John,
I am having somewhat different results.
I have two routers connected via s1/0 interfaces, the network type configured to NBMA by command. The relevant configuration:
R1:
interface Serial1/0
ip address 10.0.0.1 255.255.255.0
ip ospf network non-broadcast
ip ospf priority 5
ip ospf 1 area 0
router ospf 1
neighbor 10.0.0.2 priority 200
R2:
interface Serial1/0
ip address 10.0.0.2 255.255.255.0
ip ospf network non-broadcast
ip ospf 1 area 0
router ospf 1
neighbor 10.0.0.1 priority 150
According to the priorities set on interface, the R1 should be the DR while R2 should be the BDR. On the other hand, according to the priorities set in the
neighbor
commands, the R2 should be DR while R1 is the BDR.
When s1/0 interfaces on both routers are shut down, the
show ip ospf nei
gives this output:
R1(config-if)#do show ip ospf n
Neighbor ID Pri State Dead Time Address Interface
N/A 200 ATTEMPT/DROTHER - 10.0.0.2 Serial1/0
R2(config-if)#do show ip ospf n
Neighbor ID Pri State Dead Time Address Interface
N/A 150 ATTEMPT/DROTHER - 10.0.0.1 Serial1/0
The priorities displayed here are taken from the
neighbor
command. However, after the interfaces are brought up and the state is 2WAY, the priorities immediately change back to their values as set on the interfaces:
R1(config-if)#do show ip ospf n
Neighbor ID Pri State Dead Time Address Interface
10.0.0.2 1 2WAY/DROTHER 00:01:54 10.0.0.2 Serial1/0
R2(config-if)#do show ip ospf n
Neighbor ID Pri State Dead Time Address Interface
10.0.0.1 5 2WAY/DROTHER 00:01:50 10.0.0.1 Serial1/0
Note that as soon as the two routers hear and accept each other's Hello packets, the priorities revert to their real values as configured on the interfaces. After the wait period expires, the DR/BDR elections will go by the real priorities, resulting in R1 being the DR and R2 being the BDR, according to the priorities set up on interfaces:
R1(config-if)#do show ip ospf n
Neighbor ID Pri State Dead Time Address Interface
10.0.0.2 1 FULL/BDR 00:01:58 10.0.0.2 Serial1/0
R2(config-if)#do show ip ospf n
Neighbor ID Pri State Dead Time Address Interface
10.0.0.1 5 FULL/DR 00:01:46 10.0.0.1 Serial1/0
From this it follows for me that the priority configured in the
neighbor
command has an effect only until we receive a Hello packet from that neighbor. As soon as we receive and accept a neighbor's Hello packet, we will use its real priority instead of the one defined in the
neighbor
command.
There is an interesting issue: if more
neighbors
are defined, some having a non-zero priority and another having unspecified priority, the router seems to send Hello packets initially only to routers that are preconfigured with non-zero priority. Only after the DR and BDR are elected, the router starts to send Hellos to all neighbors including those with the priority preconfigured to 0:
R1(config-if)#do show run | sec router ospf 1
router ospf 1
log-adjacency-changes detail
neighbor 10.0.0.3 priority 255
neighbor 10.0.0.2
neighbor 10.0.0.4 priority 90
R1(config-if)#do show ip ospf n
Neighbor ID Pri State Dead Time Address Interface
N/A 255 DOWN/DROTHER - 10.0.0.3 Serial1/0
N/A 0 DOWN/DROTHER - 10.0.0.2 Serial1/0
N/A 90 DOWN/DROTHER - 10.0.0.4 Serial1/0
Continuation follows...
