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OSPF Configuration - A sample template on multi-vendor routers

OSPF Configuration - A sample template on multi-vendor routers

There are commons and differences to the time when it comes to configuring an OSPF routing protocol on a router you manage, based on the router's manufacturer. We will take a look at the basic sample of configuring OSPF on Cisco IOS-XE and Juniper's JunOS operation systems.


OSPF on Cisco IOS-XE

With ios-xe we start configuring OSPF by mentioning the numerical value of the:


OSPF Process ID

And what that does mean is just a number to isolate some hierarchical designs of the OSPF process on the router of cisco. Does it have to be matched on both the peering ends?, the answer is NO Does it affect some priorities in some OSPF election processes?, the answer is also NO Is it that mandatory?, well based on that "OS" it is, but it is not a general OSPF concept? As it is missing with the other vendors!! That makes the first line of configuration look like this:        

OERouter1(config)#router OSPF [Process ID] i.e. "OERouter1(config)#router ospf 10

OSPF Network Advertisement

The later step after getting into the hierarchical mode of OSPF, specifying the process ID as well, is to advertise the networks. These networks prefixes and prefix lengths will be announced to the adjacent neighbors inside the transported LSA's of the OSPF routing protocol. OERouter1(config-router)#network [network prefix] [network wild card mask] _____ i.e. "OERouter1(config-router)#network 10.10.10.0 0.0.0.255 _____ and that will be advertising a network with the prefix of 10.10.10.0 and the prefix length of 24


OSPF Area ID

The real key here in OSPF configuration is the Area ID, the Area ID does the isolation, it does the creation of multiple databases LSDB, it generates the need and the role for the ABR Router, It has to be matched on both the ends of the peering OSPF routers, and there will be a database for every area. OERouter1(config-router)#network [network prefix] [network wild card mask] Area [Area ID] i.e. "OERouter(1config-router)#network 10.10.10.0 0.0.0.255 Area 0 That line had just advertised the network of 10.10.10.0/24 into the domain and database of Area 0 Any other participating router within the same area will receive some LSA's carrying the 10.10.10.0/24 network advertisement.


OSPF on JunOS OS

On the other end, the other router awaiting to peer with the Cisco IOS-XE router will be a router from Juniper Networks, Having the one unified intelligent JunOS OS installed on, Here, just like it is with many other vendors, there will be no "Process ID" Advertise a network and its Area ID under the umbrella of OSPF configuration hierarchy, and that is it. [edit] OEUser@R2#edit protocols [dynamic routing protocol] OEUser@R2#edit area [Area ID] i.e. OEUser@R2#edit protocols OSPF OEUser@R2#edit area 0.0.0.0 Areas with JunOS can be mentioned either as a normal numerical value [0] or as a 32-bit value [0.0.0.0] The classic of JunOS is to use the [0.0.0.0] form. After specifying the Area ID, and also making sure that the syntax started with "edit" We will log in another JunOS hierarchical mode, where we can advertise "Participating Interfaces" instead of "Networks" OEUser@R2#set interfaces [interface_ID.logical_unit] i.e OEUser@R2#set interfaces ge-0/0/0.0 or: OEUser@R2#set interfaces ge-0/0/0 unit 0 Now any network getting advertised within the interface ge-0/0/0 generally (unit 0) Will be advertised out of that interface as a network participating in OSPF Area 0, to the other side.


Point of Argument

Will the above samples of configuring 2 different platforms, running 2 different operating systems, Having 2 different ways of advertising a network out, and also one of them misses a mandatory statement based on the other aspect, Will all of that work!!! The answer is YES, OSPF is an open standard protocol, it is supported across multiple vendors, the slight differences in configuration samples are just some languages differentiations, But neighboring adjacency will come up and full Link-State Databases (LSDB's) will be established and fully synchronized between the routers using LSA's.


A more unified method

As we've seen earlier, with Cisco IOS-XE, the OSPF configuration was done by advertising a network, while in JunOS it was done by advertising an interface. That can have an alternative way on Cisco's IOS-XE, by also advertising an interface, BUT, from the interface hierarchical config. mode. OERouter1(config)#interface [interface ID] OERouter1(config-if)#ip ospf [Process ID] Area [Area ID] i.e. OERouter1(config)#interface gi 0/1 OERouter1(config-if)#ip ospf 10 area 0

Author:

Orhan Ergun
Orhan Ergun Orhan Ergun, CCIE/CCDE Trainer, Author of Many Networking Books, Network Design Advisor, and Cisco Champion 2019/2020/2021

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Wrote many books, mostly on Network Design, joined many IETF RFCs, gave Public talks at many Forums, and mentored thousands of his students.  

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