Subject: Question Regarding draft-rosen-vpns-ospf-bgp-mpls-05.txt

From: Shiv <[email-masked]>
Date: Mon, 16 Dec 2002 13:37:37 +0000

Hi,

I have a doubt regarding  draft-rosen-vpns-ospf-bgp-mpls-05.txt. Please
Consider the following topology.

       /  CE1---------------PE1--------------PE2---------CE3-----Site 2
Site1     I                                                  I
      \       I                                                  I
         CE2----------------

Site 1 and Site2 both belong to the same set of VPNs. Site 1 has two CEs

namely CE1 and CE2. Both the CEs are connected to PE1.Site 1 and Site 2
both
are running OSPF and belong to different areas but same domain.OSPF is
enabled on link CE1-PE1 and PE2-CE3. Note: OSPF is not enabled in link
CE2-PE1.Interface CE1-PE1 and CE2-PE1 are both mapped to the same VRF
say VRF1. In VRF1 redistribution of ospf routes into bgp is enabled.
Suppose Site 1 network say 10/8 is advertised to both CE1 and CE2. CE1
propagates OSPF route 10/8 to PE1 with next-hop CE1.
In PE1 a static route is configured in VRF1 for 10/8 with next-hop as
CE2.So VRF A will have two routes to reach 10/8 namely

1)ROUTE_1 :Destination - 10/8, Next-hop = CE1, Source Protocol - ospf
2)ROUTE_2: Destination - 10/8, Next-hop = CE2, Source Protocol - static

In VRF1, ROUTE_2 is the best route.  I have the following questions:

1) Which route ROUTE_1 or ROUTE_2 should be given to PE2. ROUTE_1 ,
ROUTE_2 or both.To be more precise, when ROUTE_1 and ROUTE_2 are sent to

PE2, their NEXT_HOP will be set to PE1(BGP Next-Hop). The main
difference between ROUTE_1 and ROUTE_2 will be "OSPF Route Type Extended

Communities Attribute".

It would be interesting to observe the following points. If we assume
that PE1-PE2 link is not present(i.e. PE1 and PE2 will together
constitute a router say PE).Site 1 and Site 2 constitiute a single
domain inter-AS OSPF network.  :
1) Then ROUTE_1 will  be propgated as type-3 LSA.
2)If redistribution from static to ospf is enabled. ROUTE_2 will be sent

as type-5 LSA. OSPF protocol will then take it's own course of action
and type-3 will be preferred.
Now If remove this assumption, PE1-PE2 will have IBGP peering. If
ROUTE_2 is sent after ROUTE_1, then IBGP in PE2 will consider ROUTE_2 as

a replacement route to ROUTE_1 and vice-versa. This will affect the OSPF

protocol functionality in the sense either ROUTE_1 or ROUTE_2 will be
considered as valid routes, but not both.

Thanks and Regards,
Shiv