RE: [Doyle on OSPF - Virtual Links [7:21658]
Chuck, Also remember that in a perfect world, virtual links are only meant to be a quick fix and, in most network designs, they are not an acceptable standard. My .02c, Rob H.NP, DP, blah,blah,blah. 1 of 48 Subj: RE: [Doyle on OSPF - Virtual Links [7:21658] Date: Tue, 2 Oct 2001 8:35:54 PM Eastern Daylight Time From: Chuck Larrieu To: [EMAIL PROTECTED] RFC 1793 discusses demand circuits in detail. I suspect but don not know for sure that virtual circuits are treated as demand circuits for a couple of reasons. A virtual circuit can traverse a bunch of routers from point of termination. The designers were sensitive to the added traffic that LSA's and hellos would add. Remember that the design work was done back in the days when a T1 was the greatest thing on earth, and 56K was common in WAN backbones. Also, it might be that the designers were thinking that virtual links might actually take place over dial up connections. for example, if I have a small dial up branch office in another state, I have them dial up to the nearest ( least costly ) branch office, rather than dial directly to my HQ site. Chuck -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Curtis Call Sent: Tuesday, October 02, 2001 7:36 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 Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=21838t=21658 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: [Doyle on OSPF - Virtual Links [7:21658]
funny how this quick fix holds a such a place of prominence in the standard ;- Chuck -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] Sent: Wednesday, October 03, 2001 6:03 AM To: [EMAIL PROTECTED]; [EMAIL PROTECTED] Subject: RE: [Doyle on OSPF - Virtual Links [7:21658] Chuck, Also remember that in a perfect world, virtual links are only meant to be a quick fix and, in most network designs, they are not an acceptable standard. My .02c, Rob H.NP, DP, blah,blah,blah. 1 of 48 Subj: RE: [Doyle on OSPF - Virtual Links [7:21658] Date: Tue, 2 Oct 2001 8:35:54 PM Eastern Daylight Time From: Chuck Larrieu To: [EMAIL PROTECTED] RFC 1793 discusses demand circuits in detail. I suspect but don not know for sure that virtual circuits are treated as demand circuits for a couple of reasons. A virtual circuit can traverse a bunch of routers from point of termination. The designers were sensitive to the added traffic that LSA's and hellos would add. Remember that the design work was done back in the days when a T1 was the greatest thing on earth, and 56K was common in WAN backbones. Also, it might be that the designers were thinking that virtual links might actually take place over dial up connections. for example, if I have a small dial up branch office in another state, I have them dial up to the nearest ( least costly ) branch office, rather than dial directly to my HQ site. Chuck -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Curtis Call Sent: Tuesday, October 02, 2001 7:36 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 Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=21992t=21658 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
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=7i=21665t=21658 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: [Re: [Doyle on OSPF - Virtual Links [7:21658]
Sorry, I meant to say that it is a requirement for a router that supports demand circuits to always attempt to make virtual- links act as demand circuits. 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 Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=21684t=21658 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: [Doyle on OSPF - Virtual Links [7:21658]
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=7i=21706t=21658 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: [Doyle on OSPF - Virtual Links [7:21658]
RFC 1793 discusses demand circuits in detail. I suspect but don not know for sure that virtual circuits are treated as demand circuits for a couple of reasons. A virtual circuit can traverse a bunch of routers from point of termination. The designers were sensitive to the added traffic that LSA's and hellos would add. Remember that the design work was done back in the days when a T1 was the greatest thing on earth, and 56K was common in WAN backbones. Also, it might be that the designers were thinking that virtual links might actually take place over dial up connections. for example, if I have a small dial up branch office in another state, I have them dial up to the nearest ( least costly ) branch office, rather than dial directly to my HQ site. Chuck -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Curtis Call Sent: Tuesday, October 02, 2001 7:36 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=7i=21758t=21658 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
