Connect two Backbone area via IS-IS

[Tariqemad]

Hi all ,, I have (4) Edge router .. The Network routing between ( R1 --> R3  ) OSPF on Backbone Area (i.e Area 0 ) and the Network routing between ( R4 --> R2  ) OSPF on Backbone Area (i.e Area 0 ) , Also the Network routing between ( R1 --> R2  ) IS-IS ..  My goal to connect the ( Area 0 for R3  with Area 0 for R2 ) through IS-IS Network .. Is this possible .. and if yes how we can do this .. 

below in the attachment you will fine my idea topology ,, Thanks in advance 

[Moaz.Elzhrawey]

Hi,

Good question,

Unfortunately, you can't.

But, there is a workaround to have the partitioned Area 0 get connected, which by doing the following: 

1- Create Interface Loopback on R1 and R2, then advertise them in OSPF

2- Enable OSPF to IS-IS and IS-IS redistribution (Mutual redistribution) on R1 and R2.

By doing so, you would have Loopback reachability on both R1 and R2

3- Create GRE tunnel interface on both R1 and R2 using those loopbacks created in step 1 as a source-interface.

4- Assign those tunnel interfaces to OSPF area 0.

So, finally you will have full OSPF running on top of IS-IS which will be considered as an Underlay (just a carrier) and the OSPF area 0 will be the Overlay.

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