I tried this in GNS3 and noticed a couple of things.
- The common router seemed to want to require a router-id for ospf. (don't think this is the issue though)
- check the vlans. Typically the port between the common router and the switch would be a trunk and the port from the switch to the voice should be on vlan 2. At least that's my thoughts.
I don't believe it to be the subnet mask so much because a /30 would fit .1 and .2 within it.
I'm going to lab this on my routers to see what I get.
It is the subnet mask as others have stated above. Here's my debug:
R2voice#debug ip ospf hello
OSPF hello debugging is on
Jan 2 13:05:50.311: OSPF-1 HELLO Fa0/0: Send hello to 184.108.40.206 area 0 from 192.0.2.2
Jan 2 13:05:53.271: OSPF-1 HELLO Fa0/0: Rcv hello from 255.255.255.240 area 0 192.0.2.1
Jan 2 13:05:53.271: OSPF-1 HELLO Fa0/0: Mismatched hello parameters from 192.0.2.1
Jan 2 13:05:53.271: OSPF-1 HELLO Fa0/0: Dead R 40 C 40, Hello R 10 C 10 Mask R 255.255.255.0 C 255.255.255.252
I'm thinking that the R=Received and the C=connected(or configured locally) so the received mask is different than the connected/configured and so is causing a mismatched hello error. It is not going to form an adjacency.
If you have the official cert guide on page 274 under ospf fundamentals
subnet mask must match.
mismatch in subnet mask is the problem, HELLO packet that is used to form adjacency contains the below and they have to match
- Router ID of the origination router
- Area ID of the originating router
- IP address and subnet mask of the origination interface
- Authentication type and its information of originating interface
- HELLO interval of originating interface
- Router Dead Interval of originating interface
- Router Priority
- DR and BDR
- 5 flag bits about capability
- Router IDs of originating router's neighbors