[c-nsp] Newbish OSPF DR question on VLANs

[Rodney Dunn]

That does not look right.

Can you get 'debug ip os adj' and flap the vlan 50
on either A or C?

Before you do it get: sh ip os int vlan 50 on both

Rodney

On Thu, Jun 07, 2007 at 12:57:39PM +0300, Hank Nussbacher wrote:
> At 05:00 AM 07-06-07 -0400, Rodney Dunn wrote:
> >Also depends if you have the priority set and who came up first.
> 
> From the OSPF Design Guide:
> http://www.cisco.com/warp/customer/104/1.html
> 
> "DR and BDR election is done via the Hello protocol. Hello packets are
> exchanged via IP multicast packets (Appendix B) on each segment. The
> router with the highest OSPF priority on a segment will become the DR
> for that segment. The same process is repeated for the BDR. In case of a
> tie, the router with the highest RID will win. The default for the
> interface OSPF priority is one. Remember that the DR and BDR concepts
> are per multiaccess segment. Setting the ospf priority on an interface
> is done using the ip ospf priority <value> interface command."
> 
> No priority is set.
> 
> So how is it that on router A:
> A#sho ip ospf nei
> 
> Neighbor ID     Pri   State           Dead Time   Address         Interface
> 192.168.1.4       1   FULL/DR         00:00:35    10.1.3.2        Vlan50
> 192.168.1.2       1   FULL/DR         00:00:37    10.1.1.2        Vlan20
> 
> sees 192.168.1.4 as DR and on router C:
> C#sho ip ospf nei
> 
> Neighbor ID     Pri   State           Dead Time   Address         Interface
> 192.168.1.1       1   FULL/DR         00:00:37    10.1.3.1        Vlan50
> 192.168.1.3       1   FULL/DR         00:00:38    10.3.3.1        Vlan40
> 192.168.1.2       1   FULL/DR         00:00:30    10.2.2.2        Vlan30
> 
> on the same VLAN50 it sees 192.168.1.1 as DR?
> 
> See http://www.interall.co.il/vlans.png for simple network schematic.
> 
> There is something I am missing here that I am trying to understand.
> 
> Thanks,
> Hank
> 
> 
> 
> >What is the uptime of C?
> >
> >On Thu, Jun 07, 2007 at 11:48:52AM +0300, Hank Nussbacher wrote:
> >> What causes a router to become a Designated Router (DR) on a VLAN?  I
> >> always thought highest router-id, but I have a few test routers and 
> >here is
> >> what I get:
> >>
> >> C#sho ip ospf nei
> >>
> >> Neighbor ID     Pri   State           Dead Time   Address         
> >Interface
> >> 192.168.1.1       1   FULL/DR         00:00:37    10.1.3.1        Vlan50
> >> 192.168.1.3       1   FULL/DR         00:00:38    10.3.3.1        Vlan40
> >> 192.168.1.2       1   FULL/DR         00:00:30    10.2.2.2        Vlan30
> >> C#sho ip ospf neigh 192.168.1.1 ?
> >> C#sho ip ospf neigh 192.168.1.1 deta
> >>  Neighbor 192.168.1.1, interface address 10.1.3.1
> >>     In the area 0 via interface Vlan50
> >>     Neighbor priority is 1, State is FULL, 6 state changes
> >>     DR is 10.1.3.1 BDR is 10.1.3.2
> >>     Options is 0x52
> >>     LLS Options is 0x1 (LR)
> >>     Dead timer due in 00:00:34
> >>     Neighbor is up for 00:27:35
> >>     Index 1/1, retransmission queue length 0, number of retransmission 1
> >>     First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0)
> >>     Last retransmission scan length is 1, maximum is 1
> >>     Last retransmission scan time is 0 msec, maximum is 0 msec
> >> C#sho ip ospf neigh 192.168.1.2 deta
> >>  Neighbor 192.168.1.2, interface address 10.2.2.2
> >>     In the area 0 via interface Vlan30
> >>     Neighbor priority is 1, State is FULL, 6 state changes
> >>     DR is 10.2.2.2 BDR is 10.2.2.1
> >>     Options is 0x52
> >>     LLS Options is 0x1 (LR)
> >>     Dead timer due in 00:00:31
> >>     Neighbor is up for 00:27:49
> >>     Index 3/3, retransmission queue length 0, number of retransmission 0
> >>     First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0)
> >>     Last retransmission scan length is 0, maximum is 0
> >>     Last retransmission scan time is 0 msec, maximum is 0 msec
> >> C#sho ip ospf neigh 192.168.1.3 deta
> >>  Neighbor 192.168.1.3, interface address 10.3.3.1
> >>     In the area 0 via interface Vlan40
> >>     Neighbor priority is 1, State is FULL, 6 state changes
> >>     DR is 10.3.3.1 BDR is 10.3.3.2
> >>     Options is 0x52
> >>     LLS Options is 0x1 (LR)
> >>     Dead timer due in 00:00:37
> >>     Neighbor is up for 00:28:02
> >>     Index 2/2, retransmission queue length 0, number of retransmission 1
> >>     First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0)
> >>     Last retransmission scan length is 1, maximum is 1
> >>     Last retransmission scan time is 0 msec, maximum is 0 msec
> >>
> >> IOS 12.3(11)T2 if it makes a difference.
> >>
> >> All four of them become DR.  I have attached a png file that I hope makes
> >> it thru the Mailman filter.
> >>
> >> Thanks,
> >> -Hank
> >
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