarding # 2. >> >>let's say both routera and router b are connected and advertising the link >>between them to router c. The connection from routera to routerc is a 64k >>frame circuit. The link betwen routerb and routerc is a 64k ISDN (1 b). If >>routera advertises the network between itself and routerb with a cost of 10, >>and routerb advertises that same network with a cost of 100. All other >>things being equal when routerc gets the two updates, he will prefer to take >>the frame circuit towards routera to get to that network. Why would anyways >>want this? What if the circuit between routerb and routerc was a backup ISDN >>that you had to pay extra for to bring up during normal business hours or >>something like that. I guess it all comes down to what your network is >>doing. Whether two boxes advertise the same cost to a network is really only >>dependent upon which path you want to take to get there. If they both >>advertise the same, you may potentially load balance. If that's not desired, >>crank up the cost of one of those boxes so it's path is less-desirable. >> >>router a --- routerb >> \ / >> \ / >> \ / >> routerc >> >>Was I just rambling? Did that make sense. >> >>Tim >> >> >>-----Original Message----- >>From: Priscilla Oppenheimer [mailto:[EMAIL PROTECTED]] >>Sent: Monday, March 04, 2002 2:48 PM >>To: [EMAIL PROTECTED] >>Subject: Re: basic OSPF questions [7:37142] >> >> >>At 08:59 AM 3/4/02, bergenpeak wrote: >> >> >> >> >> >2) Must a link cost be the same on for all routers that share the >> >link? Is there a protocol reason for this? Some other reason? >> >>I couldn't find anything in RFC 2328 that says that two routers connected >>to a link MUST agree on the cost. The RFC writers use the term MUST >>carefully. If it were required, they would put it in the RFC. >> >>I think it would be a good idea to make them agree, though.... Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=37223&t=37142 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
