RE: OSPF Area virtual links
There seems to be one major advantage of using loopback addresses for OSPF-the highest loopback will be chosen for the RID and it stays up as long as the router is up and you can use any address you want. There are other advantages but not as significant as this. If you use a loopback address which is a legal IP address, and treat it like any other legal interface, you can ping and route to that interface from anywhere. If you use an unpublished address, you cannot ping or route to the interface from elsewhere. In the case of virtual links, it is advisable to use any physical interface IP address on the router. This allows the routers on either end of the link to find each other. It does not have to be the loopback interface. In fact it should not be the loopback interface unless you are using a legal router address for the loopback. Bottom Line: If you have addresses to spare, use a legal address for the loopback. If you do not have addresses to spare use an "unpublished" address. Do not advertise or distribute this address. Only the router on which it is configured should have it as a route(and RID). All others will see it only as an RID. For virtual links, any interface address configured on the router would do the trick. The OSPF routers configured with the statement know what to do with the packets regardless of which interface it comes in on. Of course it may be better to choose the interfaces which are closest to each other. This does not cover every possible scenario, but in the special case of virtual links, it is not necessary to do static or advertise the loopback. Winston. -Original Message- From: Keith Townsend [mailto:[EMAIL PROTECTED]] Sent: Thursday, November 09, 2000 8:01 PM To: [EMAIL PROTECTED] Subject: OSPF Area virtual links When creating a virtual link between an ABR non-directly connected are to an ABR in the backbone should you always use the loopback address for the virtual link. Doyle does this on page 943 of his Routing TCP/IP book. Secondly is there a route to the loopback of these two routers. Maybe I'm forgetting something but how do the two routers find routes to each other if you're not advertising L0 and there is no static routes to the L0. Thanks, Keith _ 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]
Re: OSPF Area virtual links
You use the router ID of the remote router in the virtual link command. This will be the highest IP on a loopback interface. If you have multiple routers in a area use the show ip ospf commands to find out what the router ID is the router is forming an adjanency with, and used that for the virtual link command otherwise it will not come up. You should also reboot or stop your process and restart it so the OSPF process's and router IDs are correct. This way if you set up a virtual link on a new configuration and don't reboot and get it working, then go away... and at a later time the router reboots your virtual link router ID is correct. - Keith Townsend [EMAIL PROTECTED] wrote: When creating a virtual link between an ABR non-directly connected are to an ABR in the backbone should you always use the loopback address for the virtual link. Doyle does this on page 943 of his Routing TCP/IP book. Secondly is there a route to the loopback of these two routers. Maybe I'm forgetting something but how do the two routers find routes to each other if you're not advertising L0 and there is no static routes to the L0. Thanks, Keith _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] __ Do You Yahoo!? Thousands of Stores. Millions of Products. All in one Place. http://shopping.yahoo.com/ _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: OSPF Area virtual links
On Thu, 9 Nov 2000, Keith Townsend wrote: When creating a virtual link between an ABR non-directly connected are to an ABR in the backbone should you always use the loopback address for the virtual link. Doyle does this on page 943 of his Routing TCP/IP book. loopbacks are always good to use for terminating things like that. Secondly is there a route to the loopback of these two routers. Maybe I'm forgetting something but how do the two routers find routes to each other if you're not advertising L0 and there is no static routes to the L0. you would of course need to advertise the l0 via a routing protocol, or like you say, make static routes. Brian Thanks, Keith _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] --- Brian Feeny, CCNP, CCDP [EMAIL PROTECTED] Network Administrator ShreveNet Inc. (ASN 11881) _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: OSPF Area virtual links
The connection is actually from OSPF router ID ( RID ) to router i.d. In the case of Doyle, his example is so nicely numbered that the RIDs and the loopback addresses are the same. ;- I am guessing that this is one of the gotcha's that evil lab proctors might throw into the break-fix, or maybe one of the gotcha's that may cause the loss of points in the early phases of the lab. In the CCIE Lab prep advice I have been circulating www.chuck.to/CCIEAdvice.txt ) two different CCIE's mention the value of preparing a solid IP addressing scheme prior to beginning lab configuration. One of them warns about issues like changing RID's when routers are reloaded during the lab ( and in real life too :- ) Chuck -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of Keith Townsend Sent: Thursday, November 09, 2000 11:01 AM To: [EMAIL PROTECTED] Subject:OSPF Area virtual links When creating a virtual link between an ABR non-directly connected are to an ABR in the backbone should you always use the loopback address for the virtual link. Doyle does this on page 943 of his Routing TCP/IP book. Secondly is there a route to the loopback of these two routers. Maybe I'm forgetting something but how do the two routers find routes to each other if you're not advertising L0 and there is no static routes to the L0. Thanks, Keith _ 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]
RE: OSPF Area virtual links
Keith, Generally the router being used to connect you to area 0 will be on the same subnet. Therefore no routing issues. As far as loopback you have to use the router ID as the IP address of the router so if you are using a loopback address to be the router ID that would explain it. Cory -Original Message- From: Keith Townsend [mailto:[EMAIL PROTECTED]] Sent: Thursday, November 09, 2000 1:01 PM To: [EMAIL PROTECTED] Subject: OSPF Area virtual links When creating a virtual link between an ABR non-directly connected are to an ABR in the backbone should you always use the loopback address for the virtual link. Doyle does this on page 943 of his Routing TCP/IP book. Secondly is there a route to the loopback of these two routers. Maybe I'm forgetting something but how do the two routers find routes to each other if you're not advertising L0 and there is no static routes to the L0. Thanks, Keith _ 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]
