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
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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Thanks for your replay ,, but i will face problems here
1- the MTU issue ( the GRE accept not more 1500 )
2- heavy traffic ( the traffic may be exceeded 100G )
3- If i have connection between ( R3 & R4 ) on Area 0 ( here i will face problem between the interior and exterior routing ) So all the traffic will go through the interior routing because i will have redistribute from the ISIS side ,, Is i'm Right ..
So , Any advice to solve these problems .. Thanks in advance ..
1- MTU wouldn't your biggest problem, becz the overhead is affordable unless you having a critical apps which considering the fragmentation is the first enemy.
2- if you have such amount of traffic, this means you're not running ISR routers, ASR at minimum, if so, drop the GRE tunnel option and go with VXLAN.
3- to deal with the issue of using interior or redist routes, you can use filtering easily and rely only on one of routes either the local or redist.
Regarding choosing the IS-IS routes over the redist routers, so you can use the following commands to change the AD of the redist routes to whatever you need to prefer IS-IS over External, or the opoosit,
Router(config)#router ospf 1
Starts the OSPF routing process
Router(config-router)#distance ospf intra-area 105 inter-area 105 external 125
Changes the AD to 105 for intra-area and interarea routes, and changes the AD to 125 for external routes