BGP Configuration with and without another IGP

jskfan
jskfan used Ask the Experts™
on
BGP Configuration with and without another IGP

in the topology below, I would like to know if :

-- BGP needs to be configured on R1  R2,R3,R4  without any other IGP (OSPF)configured on the same routers.
-- Or BGP can be configured only on R1 and R4, but IGP (OSPF) should be configured on all 4 routers R1,R2,R3,R4

Thanks


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Distinguished Expert 2018
Commented:
If you want to  use only BGP you would have to create full mesh .. each router would have 3 BGP peers in topology above.

Having BGP on just edge routers would require state routing protocol (OSPF or ISIS) + MPLS in core, tunnel between R1 and R4, or redistribution of BGP routes into OSPF (typically is not thw way to go if full routing table needs to be redistributed).

Author

Commented:
Ok, Can we have OSPF on R1,R2,R3,R4  and BGP just on the Edges R1 and R4 without using MPLS ?

OR that approach will require redistributing BGP into OSPF ?
Distinguished Expert 2018

Commented:
If BGP is present only on R1 and R4 routes would need to be redistributed into OSPF, otherwise traffic will be black holed or next hop would not be reachable so BGP routes learned from R1 and R4 would not enter routing table.

Author

Commented:
With MPLS + OSPF on all 4 routers; R1,R2,R3,R4  , we do not need to redistribute BGP into OSPF.  Correct ?

Author

Commented:
Thank you Justincase.
I thout it was closed

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