Thanks for the reply and the CCO link. I do remember now reading up On this feature, now all I need to do is set this up at home using An ISDN simulator to see exactly what OSPF-related packets go through.
Elmer -----Original Message----- From: Curtis Call [mailto:[EMAIL PROTECTED]] Sent: Tuesday, October 02, 2001 10:36 AM To: [EMAIL PROTECTED] Subject: Re: [Doyle on OSPF - Virtual Links [7:21658] This is referring to the fact that the virtual-link is being treated as a Demand Circuit. I don't believe that Doyle spoke much about this in his book, but I could be wrong. A Demand Circuit is used for low-bandwidth links such as ISDN to limit the uptime required for the link, this is done in two ways, first Hellos are suppressed between the two endpoints, and second LSAs are not sent when they expire, instead they are marked as DoNotAge LSAs which act just like they sound, they don't age. These two features are independent of each other, so for instance you could have a demand circuit that is suppressing Hellos, but isn't sending DoNotAge LSAs (so the LSAs will still need to be refreshed) or you could theoretically have a demand circuit that isn't suppressing Hellos, but is sending DoNotAge LSAs. In your situation, the link is suppressing Hellos as it states, but is not sending DoNotAge LSAs. This indicates that somewhere in your OSPF domain there is a router that doesn't support these LSAs, so the router is not allowed to generate them. It is a requirement for a router that supports virtual-links to always try to make it a demand circuit, so Cisco routers will always attempt to suppress Hellos over virtual links. For more info you could check out: http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr _c/ipcprt2/1cfospf.htm#xtocid2773922 For even better, go to the source: http://www.ietf.org/rfc/rfc1793.txt "Elmer Deloso" wrote: > Hi. > On Routing TCP/IP's page 555 there is an output of "show ip ospf > virtual-link" > That has these two info: > 1. DoNotAge LSA not allowed > 2. Adjacency State FULL (Hello suppressed) > Can someone please explain why these show up in the virtual link info? > I must have missed the significance somehere in my studies because > I can't explain these to myself. > Thank you. > > Elmer Deloso ---------- [EMAIL PROTECTED] OSPF Practice Exam www.boson.com\tests\Advanced.htm Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=21706&t=21658 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
