How to Configure OSPF Plain Text Authentication

All routing protocols can be protected by using authentication and OSPF is no exception. There are two options for authentication:

• Plain text authentication
• MD5 authentication

Each OSPF packet will be authenticated if you enable any form of authentication. In this lesson we’ll take a look at how to configure plain text authentication for OSPF. Here’s the topology that we’ll use:

Above you see the topology I’m going to use for authentication. Just two routers but we can use it to check all different methods of authentication.

R1(config)#router ospf 1
R1(config-router)#network 192.168.12.0 0.0.0.255 area 0

R2(config)#router ospf 1
R2(config-router)#network 192.168.12.0 0.0.0.255 area 0

First I’ll enable OSPF, nothing fancy here.

R1(config)#interface fastEthernet 0/0
R1(config-if)#ip ospf authentication
R1(config-if)#ip ospf authentication-key MYPASS

R2(config)#interface fastEthernet 0/0
R2(config-if)#ip ospf authentication
R2(config-if)#ip ospf authentication-key MYPASS

By using the ip ospf authentication command we enable plain text authentication on the interface level. I configured the password MYPASS by using the ip ospf authentication-key command.

R1(config)#router ospf 1
R1(config-router)#area 0 authentication

If you have a lot of interfaces you probably don’t want to enable OSPF authentication for each interface. You can also enable area-wide authentication by using the area authentication command. In my example above I enabled authentication for area 0.

R1#show ip ospf interface fastEthernet 0/0
FastEthernet0/0 is up, line protocol is up 
  Internet Address 192.168.12.1/24, Area 0 
  Process ID 1, Router ID 192.168.12.1, Network Type BROADCAST, Cost: 1
  Transmit Delay is 1 sec, State BDR, Priority 1 
  Designated Router (ID) 192.168.12.2, Interface address 192.168.12.2
  Backup Designated router (ID) 192.168.12.1, Interface address 192.168.12.1
  Flush timer for old DR LSA due in 00:01:49
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    oob-resync timeout 40
    Hello due in 00:00:01
  Supports Link-local Signaling (LLS)
  Index 1/1, flood queue length 0
  Next 0x0(0)/0x0(0)
  Last flood scan length is 1, maximum is 1
  Last flood scan time is 0 msec, maximum is 0 msec
  Neighbor Count is 1, Adjacent neighbor count is 1 
    Adjacent with neighbor 192.168.12.2  (Designated Router)
  Suppress hello for 0 neighbor(s)
  Simple password authentication enabled

If you use the show ip ospf interface command you can see OSPF information per interface. You can also check if authentication is enabled. You can see the neighbor count is 1 and simple password authentication is enabled.

R1#debug ip ospf packet 
OSPF packet debugging is on

OSPF: rcv. v:2 t:1 l:48 rid:192.168.12.2
      aid:0.0.0.0 chk:B9F0 aut:1 auk: from FastEthernet0/0

I love debugs…when it comes to Cisco not Google but debug is your friend. It gives you so much information. If you use debug ip ospf packet you can see that authentication is enabled. In my example I receive a packet and it says aut:1 which means that plain text authentication is enabled.

• Aut:0 is no authentication.
• Aut:1 is plain text authentication.
• Aut:2 is MD5 authentication.

hostname R1
!
interface FastEthernet0/0
 ip address 192.168.12.1 255.255.255.0
 ip ospf authentication
 ip ospf authentication-key MYPASS
!
router ospf 1
 network 192.168.12.0 0.0.0.255 area 0
 area 0 authentication
!
end

hostname R2
!
interface FastEthernet0/0
 ip address 192.168.12.2 255.255.255.0
 ip ospf authentication
 ip ospf authentication-key MYPASS
!
router ospf 1
 network 192.168.12.0 0.0.0.255 area 0
 area 0 authentication
!
end

That’s all for now. In the next lesson we’ll look at MD5 authentication. If you enjoyed this lesson please leave a comment!