> 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=7&i=73615&t=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
