Re: basic OSPF questions [7:37142]
Ah, a footnote. Who reads footnotes? ;-) Just kidding. Thanks for bringing it up. I learned a lot. Priscilla At 05:44 AM 3/5/02, bergenpeak wrote: >Hi Priscilla, > >The use of the "ip ospf network point-to-point" as a mechanism >to enable one to advertise the loopback address as a subnet route >is from Doyle (Routing TCP/IP V1), page 417, footnote 9. > > > > > >Priscilla Oppenheimer wrote: > > > > 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 0x (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 Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=37335&t=37142 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: basic OSPF questions [7:37142]
Hi Priscilla, The use of the "ip ospf network point-to-point" as a mechanism to enable one to advertise the loopback address as a subnet route is from Doyle (Routing TCP/IP V1), page 417, footnote 9. Priscilla Oppenheimer wrote: > > 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 0x (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=37255&t=37142 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: basic OSPF questions [7:37142]
Just a little note... The BSCN book mentions that the routers MUST agree on the cost of the link, however when performing the labs i had no problems whatsoever with OSPF-specific issues as a result of cost mismatch. And none of the OSPF labs caution you to double-check this "requirement". BTW - BSCN p.127 states... "all interfaces connected to the same link must agree on the link's cost." However, this is in reference to adjusting the cost for Cisco routers that are connected to non-Cisco routers that might use different methods to derive the metric. My conclusion is that this might have more to do with engineering traffic for the applications running over OSPF links. Correct me if I'm wrong. Elmer - Original Message - From: "Peter van Oene" To: Sent: Monday, March 04, 2002 9:39 PM Subject: RE: basic OSPF questions [7:37142] > One thing to remember is that OSPF costs are calculated > unidirectionally. For example, A's cost to C could be very different from > C's cost to A. In general, IP traffic has to be engineered in both > directions and it for some networks asymmetry in flow might make sense. I > can't think of a reason off hand while watching a hockey game, but > experience has taught me that many odd looking designs are rooted in > rational, informed theory. > > Pete > > > At 04:05 PM 3/4/2002 -0500, Ouellette, Tim wrote: > >I have a question regarding # 2. > > > >let's say both routera and router b are connected and advertising the link > >between them to router c. The connection from routera to routerc is a 64k > >frame circuit. The link betwen routerb and routerc is a 64k ISDN (1 b). If > >routera advertises the network between itself and routerb with a cost of 10, > >and routerb advertises that same network with a cost of 100. All other > >things being equal when routerc gets the two updates, he will prefer to take > >the frame circuit towards routera to get to that network. Why would anyways > >want this? What if the circuit between routerb and routerc was a backup ISDN > >that you had to pay extra for to bring up during normal business hours or > >something like that. I guess it all comes down to what your network is > >doing. Whether two boxes advertise the same cost to a network is really only > >dependent upon which path you want to take to get there. If they both > >advertise the same, you may potentially load balance. If that's not desired, > >crank up the cost of one of those boxes so it's path is less-desirable. > > > >router a --- routerb > > \/ > > \ / > >\/ > >routerc > > > >Was I just rambling? Did that make sense. > > > >Tim > > > > > >-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: > > > > > > > > > > >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 Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=37253&t=37142 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: basic OSPF questions [7:37142]
>One thing to remember is that OSPF costs are calculated >unidirectionally. For example, A's cost to C could be very different from >C's cost to A. In general, IP traffic has to be engineered in both >directions and it for some networks asymmetry in flow might make sense. I >can't think of a reason off hand while watching a hockey game, but >experience has taught me that many odd looking designs are rooted in >rational, informed theory. > >Pete There's a whole class of applications for this sort of thing, and indeed there is a Unidirectional Link Routing group in the IETF for dealing with them. Much of the leading research work is in France, where practical applications deal with using high-bandwidth satellite links in one direction to deliver educational content to Africa, and a low-speed terrestrial return link for acknowledgements. > > >At 04:05 PM 3/4/2002 -0500, Ouellette, Tim wrote: >>I have a question regarding # 2. >> >>let's say both routera and router b are connected and advertising the link >>between them to router c. The connection from routera to routerc is a 64k >>frame circuit. The link betwen routerb and routerc is a 64k ISDN (1 b). If >>routera advertises the network between itself and routerb with a cost of 10, >>and routerb advertises that same network with a cost of 100. All other >>things being equal when routerc gets the two updates, he will prefer to take >>the frame circuit towards routera to get to that network. Why would anyways >>want this? What if the circuit between routerb and routerc was a backup ISDN >>that you had to pay extra for to bring up during normal business hours or >>something like that. I guess it all comes down to what your network is >>doing. Whether two boxes advertise the same cost to a network is really only >>dependent upon which path you want to take to get there. If they both >>advertise the same, you may potentially load balance. If that's not desired, >>crank up the cost of one of those boxes so it's path is less-desirable. >> >>router a --- routerb >> \/ >>\ / >> \/ >> routerc >> >>Was I just rambling? Did that make sense. >> >>Tim >> >> >>-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: >> >> >> >> >> >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 Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=37223&t=37142 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: basic OSPF questions [7:37142]
One thing to remember is that OSPF costs are calculated unidirectionally. For example, A's cost to C could be very different from C's cost to A. In general, IP traffic has to be engineered in both directions and it for some networks asymmetry in flow might make sense. I can't think of a reason off hand while watching a hockey game, but experience has taught me that many odd looking designs are rooted in rational, informed theory. Pete At 04:05 PM 3/4/2002 -0500, Ouellette, Tim wrote: >I have a question regarding # 2. > >let's say both routera and router b are connected and advertising the link >between them to router c. The connection from routera to routerc is a 64k >frame circuit. The link betwen routerb and routerc is a 64k ISDN (1 b). If >routera advertises the network between itself and routerb with a cost of 10, >and routerb advertises that same network with a cost of 100. All other >things being equal when routerc gets the two updates, he will prefer to take >the frame circuit towards routera to get to that network. Why would anyways >want this? What if the circuit between routerb and routerc was a backup ISDN >that you had to pay extra for to bring up during normal business hours or >something like that. I guess it all comes down to what your network is >doing. Whether two boxes advertise the same cost to a network is really only >dependent upon which path you want to take to get there. If they both >advertise the same, you may potentially load balance. If that's not desired, >crank up the cost of one of those boxes so it's path is less-desirable. > >router a --- routerb > \/ > \ / >\/ >routerc > >Was I just rambling? Did that make sense. > >Tim > > >-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: > > > > > >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 Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=37217&t=37142 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: basic OSPF questions [7:37142]
I believe Rc would know the network to be equal cost between the two routers. -- RFC 1149 Compliant. ""Ouellette, Tim"" wrote in message news:[EMAIL PROTECTED].; > I have a question regarding # 2. > > let's say both routera and router b are connected and advertising the link > between them to router c. The connection from routera to routerc is a 64k > frame circuit. The link betwen routerb and routerc is a 64k ISDN (1 b). If > routera advertises the network between itself and routerb with a cost of 10, > and routerb advertises that same network with a cost of 100. All other > things being equal when routerc gets the two updates, he will prefer to take > the frame circuit towards routera to get to that network. Why would anyways > want this? What if the circuit between routerb and routerc was a backup ISDN > that you had to pay extra for to bring up during normal business hours or > something like that. I guess it all comes down to what your network is > doing. Whether two boxes advertise the same cost to a network is really only > dependent upon which path you want to take to get there. If they both > advertise the same, you may potentially load balance. If that's not desired, > crank up the cost of one of those boxes so it's path is less-desirable. > > router a --- routerb > \/ > \ / >\/ >routerc > > Was I just rambling? Did that make sense. > > Tim > > > -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: > > > > > >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 Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=37196&t=37142 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: basic OSPF questions [7:37142]
I have a question regarding # 2. let's say both routera and router b are connected and advertising the link between them to router c. The connection from routera to routerc is a 64k frame circuit. The link betwen routerb and routerc is a 64k ISDN (1 b). If routera advertises the network between itself and routerb with a cost of 10, and routerb advertises that same network with a cost of 100. All other things being equal when routerc gets the two updates, he will prefer to take the frame circuit towards routera to get to that network. Why would anyways want this? What if the circuit between routerb and routerc was a backup ISDN that you had to pay extra for to bring up during normal business hours or something like that. I guess it all comes down to what your network is doing. Whether two boxes advertise the same cost to a network is really only dependent upon which path you want to take to get there. If they both advertise the same, you may potentially load balance. If that's not desired, crank up the cost of one of those boxes so it's path is less-desirable. router a --- routerb \/ \ / \/ routerc Was I just rambling? Did that make sense. Tim -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: >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 Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=37195&t=37142 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: basic OSPF questions [7:37142]
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 0x (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]
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 0x (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=37178&t=37142 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: basic OSPF questions [7:37142]
Someone else has tackled the others, I go after #1): As you probably already know, in a lab setting, loopbacks are great for building up fictional stub networks to be used in reachability testing and summarization/filtering scenarios. For example, you can create interface loopback0 with an ip address of 10.1.1.1/24. By default, in OSPF, this loopback interface's network would be advertised as 10.1.1.1/32 even though you have specified the /24 mask. This makes for some confusion. If you specify on the loopback interface OSPF network type as point-to-point, it will force the /24 advertisement to be made instead of the /32. This makes the loopback interfaces appear to be just another stub network (not to be confused with OSPF stub area). Ryan -Original Message- From: bergenpeak [mailto:[EMAIL PROTECTED]] Sent: Monday, March 04, 2002 9:00 AM To: [EMAIL PROTECTED] Subject: basic OSPF questions [7:37142] 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? 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? 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? 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? 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? 5) Is there a difference between DBD and DDP packets? Thanks Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=37162&t=37142 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: basic OSPF questions [7:37142]
1. Hopefully someone else will tell you the answer to this one as I have no idea what the benefit is. 2. The cost dosen't have to be the same. The router will report it's own calculated cost to the neighbor based on it's cost because it's directly connected to it. So if you have: RA--RB (s0)--(s0) RC (e0)___| If router C considers it's S0 link to be a cost of 2 and Router B considers the same link to be 1000, then RA will receive link to be based on RB's calculation. But router A will receive Router C's e0 link as based on the cost of Rc's calculation of the link. 3. According to RFC 2328, it's the router ID which is used in the master/slave determination. I tested it and it is the Router ID. 4. I believe you are correct in your explanation. 5. I believe they both mean Database Descriptor Packet. -- RFC 1149 Compliant. ""bergenpeak"" wrote in message news:[EMAIL PROTECTED].; > 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? > > 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? > > 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? > > 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? > 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? > > 5) Is there a difference between DBD and DDP packets? > > Thanks Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=37156&t=37142 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
