Single area with large number networks.
Hi, this question is really confuse me : What are two possible problems that can occur when a single OSPF area includes a large number of networks? a. more reachable errors b. frequent routing table recalculation c. frequent adjacencies table recalculation d. excessive link- state entries in the link- state table The frequent routing table recalculation is true, but what about the other one ? thanks, Ibrahim Disclaimer: Please note that this correspondence is for the named person's use only and may contain information that is confidential and privileged. If you received this correspondence in error, please immediately delete it from your system and notify the sender. Please ensure that you do not disclose, copy or rely on any part of this correspondence if you are not the intended recipient. We apologize for any inconvenience and thank you for your assistance. Please note that nothing in this correspondence shall be construed or otherwise relied upon by the recipient as an offer, acceptance of an offer, representation, agreement or resolution of any kind. Copyright(C)Davnet Singapore Pte. Ltd. 2000 winmail.dat
Single area with large number networks.
Hi, this question is really confuse me : What are two possible problems that can occur when a single OSPF area includes a large number of networks? a. more reachable errors b. frequent routing table recalculation c. frequent adjacencies table recalculation d. excessive link- state entries in the link- state table The frequent routing table recalculation is true, but what about the other one ? thanks, Ibrahim Disclaimer: Please note that this correspondence is for the named person's use only and may contain information that is confidential and privileged. If you received this correspondence in error, please immediately delete it from your system and notify the sender. Please ensure that you do not disclose, copy or rely on any part of this correspondence if you are not the intended recipient. We apologize for any inconvenience and thank you for your assistance. Please note that nothing in this correspondence shall be construed or otherwise relied upon by the recipient as an offer, acceptance of an offer, representation, agreement or resolution of any kind. Copyright(C)Davnet Singapore Pte. Ltd. 2000 winmail.dat
Re: Single area with large number networks.
Try this http://www.cisco.com/public/pubsearch.html - Original Message - From: "Ibrahim" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Tuesday, November 14, 2000 11:52 PM Subject: Single area with large number networks. > > Hi, this question is really confuse me : > What are two possible problems that can occur when a single OSPF area > includes a large number of networks? > a. more reachable errors > b. frequent routing table recalculation > c. frequent adjacencies table recalculation > d. excessive link- state entries in the link- state table > The frequent routing table recalculation is true, but what about the other > one ? > > thanks, > Ibrahim > > > > Disclaimer: > Please note that this correspondence is for the named person's use only and > may contain information that is confidential and privileged. If you received > this correspondence in error, please immediately delete it from your system > and notify the sender. Please ensure that you do not disclose, copy or rely > on any part of this correspondence if you are not the intended recipient. > We apologize for any inconvenience and thank you for your assistance. Please > note that nothing in this correspondence shall be construed or otherwise > relied upon by the recipient as an offer, acceptance of an offer, > representation, agreement or resolution of any kind. > > Copyright(C)Davnet Singapore Pte. Ltd. 2000 > > _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Single area with large number networks.
doesn't help. I tried before. I also opened the CCIE : TCP/IP routing book, ACRC book .. but can't found the answer. Ibam > > Try this > http://www.cisco.com/public/pubsearch.html > > - Original Message - > From: "Ibrahim" <[EMAIL PROTECTED]> > To: <[EMAIL PROTECTED]> > Sent: Tuesday, November 14, 2000 11:52 PM > Subject: Single area with large number networks. > > > > > > Hi, this question is really confuse me : > > What are two possible problems that can occur when a single OSPF area > > includes a large number of networks? > > a. more reachable errors > > b. frequent routing table recalculation > > c. frequent adjacencies table recalculation > > d. excessive link- state entries in the link- state table > > The frequent routing table recalculation is true, but what > about the other > > one ? > > > > thanks, > > Ibrahim > > > > > > > > Disclaimer: > > Please note that this correspondence is for the named person's use only > and > > may contain information that is confidential and privileged. If you > received > > this correspondence in error, please immediately delete it from your > system > > and notify the sender. Please ensure that you do not disclose, copy or > rely > > on any part of this correspondence if you are not the intended > recipient. > > We apologize for any inconvenience and thank you for your assistance. > Please > > note that nothing in this correspondence shall be construed or otherwise > > relied upon by the recipient as an offer, acceptance of an offer, > > representation, agreement or resolution of any kind. > > > > Copyright(C)Davnet Singapore Pte. Ltd. 2000 > > > > _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Single area with large number networks.
There are far better minds than mine, on this list , that defer to www.cisco.com as the definitive resource , this makes complete sense for obvious reasons. If you simply require an answer to your question I can provide you with that and also a whole swag of logical arguements and reasoning behind why I'm sure I'm correct. The thing is , I could be wrong either way how do you benefit from it ? - Original Message - From: "Ibrahim" <[EMAIL PROTECTED]> To: "Kane" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> Sent: Wednesday, November 15, 2000 1:02 AM Subject: RE: Single area with large number networks. > > > doesn't help. I tried before. I also opened the CCIE : TCP/IP routing book, > ACRC book .. but can't found the answer. > > > Ibam > > > > > Try this > > http://www.cisco.com/public/pubsearch.html > > > > - Original Message - > > From: "Ibrahim" <[EMAIL PROTECTED]> > > To: <[EMAIL PROTECTED]> > > Sent: Tuesday, November 14, 2000 11:52 PM > > Subject: Single area with large number networks. > > > > > > > > > > Hi, this question is really confuse me : > > > What are two possible problems that can occur when a single OSPF area > > > includes a large number of networks? > > > a. more reachable errors > > > b. frequent routing table recalculation > > > c. frequent adjacencies table recalculation > > > d. excessive link- state entries in the link- state table > > > The frequent routing table recalculation is true, but what > > about the other > > > one ? > > > > > > thanks, > > > Ibrahim > > > > > > > > > > > > Disclaimer: > > > Please note that this correspondence is for the named person's use only > > and > > > may contain information that is confidential and privileged. If you > > received > > > this correspondence in error, please immediately delete it from your > > system > > > and notify the sender. Please ensure that you do not disclose, copy or > > rely > > > on any part of this correspondence if you are not the intended > > recipient. > > > We apologize for any inconvenience and thank you for your assistance. > > Please > > > note that nothing in this correspondence shall be construed or otherwise > > > relied upon by the recipient as an offer, acceptance of an offer, > > > representation, agreement or resolution of any kind. > > > > > > Copyright(C)Davnet Singapore Pte. Ltd. 2000 > > > > > > > > _ > 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: Single area with large number networks.
IMHO, B is the best answer as link failures in the area will cause recalculations. D is a possible answer; however, "excessive" is a subjective word: OSPF will generate the number of LSAs necessary to build its tables and the picture of the network: it will not go beyond the number needed to do so. On the other hand, as a human, I may find a large number of LSAs "excessive". HTH, Charles D is kind of subjective, but it ""Ibrahim"" <[EMAIL PROTECTED]> wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > doesn't help. I tried before. I also opened the CCIE : TCP/IP routing book, > ACRC book .. but can't found the answer. > > > Ibam > > > > > Try this > > http://www.cisco.com/public/pubsearch.html > > > > - Original Message - > > From: "Ibrahim" <[EMAIL PROTECTED]> > > To: <[EMAIL PROTECTED]> > > Sent: Tuesday, November 14, 2000 11:52 PM > > Subject: Single area with large number networks. > > > > > > > > > > Hi, this question is really confuse me : > > > What are two possible problems that can occur when a single OSPF area > > > includes a large number of networks? > > > a. more reachable errors > > > b. frequent routing table recalculation > > > c. frequent adjacencies table recalculation > > > d. excessive link- state entries in the link- state table > > > The frequent routing table recalculation is true, but what > > about the other > > > one ? > > > > > > thanks, > > > Ibrahim > > > > > > > > > > > > Disclaimer: > > > Please note that this correspondence is for the named person's use only > > and > > > may contain information that is confidential and privileged. If you > > received > > > this correspondence in error, please immediately delete it from your > > system > > > and notify the sender. Please ensure that you do not disclose, copy or > > rely > > > on any part of this correspondence if you are not the intended > > recipient. > > > We apologize for any inconvenience and thank you for your assistance. > > Please > > > note that nothing in this correspondence shall be construed or otherwise > > > relied upon by the recipient as an offer, acceptance of an offer, > > > representation, agreement or resolution of any kind. > > > > > > Copyright(C)Davnet Singapore Pte. Ltd. 2000 > > > > > > > > _ > 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: Single area with large number networks.
if you said refer to www.cisco.com, why everybody still need this mailing-list ? why there are many questions in this group ? Or better just simple make auto replay answer in this group "go to cisco website, you'll find the answer". :-) Ibrahim > There are far better minds than mine, on this list , that defer to > www.cisco.com as the definitive resource , this makes complete sense for > obvious reasons. If you simply require an answer to your question I can > provide you with that and also a whole swag of logical arguements and > reasoning behind why I'm sure I'm correct. The thing is , I could be > wrong either way how do you benefit from it ? > > > - Original Message - > From: "Ibrahim" <[EMAIL PROTECTED]> > To: "Kane" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> > Sent: Wednesday, November 15, 2000 1:02 AM > Subject: RE: Single area with large number networks. > > > > > > > > doesn't help. I tried before. I also opened the CCIE : TCP/IP routing > book, > > ACRC book .. but can't found the answer. > > > > > > Ibam > > > > > > > > Try this > > > http://www.cisco.com/public/pubsearch.html > > > > > > - Original Message - > > > From: "Ibrahim" <[EMAIL PROTECTED]> > > > To: <[EMAIL PROTECTED]> > > > Sent: Tuesday, November 14, 2000 11:52 PM > > > Subject: Single area with large number networks. > > > > > > > > > > > > > > Hi, this question is really confuse me : > > > > What are two possible problems that can occur when a single > OSPF area > > > > includes a large number of networks? > > > > a. more reachable errors > > > > b. frequent routing table recalculation > > > > c. frequent adjacencies table recalculation > > > > d. excessive link- state entries in the link- state table > > > > The frequent routing table recalculation is true, but what > > > about the other > > > > one ? > > > > > > > > thanks, > > > > Ibrahim > > > > > > > > > > > > > > > > Disclaimer: > > > > Please note that this correspondence is for the named person's use > only > > > and > > > > may contain information that is confidential and privileged. If you > > > received > > > > this correspondence in error, please immediately delete it from your > > > system > > > > and notify the sender. Please ensure that you do not > disclose, copy or > > > rely > > > > on any part of this correspondence if you are not the intended > > > recipient. > > > > We apologize for any inconvenience and thank you for your > assistance. > > > Please > > > > note that nothing in this correspondence shall be construed or > otherwise > > > > relied upon by the recipient as an offer, acceptance of an offer, > > > > representation, agreement or resolution of any kind. > > > > > > > > Copyright(C)Davnet Singapore Pte. Ltd. 2000 > > > > > > > > > > > > _ > > 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: Single area with large number networks.
thanks for your response. But if some router down, the nearest one will send message to DR & BDR, and DR will send multicast message (it won't be excessive) to its networks. thanks, Ibrahim > > IMHO, B is the best answer as link failures in the area will cause > recalculations. > > D is a possible answer; however, "excessive" is a subjective word: OSPF > will generate the number of LSAs necessary to build its tables and the > picture of the network: it will not go beyond the number needed to do so. > On the other hand, as a human, I may find a large number of LSAs > "excessive". > > HTH, > > Charles > > D is kind of subjective, but it > ""Ibrahim"" <[EMAIL PROTECTED]> wrote in message > [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > > > > doesn't help. I tried before. I also opened the CCIE : TCP/IP routing > book, > > ACRC book .. but can't found the answer. > > > > > > Ibam > > > > > > > > Try this > > > http://www.cisco.com/public/pubsearch.html > > > > > > - Original Message - > > > From: "Ibrahim" <[EMAIL PROTECTED]> > > > To: <[EMAIL PROTECTED]> > > > Sent: Tuesday, November 14, 2000 11:52 PM > > > Subject: Single area with large number networks. > > > > > > > > > > > > > > Hi, this question is really confuse me : > > > > What are two possible problems that can occur when a single > OSPF area > > > > includes a large number of networks? > > > > a. more reachable errors > > > > b. frequent routing table recalculation > > > > c. frequent adjacencies table recalculation > > > > d. excessive link- state entries in the link- state table > > > > The frequent routing table recalculation is true, but what > > > about the other > > > > one ? > > > > > > > > thanks, > > > > Ibrahim > > > > > > > > > > > > > > > > Disclaimer: > > > > Please note that this correspondence is for the named person's use > only > > > and > > > > may contain information that is confidential and privileged. If you > > > received > > > > this correspondence in error, please immediately delete it from your > > > system > > > > and notify the sender. Please ensure that you do not > disclose, copy or > > > rely > > > > on any part of this correspondence if you are not the intended > > > recipient. > > > > We apologize for any inconvenience and thank you for your > assistance. > > > Please > > > > note that nothing in this correspondence shall be construed or > otherwise > > > > relied upon by the recipient as an offer, acceptance of an offer, > > > > representation, agreement or resolution of any kind. > > > > > > > > Copyright(C)Davnet Singapore Pte. Ltd. 2000 > > > > > > > > > > > > _ > > 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] _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: Single area with large number networks.
Opinions vary , however my understanding is that this is a forum. "Why does everyone need this mailing list"? I don't know that everyone does , I participate because I enjoy it. You answered the rest yourself... - Original Message - From: "Ibrahim" <[EMAIL PROTECTED]> To: "Kane" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> Sent: Wednesday, November 15, 2000 2:31 AM Subject: RE: Single area with large number networks. > > > if you said refer to www.cisco.com, why everybody still need this > mailing-list ? why there are many questions in this group ? Or better just > simple make auto replay answer in this group "go to cisco website, you'll > find the answer". :-) > > > > Ibrahim > > > There are far better minds than mine, on this list , that defer to > > www.cisco.com as the definitive resource , this makes complete sense for > > obvious reasons. If you simply require an answer to your question I can > > provide you with that and also a whole swag of logical arguements and > > reasoning behind why I'm sure I'm correct. The thing is , I could be > > wrong either way how do you benefit from it ? > > > > > > - Original Message - > > From: "Ibrahim" <[EMAIL PROTECTED]> > > To: "Kane" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> > > Sent: Wednesday, November 15, 2000 1:02 AM > > Subject: RE: Single area with large number networks. > > > > > > > > > > > > > doesn't help. I tried before. I also opened the CCIE : TCP/IP routing > > book, > > > ACRC book .. but can't found the answer. > > > > > > > > > Ibam > > > > > > > > > > > Try this > > > > http://www.cisco.com/public/pubsearch.html > > > > > > > > - Original Message - > > > > From: "Ibrahim" <[EMAIL PROTECTED]> > > > > To: <[EMAIL PROTECTED]> > > > > Sent: Tuesday, November 14, 2000 11:52 PM > > > > Subject: Single area with large number networks. > > > > > > > > > > > > > > > > > > Hi, this question is really confuse me : > > > > > What are two possible problems that can occur when a single > > OSPF area > > > > > includes a large number of networks? > > > > > a. more reachable errors > > > > > b. frequent routing table recalculation > > > > > c. frequent adjacencies table recalculation > > > > > d. excessive link- state entries in the link- state table > > > > > The frequent routing table recalculation is true, but what > > > > about the other > > > > > one ? > > > > > > > > > > thanks, > > > > > Ibrahim > > > > > > > > > > > > > > > > > > > > Disclaimer: > > > > > Please note that this correspondence is for the named person's use > > only > > > > and > > > > > may contain information that is confidential and privileged. If you > > > > received > > > > > this correspondence in error, please immediately delete it from your > > > > system > > > > > and notify the sender. Please ensure that you do not > > disclose, copy or > > > > rely > > > > > on any part of this correspondence if you are not the intended > > > > recipient. > > > > > We apologize for any inconvenience and thank you for your > > assistance. > > > > Please > > > > > note that nothing in this correspondence shall be construed or > > otherwise > > > > > relied upon by the recipient as an offer, acceptance of an offer, > > > > > representation, agreement or resolution of any kind. > > > > > > > > > > Copyright(C)Davnet Singapore Pte. Ltd. 2000 > > > > > > > > > > > > > > > > _ > > > 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: Single area with large number networks.
Given the context and the choices, I would have to pick B and D as well. The routing table recalculation isn't really a great answer either. Suppose your links never go down, and once that last router is turned on and all the SPF's have been done. This sucker would remain pretty quiet. But... given that links do go down, routers go off line and back on, etc, yes - routing table changes. So B D is to me the answer of last resort, one of those things Cisco loves in their tests. Let's look at the other answers: More reachable errors. Huh? What is a "reachable" error? Frequent adjacencies table updates - now this one has the ring of truth about it... Excessive link state entries in the link state database...this rings true also So of the two that ring true, which one is more correct? I would choose the excessive link state entries because in my reading from various resources I have seen expressed many times router capacity, memory requirements, processing power. This last one falls into that category. I don't ever recall reading about adjacency table updates, but I won't say it doesn't happen. Show ip ospf neighbor does sho adjacencies. but you are adjacent to only a small number of routers, no matter what the size of the network. So, A and D Test taking 101 - answering Cisco questions the Cisco way Chuck -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of Cthulu, CCIE Candidate Sent: Tuesday, November 14, 2000 5:33 AM To: [EMAIL PROTECTED] Subject: Re: Single area with large number networks. IMHO, B is the best answer as link failures in the area will cause recalculations. D is a possible answer; however, "excessive" is a subjective word: OSPF will generate the number of LSAs necessary to build its tables and the picture of the network: it will not go beyond the number needed to do so. On the other hand, as a human, I may find a large number of LSAs "excessive". HTH, Charles D is kind of subjective, but it > > From: "Ibrahim" <[EMAIL PROTECTED]> > > To: <[EMAIL PROTECTED]> > > Sent: Tuesday, November 14, 2000 11:52 PM > > Subject: Single area with large number networks. > > > > > Hi, this question is really confuse me : > > > What are two possible problems that can occur when a single OSPF area > > > includes a large number of networks? > > > a. more reachable errors > > > b. frequent routing table recalculation > > > c. frequent adjacencies table recalculation > > > d. excessive link- state entries in the link- state table > > > The frequent routing table recalculation is true, but what > > about the other > > > one ? > > > > > > thanks, > > > Ibrahim > > > > > > _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Single area with large number networks.
>"Ibrahim" <[EMAIL PROTECTED]> May I make some suggestions here? Learning to use the cisco website indeed is important, and indeed is not the only way. In this particular case, I don't think you will find the answer there. Why? Because there have been recent discussions on this list about OSPF sizing and on OSPF failure recovery. These discussions did require looking at the RFCs, and also some expert opinion that largely isn't written down. So, I'd say in this case, if there was an appropriate autoreply at all, it would have been "check the archives." My suggestion here would be to write why you think b is a correct answer, and what your thoughts are about each of the alternatives. But I do have some specific technical comments; see below. >if you said refer to www.cisco.com, why everybody still need this >mailing-list ? why there are many questions in this group ? Or better just >simple make auto replay answer in this group "go to cisco website, you'll >find the answer". :-) > >Ibrahim > >> There are far better minds than mine, on this list , that defer to >> www.cisco.com as the definitive resource , this makes complete sense for >> obvious reasons. If you simply require an answer to your question I can >> provide you with that and also a whole swag of logical arguements and >> reasoning behind why I'm sure I'm correct. The thing is , I could be >> wrong either way how do you benefit from it ? >> >> >> - Original Message - >> From: "Ibrahim" <[EMAIL PROTECTED]> >> To: "Kane" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> >> Sent: Wednesday, November 15, 2000 1:02 AM > > Subject: RE: Single area with large number networks. > > > > >> > >> > doesn't help. I tried before. I also opened the CCIE : TCP/IP routing >> book, >> > ACRC book .. but can't found the answer. >> > >> > >> > Ibam >> > >> > > >> > > Try this >> > > http://www.cisco.com/public/pubsearch.html >> > > >> > > - Original Message - >> > > From: "Ibrahim" <[EMAIL PROTECTED]> >> > > To: <[EMAIL PROTECTED]> >> > > Sent: Tuesday, November 14, 2000 11:52 PM >> > > Subject: Single area with large number networks. >> > > >> > > >> > > > >> > > > Hi, this question is really confuse me : >> > > > What are two possible problems that can occur when a single >> OSPF area >> > > > includes a large number of networks? >> > > > a. more reachable errors >> > > > b. frequent routing table recalculation >> > > > c. frequent adjacencies table recalculation >> > > > d. excessive link- state entries in the link- state table >> > > > The frequent routing table recalculation is true, but what >> > > about the other > > > > > one ? As to the specific question, I think it's poorly worded. I would say, however, there are three correct answers. a) If I assume that more networks and routers are present, then logically more can fail, requiring recomputation. There isn't any simple answer to sizing this, since it depends on the reliability of the networks and the CPU power of the routers in the area. b) If, by the routing table, they mean the area route calculation by OSPF, yes. What I think of the main routing table, however, is that which is shown with sho ip route, which is not the same as the transient OSPF topology table. NOT c): There is no such thing as an adjacency table. There is a neighbor table, which doesn't get recalculated unless a directly connected DR or BDR goes down. d) Well, yes. The more networks, the more LS entries. On the other hand, this isn't usually a major limitation. CPU power is more likely to be a resource limit. I wonder if the author of the question might have been thinking of the OSPF Database Overflow feature, which Cisco doesn't implement since iBGP handles that problem better. _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Single area with large number networks.
Telling someone to use the Cisco search engine for a question like this is not helpful. It was kind of funny, but also a bit cruel, and definitely a waste of bandwidth. Answer A "more reachable errors" is clearly wrong since it's nonsense. I think answer D is wrong also because an OSPF router doesn't really have a link-state database. It has a topology database. (I'm not an OSPF guru, but when trying to pass a test I look for cases where the test-writer garbled the terminology to make a wrong answer.) It's not really an easy question because the acceptable number of routers in an OSPF area depends on many things: How stable is the network? If the network is really stable, then OSPF doesn't do much. Routers send hellos to each other and that's about all that happens. How busy are the routers already? Are they approaching a CPU utilization that could cause problems if the shortest path first (Dijkstra) algorithm has to be run often because of network instabilities? How much memory does the router have to hold the topology database and other data structures? See the groupstudy archives for some good discussions by the Chucks on OSPF scalability. Priscilla > > > > Try this > > http://www.cisco.com/public/pubsearch.html > > > > - Original Message - > > From: "Ibrahim" <[EMAIL PROTECTED]> > > To: <[EMAIL PROTECTED]> > > Sent: Tuesday, November 14, 2000 11:52 PM > > Subject: Single area with large number networks. > > > > > > > > > > Hi, this question is really confuse me : > > > What are two possible problems that can occur when a single OSPF area > > > includes a large number of networks? > > > a. more reachable errors > > > b. frequent routing table recalculation > > > c. frequent adjacencies table recalculation > > > d. excessive link- state entries in the link- state table > > > The frequent routing table recalculation is true, but what > > about the other > > > one ? > > > > > > thanks, > > > Ibrahim > > > Priscilla Oppenheimer http://www.priscilla.com _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Single area with large number networks.
At 09:36 PM 11/14/00, Ibrahim wrote: >thanks for your response. >But if some router down, the nearest one will send message to DR & BDR, and >DR will send multicast message (it won't be excessive) to its networks. I agree it wouldn't be excessive. Within a LAN, the DR mechanism keeps adjancies and LSA propagation from getting excessive. Between areas, the number of LSAs would depend on summarization. So without more information on the network topology, addressing, and configuration, we couldn't even say when LSAs would be a problem. Besides, as I look more closely at the answer, I see that it says, "excessive link-state entries in the link-state table." What's a link-state table? I think the test writer put a few good-sounding words together to throw you off. Conclusion: D is wrong. This is the kind of thinking you should do to pass Cisco tests! &;-) Priscilla >thanks, >Ibrahim > > > > > IMHO, B is the best answer as link failures in the area will cause > > recalculations. > > > > D is a possible answer; however, "excessive" is a subjective word: OSPF > > will generate the number of LSAs necessary to build its tables and the > > picture of the network: it will not go beyond the number needed to do so. > > On the other hand, as a human, I may find a large number of LSAs > > "excessive". > > > > HTH, > > > > Charles > > > > D is kind of subjective, but it > > ""Ibrahim"" <[EMAIL PROTECTED]> wrote in message > > [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > > > > > > > doesn't help. I tried before. I also opened the CCIE : TCP/IP routing > > book, > > > ACRC book .. but can't found the answer. > > > > > > > > > Ibam > > > > > > > > > > > Try this > > > > http://www.cisco.com/public/pubsearch.html > > > > > > > > - Original Message - > > > > From: "Ibrahim" <[EMAIL PROTECTED]> > > > > To: <[EMAIL PROTECTED]> > > > > Sent: Tuesday, November 14, 2000 11:52 PM > > > > Subject: Single area with large number networks. > > > > > > > > > > > > > > > > > > Hi, this question is really confuse me : > > > > > What are two possible problems that can occur when a single > > OSPF area > > > > > includes a large number of networks? > > > > > a. more reachable errors > > > > > b. frequent routing table recalculation > > > > > c. frequent adjacencies table recalculation > > > > > d. excessive link- state entries in the link- state table > > > > > The frequent routing table recalculation is true, but what > > > > about the other > > > > > one ? > > > > > > > > > > thanks, > > > > > Ibrahim > > > > > > > > > > > > > > > > > > > > Disclaimer: > > > > > Please note that this correspondence is for the named person's use > > only > > > > and > > > > > may contain information that is confidential and privileged. If you > > > > received > > > > > this correspondence in error, please immediately delete it from your > > > > system > > > > > and notify the sender. Please ensure that you do not > > disclose, copy or > > > > rely > > > > > on any part of this correspondence if you are not the intended > > > > recipient. > > > > > We apologize for any inconvenience and thank you for your > > assistance. > > > > Please > > > > > note that nothing in this correspondence shall be construed or > > otherwise > > > > > relied upon by the recipient as an offer, acceptance of an offer, > > > > > representation, agreement or resolution of any kind. > > > > > > > > > > Copyright(C)Davnet Singapore Pte. Ltd. 2000 > > > > > > > > > > > > > > > > _ > > > 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] > >_ >FAQ, list archives, and subscription info: >http://www.groupstudy.com/list/cisco.html >Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Priscilla Oppenheimer http://www.priscilla.com _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Single area with large number networks.
At 11:11 AM 11/14/00 -0800, Priscilla Oppenheimer wrote: >Answer A "more reachable errors" is clearly wrong since it's nonsense. I >think answer D is wrong also because an OSPF router doesn't really have a >link-state database. It has a topology database. (I'm not an OSPF guru, >but when trying to pass a test I look for cases where the test-writer >garbled the terminology to make a wrong answer.) Hmm, Priscilla, I have to disagree with you here--RFC 2328 refers not to a "topology database," but to a "link-state database." I find many of the terms commonly used to describe OSPF are not precise, and it's important for those new to internetworking to be aware of this. "Topology database" and "link-state database" seem to be used interchangeably by some very knowledgeable folks, and I don't really think one is more correct than the other--after all, they both refer to a data structure that describes the topology of the OSPF internetwork for that area. The Cisco course materials tend to call it a "topology database," but I wouldn't be the one to suggest that makes the RFC incorrect. Here's another example: RFC 2328 refers to a "neighbor data structure," but it is almost always called an "adjacencies database," "neigbor table," or in more recent Cisco course materials, "neighborship database" when people write about it. All those terms mean the same thing--a place in the router's memory where it stores information about its neighbors. Radia Perlman has a nice rant on the topic of imprecise terminology in the 2nd edition of "Interconnections." Highly recommended, for those who haven't already seen it. ;-) Pamela _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Single area with large number networks.
But if the "right" answer consists of two choices... I believe we all agree that B - frequent routing recalculation - is "correct" I believe we all agree that A - more reachable errors - is BS Of the two remaining choices, which is least wrong? My reasoning was that C - frequent adjacency table recalculation - is irrelevant because an OSPF router forms adjacencies only with directly connected neighbors, and not necessarily with every router in the area. The result of the "show IP OSPF neighbor" command, even in very large networks, would be relatively small. That leaves D as being the other "correct" answer. Yeah, I see your point, Priscilla. On the other hand, all of us have seen a wide variety of terminology for the same think. Link state database, link state table, OSPF table, OSPF database, and so on. It is not unreasonable to conclude that the test writer has his or her own jargon for what we call the OSPF database. If D is wrong, then the choice is C, and that's problematic. Chuck -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of Priscilla Oppenheimer Sent: Tuesday, November 14, 2000 11:33 AM To: [EMAIL PROTECTED] Subject: RE: Single area with large number networks. At 09:36 PM 11/14/00, Ibrahim wrote: >thanks for your response. >But if some router down, the nearest one will send message to DR & BDR, and >DR will send multicast message (it won't be excessive) to its networks. I agree it wouldn't be excessive. Within a LAN, the DR mechanism keeps adjancies and LSA propagation from getting excessive. Between areas, the number of LSAs would depend on summarization. So without more information on the network topology, addressing, and configuration, we couldn't even say when LSAs would be a problem. Besides, as I look more closely at the answer, I see that it says, "excessive link-state entries in the link-state table." What's a link-state table? I think the test writer put a few good-sounding words together to throw you off. Conclusion: D is wrong. This is the kind of thinking you should do to pass Cisco tests! &;-) Priscilla >thanks, >Ibrahim > > > > > IMHO, B is the best answer as link failures in the area will cause > > recalculations. > > > > D is a possible answer; however, "excessive" is a subjective word: OSPF > > will generate the number of LSAs necessary to build its tables and the > > picture of the network: it will not go beyond the number needed to do so. > > On the other hand, as a human, I may find a large number of LSAs > > "excessive". > > > > HTH, > > > > Charles > > > > D is kind of subjective, but it > > ""Ibrahim"" <[EMAIL PROTECTED]> wrote in message > > [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > > > > > > > doesn't help. I tried before. I also opened the CCIE : TCP/IP routing > > book, > > > ACRC book .. but can't found the answer. > > > > > > > > > Ibam > > > > > > > > > > > Try this > > > > http://www.cisco.com/public/pubsearch.html > > > > > > > > - Original Message - > > > > From: "Ibrahim" <[EMAIL PROTECTED]> > > > > To: <[EMAIL PROTECTED]> > > > > Sent: Tuesday, November 14, 2000 11:52 PM > > > > Subject: Single area with large number networks. > > > > > > > > > > > > > > > > > > Hi, this question is really confuse me : > > > > > What are two possible problems that can occur when a single > > OSPF area > > > > > includes a large number of networks? > > > > > a. more reachable errors > > > > > b. frequent routing table recalculation > > > > > c. frequent adjacencies table recalculation > > > > > d. excessive link- state entries in the link- state table > > > > > The frequent routing table recalculation is true, but what > > > > about the other > > > > > one ? > > > > > > > > > > thanks, > > > > > Ibrahim > > > > > > > > > > > > > > > > > > > > Disclaimer: > > > > > Please note that this correspondence is for the named person's use > > only > > > > and > > > > > may contain information that is confidential and privileged. If you > > > > received > > > > > this correspondence in error, please immedia
RE: Single area with large number networks.
In defence of my earlier position that "d" is in fact the other correct answer. "Priscilla's Point: >Besides, as I look more closely at the answer, I see that it says, >"excessive link-state entries in the link-state table." What's a link-state >table? I think the test writer put a few good-sounding words together to >throw you off. > >Conclusion: D is wrong. > I would argue that that RFC 2328 describes the repository for link/state information as the link state database. I personally feel that a substitution of database for table is acceptable. I think we would all agree, that a large number of prefix's would lead to a proportionally large table/database of link states. Here is an excerpt from 2328 "The collected link state advertisements of all routers and networks forms the protocol's link state database." However, if D is wrong, which of the other 2 are right? I would tend to think that D is the least wrong of the three remaining choices. Overall, I think this is another example of technical lack of precision leading to unnecessary ambiguity. Pete _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: Single area with large number networks.
My vote goes to D (and B, but I don't think that's under dispute). OK, so 'excessive' is subjective, but then so is 'large'. The question's not asking WHEN the problems will occur, or even claiming that problems will occur in all circumstances, just asking what POSSIBLE problems there are. My reasoning is that as the number of networks increases, the number of LSAs increases, but the number of adjacencies each router has doesn't necessarily increase (by much). The question implies single OSPF area, so summarisation doesn't come into the picture. Given a finite amount of memory, CPU etc on routers, a 'large' number of networks will cause a 'large' number of LSAs, which have to be refreshed every 30 minutes regardless of network changes, which causes traffic, CPU usage, etc - and potential problems. Especially if you interpret 'large' as 'large enough to cause problems'. JMcL -- Forwarded by Jenny Mcleod/NSO/CSDA on 15/11/2000 09:24 am --- "Chuck Larrieu" <[EMAIL PROTECTED]> on 15/11/2000 07:11:13 am Please respond to "Chuck Larrieu" <[EMAIL PROTECTED]> To: "Priscilla Oppenheimer" <[EMAIL PROTECTED]> [EMAIL PROTECTED] cc:(bcc: JENNY MCLEOD/NSO/CSDA) Subject: RE: Single area with large number networks. But if the "right" answer consists of two choices... I believe we all agree that B - frequent routing recalculation - is "correct" I believe we all agree that A - more reachable errors - is BS Of the two remaining choices, which is least wrong? My reasoning was that C - frequent adjacency table recalculation - is irrelevant because an OSPF router forms adjacencies only with directly connected neighbors, and not necessarily with every router in the area. The result of the "show IP OSPF neighbor" command, even in very large networks, would be relatively small. That leaves D as being the other "correct" answer. Yeah, I see your point, Priscilla. On the other hand, all of us have seen a wide variety of terminology for the same think. Link state database, link state table, OSPF table, OSPF database, and so on. It is not unreasonable to conclude that the test writer has his or her own jargon for what we call the OSPF database. If D is wrong, then the choice is C, and that's problematic. Chuck -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of Priscilla Oppenheimer Sent: Tuesday, November 14, 2000 11:33 AM To: [EMAIL PROTECTED] Subject: RE: Single area with large number networks. At 09:36 PM 11/14/00, Ibrahim wrote: >thanks for your response. >But if some router down, the nearest one will send message to DR & BDR, and >DR will send multicast message (it won't be excessive) to its networks. I agree it wouldn't be excessive. Within a LAN, the DR mechanism keeps adjancies and LSA propagation from getting excessive. Between areas, the number of LSAs would depend on summarization. So without more information on the network topology, addressing, and configuration, we couldn't even say when LSAs would be a problem. Besides, as I look more closely at the answer, I see that it says, "excessive link-state entries in the link-state table." What's a link-state table? I think the test writer put a few good-sounding words together to throw you off. Conclusion: D is wrong. This is the kind of thinking you should do to pass Cisco tests! &;-) Priscilla >thanks, >Ibrahim > > > > > IMHO, B is the best answer as link failures in the area will cause > > recalculations. > > > > D is a possible answer; however, "excessive" is a subjective word: OSPF > > will generate the number of LSAs necessary to build its tables and the > > picture of the network: it will not go beyond the number needed to do so. > > On the other hand, as a human, I may find a large number of LSAs > > "excessive". > > > > HTH, > > > > Charles > > > > D is kind of subjective, but it > > ""Ibrahim"" <[EMAIL PROTECTED]> wrote in message > > [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > > > > > > > doesn't help. I tried before. I also opened the CCIE : TCP/IP routing > > book, > > > ACRC book .. but can't found the answer. > > > > > > > > > Ibam > > > > > > > > > > > Try this > > > > http://www.cisco.com/public/pubsearch.html > > > > > > > > - Original Message - > > > > From: "Ibrahim" <[EMAIL PROTECTED]> > > > > To: <[EMAIL PROTECTED]> &
RE: Single area with large number networks.
OK, I now think the right answer is B and D also. Jenny, Pamela, and Howard have convinced me. As Howard said, Answer C, "frequent adjacencies table recalculation" is even more BS than Answer D, "excessive link-state entries in the link-state table." There's no such thing as an adjacency table. There is a neighbor table, but it doesn't get recalculated unless a directly-connected DR or BDR goes down, which doesn't happen that often. In Answer D, they probably just meant link-state database, which is another term for "topology database," as Pamela pointed out. And Jenny and others pointed out that as the number of networks in an area increases, the number of LSAs increases, but the number of adjacencies each router has doesn't necessarily increase. So we should be looking for a right answer that talks about scaling links, not adjacencies. So D is right. B is also marginally right. A is definitely wrong. C is probably wrong too. Anyway, it's probably silly to be arguing over which answer is more wrong! &;-) I think the only thing we can conclude is that you would not have been able to find the answer by going to Cisco's search engine and this discussion was very worthwhile. Priscilla > > > > > - Original Message - > > > > > From: "Ibrahim" <[EMAIL PROTECTED]> > > > > > To: <[EMAIL PROTECTED]> > > > > > Sent: Tuesday, November 14, 2000 11:52 PM > > > > > Subject: Single area with large number networks. > > > > > > > > > > > > > > > > > > > > > > Hi, this question is really confuse me : > > > > > > What are two possible problems that can occur when a single > > > OSPF area > > > > > > includes a large number of networks? > > > > > > a. more reachable errors > > > > > > b. frequent routing table recalculation > > > > > > c. frequent adjacencies table recalculation > > > > > > d. excessive link- state entries in the link- state table > > > > > > The frequent routing table recalculation is true, but what > > > > > about the other > > > > > > one ? > > > > > > > > > > > > thanks, > > > > > > Ibrahim > > > > > > > > > > > > Priscilla Oppenheimer http://www.priscilla.com _ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
