There is a reason for the first one that I have seen. If for some reason you are using your loopback subnet for a NAT pool, and the NAT pool requires more than one global IP address, you can assign a /29 (or whatever) to the loopback and use that whole range for the NAT pool. That is one instance in which you may want to advertise more than a host route for your loopback. You could have loopback 1 as the RID, and loopback 2 assigned the /29 for NAT, loopback 2 would have the "ip ospf network point-to-point" command to advertise the /29.
-----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: >1) A loopback address is normally advertised by OSPF as a host route. >The command "ip ospf network point-to-point" enables one to specify >that the interface should be advertised as a subnet route. What are >the benefits for doing this? I can't imagine any benefits. Where did you find this info?? I do see some mention in RFC 2328 of using a host versus a subnet for the Link ID. "On point-to-point networks, if the neighbor's IP address is known, set the Link ID of the Type 3 link to the neighbor's IP address, and the Link Data to the mask 0xffffffff (indicating a host route).... If a subnet has been assigned to the point-to-point link, set the Link ID of the Type 3 link to the subnet's IP address, and the Link Data to the subnet's mask..." >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.... >3) In the Exstart phase, how is the master selected? Chappel's >book says RID while Doyle's say highest interface IP address. Which >is it? The router with the higher Router ID becomes the master. >4) I'm somewhat unclear on the Exchange and the Loading states. When >a router goes into Exchange state, does it send all DDPs it knows >about before processing any DDPs received from other adjancent >neighbors? I think so, but I've never thought about the database synchronization issues associated with a router that is a neighbor to many routers. My guess is that it can only be in the exchange state with one router at a time. Otherwise it would be exchanging database info with one router as the info was being updated by another router?? >Thus, a router goes into Exchange state, sends all DDPs it knows about, >then goes into Loading state, where it issues LSRs for LSAs it wants >more >details on? Is this the process? Sounds right. See the RFC for the details. >5) Is there a difference between DBD and DDP packets? I would avoid the term DDP, since it means Datagram Delivery Protocol to AppleTalk people. ;-) >Thanks ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=37191&t=37142 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]