Continuing with our OSPF and interior gateway protocols we will not look at an MD5 implementation utilizing OSPF on a Cisco router. We will again continue with our 3 router topology as used in both the EIGRP MD5 example and the OSPF plain text example. There are very few changes that will need to be made to our earlier OSPF example using plain text. The topology is as follows.
The main reason to utilize MD5 authentication on your OSPF instance is to protect the keys being passed across the active interfaces in OSPF. To start this example we will remove the existing ip ospf commands underneath each interface. We will then re-add the modified commands to establish the MD5 connected neighbors.
interface FastEthernet0/0 ip address 192.168.42.2 255.255.255.252 ip ospf authentication message-digest ip ospf message-digest-key 1 md5 OSPFKEY !
By expanding our interface configuration commands to state their message-digest options we are establishing a more secure authentication to our OSPF instance. We still have the existing downside to OSPF authentication in the fact that changing the keys requires the neighbors to temporarily go down. This leaves a change to the OSPF authentication to be initiated during an established downtime.
Full router configurations follows:
! hostname R1 ! interface FastEthernet0/0 ip address 192.168.42.1 255.255.255.252 ip ospf authentication message-digest ip ospf message-digest-key 1 md5 OSPFKEY duplex auto speed auto ! interface FastEthernet1/0 ip address 172.16.42.1 255.255.255.252 ip ospf authentication message-digest ip ospf message-digest-key 1 md5 OSPFKEY duplex auto speed auto ! router ospf 42 router-id 1.1.1.1 network 172.16.42.0 0.0.0.3 area 0 network 192.168.42.0 0.0.0.3 area 0 ! end
! hostname R2 ! interface FastEthernet0/0 ip address 10.0.42.1 255.255.255.252 ip ospf authentication message-digest ip ospf message-digest-key 1 md5 OSPFKEY duplex auto speed auto ! interface FastEthernet1/0 ip address 172.16.42.2 255.255.255.252 ip ospf authentication message-digest ip ospf message-digest-key 1 md5 OSPFKEY duplex auto speed auto ! router ospf 42 router-id 2.2.2.2 network 10.0.42.0 0.0.0.3 area 0 network 172.16.42.0 0.0.0.3 area 0 ! end
! hostname R3 ! interface FastEthernet0/0 ip address 192.168.42.2 255.255.255.252 ip ospf authentication message-digest ip ospf message-digest-key 1 md5 OSPFKEY duplex auto speed auto ! interface FastEthernet1/0 ip address 10.0.42.2 255.255.255.252 ip ospf authentication message-digest ip ospf message-digest-key 1 md5 OSPFKEY duplex auto speed auto ! router ospf 42 router-id 3.3.3.3 network 10.0.42.0 0.0.0.3 area 0 network 192.168.42.0 0.0.0.3 area 0 ! end
