Re: OSPF DR and BDR elections [7:73504]
At 8:08 PM + 8/6/03, Marko Milivojevic wrote: I wonder what the logic for that is. I wonder, too. :) The reason could be as simple as the possibility to reuse the code (or function-call). For that brief moment when there is BDR, but no DR, exactly the same code base can be used as if router has realized that DR just failed miserably :-). I just realized that my logic above actually makes sense. Of course, someone will correct me if I'm horribly wrong. That's the exact reason it's done that way. I think it's documented in the code in Moy's second book on implementation, but it might be the first. Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=73636t=73504 -- **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
RE: OSPF DR and BDR elections [7:73504]
The DR is not chosen from the remaining list. The DR is chosen from the list of routers that declared themselves designated routers (this is why a high-priority router that comes up late won't take over the DR role from an existing DR), or if no router declared itself DR, then the BDR will become DR (this is why a high-priority router that came up late won't necessarily become DR even if the existing DR dies). See RFC2328, Page 75 for more details. Thanks, Zsombor DeVoe, Charles (PKI) wrote: I am reading the CCNP/CCIP BSCI Study Guide by Todd Lammle from Sybex. In the OSPF section under the discussion of DR and BDR (page 171) he says that the BDR is chosen first and that the DR is chosen from the reaming list. That seems illogical and backwards. Can someone please confirm or deny and explain it. Thanks Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=73524t=73504 -- **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
Re: OSPF DR and BDR elections [7:73504]
The OSPF interface priority is the parameter that controls DR election. Its default value is 1. When OSPF interface priority is 0, the router is not eligible to become a DR. If a router comes up on a network segment and there are no other routers there already, it will become a DR. If there is an existing DR (or BDR), the new router will NOT attempt to preempt them. If several routers come up at roughly the same time (or the DR fails), a new DR election process will be triggered. The router with the highest priority value then will become a DR. In short, the DR/BDR election process is not deterministic and depends on the sequence of events. Therefore it is important to be able to prevent routers from EVER becoming DR/BDR, when that is appropriate for the topology in which they are connected. This si accomplished by setting their OSPF interface priority to 0: ospf set interface priority 0 So there has to be a DR first and after that there will be an BDR If you start an router on itsself not yet connected to the network it will start as an BDR. Quoting DeVoe, Charles (PKI) : I am reading the CCNP/CCIP BSCI Study Guide by Todd Lammle from Sybex. In the OSPF section under the discussion of DR and BDR (page 171) he says that the BDR is chosen first and that the DR is chosen from the reaming list. That seems illogical and backwards. Can someone please confirm or deny and explain it. Thanks **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Iwan Hoogendoorn Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=73510t=73504 -- **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
RE: OSPF DR and BDR elections [7:73504]
That is the point I needed clarification on. Just seemed odd that the DR would not be established first, followed by the BDR. For a brief moment when the routers are first started, there is no DR, but there is a BDR. I wonder what the logic for that is. -Original Message- From: Zsombor Papp [mailto:[EMAIL PROTECTED] Sent: Tuesday, August 05, 2003 8:20 PM To: [EMAIL PROTECTED] Subject: RE: OSPF DR and BDR elections [7:73504] Technically, the BDR is elected first. If no router is claiming to be a DR, then the BDR will be immediately promoted to DR. Nonetheless, the end result is pretty much what the web page referenced below describes. Thanks, Zsombor mccloud mike wrote: The DR is elected first by highest priority, the tie breaker is highest RID. Then the process is repeated for the BDR. http://www.cisco.com/warp/customer/104/2.html#10.1 My understanding is that if the DR goes down then the BDR is promoted to DR and an election is held for the new BDR. This means that when the original DR comes back up it can not become DR until both of the current DR and BDR go offline. Cheers, Mike DeVoe, Charles (PKI) wrote: If I am understanding this correctly. There are no routers up in the network. I turn on 3 routers simultaneously at the same time. The routers will first select the BDR. They will then look for the DR. Since none exist, the BDR will be promoted to DR. Then another election will be held to find a new BDR. Is this correct? -Original Message- From: Zsombor Papp [mailto:[EMAIL PROTECTED] Sent: Tuesday, August 05, 2003 11:01 AM To: [EMAIL PROTECTED] Subject: RE: OSPF DR and BDR elections [7:73504] The DR is not chosen from the remaining list. The DR is chosen from the list of routers that declared themselves designated routers (this is why a high-priority router that comes up late won't take over the DR role from an existing DR), or if no router declared itself DR, then the BDR will become DR (this is why a high-priority router that came up late won't necessarily become DR even if the existing DR dies). See RFC2328, Page 75 for more details. Thanks, Zsombor DeVoe, Charles (PKI) wrote: I am reading the CCNP/CCIP BSCI Study Guide by Todd Lammle from Sybex. In the OSPF section under the discussion of DR and BDR (page 171) he says that the BDR is chosen first and that the DR is chosen from the reaming list. That seems illogical and backwards. Can someone please confirm or deny and explain it. Thanks **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=73597t=73504 -- **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
RE: OSPF DR and BDR elections [7:73504]
It may be stated that way in the RFC, I have not checked, but the logic of it is il, as in illogical. ;-) Fred Reimer - CCNA Eclipsys Corporation, 200 Ashford Center North, Atlanta, GA 30338 Phone: 404-847-5177 Cell: 770-490-3071 Pager: 888-260-2050 NOTICE; This email contains confidential or proprietary information which may be legally privileged. It is intended only for the named recipient(s). If an addressing or transmission error has misdirected the email, please notify the author by replying to this message. If you are not the named recipient, you are not authorized to use, disclose, distribute, copy, print or rely on this email, and should immediately delete it from your computer. -Original Message- From: DeVoe, Charles (PKI) [mailto:[EMAIL PROTECTED] Sent: Wednesday, August 06, 2003 7:34 AM To: [EMAIL PROTECTED] Subject: RE: OSPF DR and BDR elections [7:73504] That is the point I needed clarification on. Just seemed odd that the DR would not be established first, followed by the BDR. For a brief moment when the routers are first started, there is no DR, but there is a BDR. I wonder what the logic for that is. -Original Message- From: Zsombor Papp [mailto:[EMAIL PROTECTED] Sent: Tuesday, August 05, 2003 8:20 PM To: [EMAIL PROTECTED] Subject: RE: OSPF DR and BDR elections [7:73504] Technically, the BDR is elected first. If no router is claiming to be a DR, then the BDR will be immediately promoted to DR. Nonetheless, the end result is pretty much what the web page referenced below describes. Thanks, Zsombor mccloud mike wrote: The DR is elected first by highest priority, the tie breaker is highest RID. Then the process is repeated for the BDR. http://www.cisco.com/warp/customer/104/2.html#10.1 My understanding is that if the DR goes down then the BDR is promoted to DR and an election is held for the new BDR. This means that when the original DR comes back up it can not become DR until both of the current DR and BDR go offline. Cheers, Mike DeVoe, Charles (PKI) wrote: If I am understanding this correctly. There are no routers up in the network. I turn on 3 routers simultaneously at the same time. The routers will first select the BDR. They will then look for the DR. Since none exist, the BDR will be promoted to DR. Then another election will be held to find a new BDR. Is this correct? -Original Message- From: Zsombor Papp [mailto:[EMAIL PROTECTED] Sent: Tuesday, August 05, 2003 11:01 AM To: [EMAIL PROTECTED] Subject: RE: OSPF DR and BDR elections [7:73504] The DR is not chosen from the remaining list. The DR is chosen from the list of routers that declared themselves designated routers (this is why a high-priority router that comes up late won't take over the DR role from an existing DR), or if no router declared itself DR, then the BDR will become DR (this is why a high-priority router that came up late won't necessarily become DR even if the existing DR dies). See RFC2328, Page 75 for more details. Thanks, Zsombor DeVoe, Charles (PKI) wrote: I am reading the CCNP/CCIP BSCI Study Guide by Todd Lammle from Sybex. In the OSPF section under the discussion of DR and BDR (page 171) he says that the BDR is chosen first and that the DR is chosen from the reaming list. That seems illogical and backwards. Can someone please confirm or deny and explain it. Thanks **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=73602t=73504 -- **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
Re: OSPF DR and BDR elections [7:73504]
I wonder what the logic for that is. I wonder, too. :) The reason could be as simple as the possibility to reuse the code (or function-call). For that brief moment when there is BDR, but no DR, exactly the same code base can be used as if router has realized that DR just failed miserably :-). I just realized that my logic above actually makes sense. Of course, someone will correct me if I'm horribly wrong. Marko. Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=73628t=73504 -- **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
RE: OSPF DR and BDR elections [7:73504]
If I am understanding this correctly. There are no routers up in the network. I turn on 3 routers simultaneously at the same time. The routers will first select the BDR. They will then look for the DR. Since none exist, the BDR will be promoted to DR. Then another election will be held to find a new BDR. Is this correct? -Original Message- From: Zsombor Papp [mailto:[EMAIL PROTECTED] Sent: Tuesday, August 05, 2003 11:01 AM To: [EMAIL PROTECTED] Subject: RE: OSPF DR and BDR elections [7:73504] The DR is not chosen from the remaining list. The DR is chosen from the list of routers that declared themselves designated routers (this is why a high-priority router that comes up late won't take over the DR role from an existing DR), or if no router declared itself DR, then the BDR will become DR (this is why a high-priority router that came up late won't necessarily become DR even if the existing DR dies). See RFC2328, Page 75 for more details. Thanks, Zsombor DeVoe, Charles (PKI) wrote: I am reading the CCNP/CCIP BSCI Study Guide by Todd Lammle from Sybex. In the OSPF section under the discussion of DR and BDR (page 171) he says that the BDR is chosen first and that the DR is chosen from the reaming list. That seems illogical and backwards. Can someone please confirm or deny and explain it. Thanks **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=73557t=73504 -- **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
RE: OSPF DR and BDR elections [7:73504]
I wonder what the logic for that is. I wonder, too. :) Without answering your question, I would like to point out though that the moment for which there is BDR but no DR is *really* brief. The election process is not something that the routers need to discuss among themselves; every router elects the DR/BDR independently. This is a point that folks miss sometimes. So if there is no DR, then the router that eventually becomes the DR will know *immediately* that it needs to be the DR, because the DR selection is just a function call away from the BDR selection. It's not like the routers have a chit-chat to discuss who will be the BDR, and then they have a rest, and subsequently they discuss who will be the DR... :) In other words, there is no OSPF information exchange between the routers during the process described on Page 75 in RFC2328. Another slightly related thing is that, in the scenario you described below, ie. when all the routers on the same segment are booting up at the same time, then for a relatively long time (ie. the Dead interval) all of them will go into a Waiting state so there won't be any election process for long-long seconds to start with. Compared to this, I guess it is pretty insignificant whether the election process selects the DR a few microseconds sooner or later. Thanks, Zsombor DeVoe, Charles (PKI) wrote: That is the point I needed clarification on. Just seemed odd that the DR would not be established first, followed by the BDR. For a brief moment when the routers are first started, there is no DR, but there is a BDR. I wonder what the logic for that is. -Original Message- From: Zsombor Papp [mailto:[EMAIL PROTECTED] Sent: Tuesday, August 05, 2003 8:20 PM To: [EMAIL PROTECTED] Subject: RE: OSPF DR and BDR elections [7:73504] Technically, the BDR is elected first. If no router is claiming to be a DR, then the BDR will be immediately promoted to DR. Nonetheless, the end result is pretty much what the web page referenced below describes. Thanks, Zsombor mccloud mike wrote: The DR is elected first by highest priority, the tie breaker is highest RID. Then the process is repeated for the BDR. http://www.cisco.com/warp/customer/104/2.html#10.1 My understanding is that if the DR goes down then the BDR is promoted to DR and an election is held for the new BDR. This means that when the original DR comes back up it can not become DR until both of the current DR and BDR go offline. Cheers, Mike DeVoe, Charles (PKI) wrote: If I am understanding this correctly. There are no routers up in the network. I turn on 3 routers simultaneously at the same time. The routers will first select the BDR. They will then look for the DR. Since none exist, the BDR will be promoted to DR. Then another election will be held to find a new BDR. Is this correct? -Original Message- From: Zsombor Papp [mailto:[EMAIL PROTECTED] Sent: Tuesday, August 05, 2003 11:01 AM To: [EMAIL PROTECTED] Subject: RE: OSPF DR and BDR elections [7:73504] The DR is not chosen from the remaining list. The DR is chosen from the list of routers that declared themselves designated routers (this is why a high-priority router that comes up late won't take over the DR role from an existing DR), or if no router declared itself DR, then the BDR will become DR (this is why a high-priority router that came up late won't necessarily become DR even if the existing DR dies). See RFC2328, Page 75 for more details. Thanks, Zsombor DeVoe, Charles (PKI) wrote: I am reading the CCNP/CCIP BSCI Study Guide by Todd Lammle from Sybex. In the OSPF section under the discussion of DR and BDR (page 171) he says that the BDR is chosen first and that the DR is chosen from the reaming list. That seems illogical and backwards. Can someone please confirm or deny and explain it. Thanks **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=73615t=73504 -- **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
RE: OSPF DR and BDR elections [7:73504]
Technically, the BDR is elected first. If no router is claiming to be a DR, then the BDR will be immediately promoted to DR. Nonetheless, the end result is pretty much what the web page referenced below describes. Thanks, Zsombor mccloud mike wrote: The DR is elected first by highest priority, the tie breaker is highest RID. Then the process is repeated for the BDR. http://www.cisco.com/warp/customer/104/2.html#10.1 My understanding is that if the DR goes down then the BDR is promoted to DR and an election is held for the new BDR. This means that when the original DR comes back up it can not become DR until both of the current DR and BDR go offline. Cheers, Mike DeVoe, Charles (PKI) wrote: If I am understanding this correctly. There are no routers up in the network. I turn on 3 routers simultaneously at the same time. The routers will first select the BDR. They will then look for the DR. Since none exist, the BDR will be promoted to DR. Then another election will be held to find a new BDR. Is this correct? -Original Message- From: Zsombor Papp [mailto:[EMAIL PROTECTED] Sent: Tuesday, August 05, 2003 11:01 AM To: [EMAIL PROTECTED] Subject: RE: OSPF DR and BDR elections [7:73504] The DR is not chosen from the remaining list. The DR is chosen from the list of routers that declared themselves designated routers (this is why a high-priority router that comes up late won't take over the DR role from an existing DR), or if no router declared itself DR, then the BDR will become DR (this is why a high-priority router that came up late won't necessarily become DR even if the existing DR dies). See RFC2328, Page 75 for more details. Thanks, Zsombor DeVoe, Charles (PKI) wrote: I am reading the CCNP/CCIP BSCI Study Guide by Todd Lammle from Sybex. In the OSPF section under the discussion of DR and BDR (page 171) he says that the BDR is chosen first and that the DR is chosen from the reaming list. That seems illogical and backwards. Can someone please confirm or deny and explain it. Thanks **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=73575t=73504 -- **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
OSPF DR and BDR elections [7:73504]
I am reading the CCNP/CCIP BSCI Study Guide by Todd Lammle from Sybex. In the OSPF section under the discussion of DR and BDR (page 171) he says that the BDR is chosen first and that the DR is chosen from the reaming list. That seems illogical and backwards. Can someone please confirm or deny and explain it. Thanks Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=73504t=73504 -- **Please support GroupStudy by purchasing from the GroupStudy Store: http://shop.groupstudy.com FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html
