06-04-2010 11:49 AM - edited 03-04-2019 08:41 AM
This is a question of how IBGP operates with OSPF.
Firslty, synchronization has been disabled.
My understanding is that IBGP will check its BGP table for best next-hop to its intended destination. Then after that best next-hop is determined, BGP will then tell OSPF here is my best next hop. Get me there! Thats when the recursive routing now takes place. Is this correct?
Please no guess work. Answer, only if you are sure. Thanks,
Solved! Go to Solution.
06-04-2010 01:51 PM
Hello,
yes, your understanding or recursion is correct
Hope to help
Giuseppe
06-04-2010 12:06 PM
Hello west33637,
so it is in provider networks for successful forwarding one of the following conditions has to be met:
a) or iBGP is enabled everywhere using route reflector servers and/or BGP confederations to avoid internal black holes
b) or MPLS is enabled, an LSP exists with destination = BGP next-hop, in this case a BGP free core can exist and internal MPLS routers don't need to know how to route the packet just how to switch the MPLS frame that carries the packet inside itself.
in several providers both conditions are true if a BGP free core is not present.
with MPLS two levels of recursion can happen:
BGP choices the BGP next-hop
the BGP next-hop is used to check IGP routing table and MPLS forwarding table
traffic is sent over an LSP with destination = BGP next hop
the IP packet is encapsulated in an MPLS frame with label value = the value expected by next router in the path to destination
Hope to help
Giuseppe
06-04-2010 12:44 PM
Hello giuslar. Thx for the detailed response. Taking MPLS and route reflectors/confeds out of the equation, can I assume from your response that my initial assumption of the workings between IBGP and OSPF are correct? Thanks,
06-04-2010 01:51 PM
Hello,
yes, your understanding or recursion is correct
Hope to help
Giuseppe
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