Hi All,
I am hoping someone can help me with this problem because I am stumped.
I have two routers, R1 which is a 2821 and R2 which is a 1841 in a router on a stick configuration.
I am trying to setup OSPF between the routers but both routers are stuck with the neighbor status EXSTART/BDR.
I have done some research on this issue and most of the time this issue is caused by a MTU mismatch on the router interfaces.
I have checked both routers interfaces and they both using an MTU of 1500 bytes and I am not getting any MTU mismatch messages when I do a debug ip ospf adj.
Further to this I have checked for MTU issues with ping x.x.x.x df-bit size 1500 on both routers.
I have narrowed down the issue to a problem with NAT. As soon as I remove "ip nat outside" from GigabitEthernet0/1 on R1 the issue disapears and OSPF neighbor status changes from EXSTART/BDR to FULL/DR
The strangest part about all this is I was using a 2801 previously for R2 and I had no issues at all. I have even tried a few diffrent IOS versions to rule out any IOS bugs.
R1 Config
interface GigabitEthernet0/1
ip address 10.60.133.1 255.255.255.248
no ip redirects
no ip unreachables
no ip proxy-arp
ip nat outside
ip virtual-reassembly in
duplex auto
speed auto
end
interface Vlan1
ip address 10.180.1.254 255.255.255.0
ip nat inside
ip virtual-reassembly in
ip nat inside source route-map INTERNET interface GigabitEthernet0/0 overload
ip nat inside source route-map LAB interface GigabitEthernet0/1 overload
access-list 1 permit 10.0.0.0 0.255.255.255
route-map INTERNET permit 10
match ip address 1
match interface GigabitEthernet0/0
route-map LAB permit 10
match ip address 1
match interface GigabitEthernet0/1
router ospf 1
passive-interface default
no passive-interface GigabitEthernet0/1
no passive-interface Vlan1
network 10.60.133.1 0.0.0.0 area 0
network 10.180.1.254 0.0.0.0 area 0
R2 Config
interface FastEthernet0/1.101
encapsulation dot1Q 101
ip address 10.60.133.6 255.255.255.248
end
router ospf 1
log-adjacency-changes
summary-address 10.48.0.0 255.240.0.0
redistribute bgp 65133 subnets
passive-interface default
no passive-interface FastEthernet0/1.101
network 10.60.133.6 0.0.0.0 area 0
