Cisco vs. Juniper

Some subtle differences Because OSPF has several checks and balances in regards to neighbor adjacencies, and because those adjacencies are essential for actual routing, their defaults remain the same between the two vendors. These include authentication (except in the case of OSPFv3), hello/dead intervals and area types. One note about authentication: in Cisco IOS when area authentication (either MD5 or Simple) is configured at the protocol level it triggers the bit in the AuType field within the header. This means that without a like configuration on neighboring routers, adjacencies will not be created. Juniper does not, at the protocol level, trigger the AuType bit unless the key is configured within the interface.

In the examples below, both configurations will change the AuType to 2 which would satisfy one of the adjacency requirements. Of course if we were trying to get these two to “neighbor-up” it wouldn't work.

Cisco Example

 router ospf 1
 area 0.0.0.0 authentication message-digest
 end

Juniper Example

 protocols ospf {
      area 0.0.0.0 {
           authentication-type md5;
      interface ge1/0/1.0{
           authentication  {  
                md5 1 key juniper;
   }
   } 
   }
 }

Another difference lies within the functions of stub ABRs. This is a classic difference between routers made for enterprise operations and routers made for the provider industry. In Cisco IOS a stub router which is configured to either allow summary route or inject just one summary (totally stubby) will do just that. In Juniper land, that particular function is optional and must be configured using the “default-metric” command.

On broadcast/multi-access media such as Ethernet, OSPF elects a Designated Router (DR) to act as the originator of network advertisements and synchronizing of link-state databases. The election process involves the comparison of OSPF priority values and Router-IDs. On a data link the highest priority wins the election. Each vendor has a default priority and each vendor recognizes that a priority of 0 does not allow that interface to be considered in an election. Cisco has a default priority of 1 and Juniper has a default of 128. This means of course, that if you put Cisco and Juniper on the same broadcast segment, Juniper will by default become the designated router.