RD&RT two vrf inter-communication

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Apr 22nd, 2009
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if i have vrf-A and vrf-B.

VRF-A has a Prefix subnet-A and using OSPF.


i let subnet-a to export to VRF-B.

i wnat to know it use what routing protocol or method to export prxpix ?

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shivlu jain Wed, 04/22/2009 - 08:40
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for this only route target will work. It is the extended community which is used to install the route from one vrf to another.


shivlu jain

Hsin An Chen Mon, 04/27/2009 - 03:11
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i see , but i wnat to know it use what routing protocol or method to export prxpix ?

becausee i seen it used i-bgp bewteen two VRFs.

Giuseppe Larosa Mon, 04/27/2009 - 10:36
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Hello Hsin,

the signalling infrastructure in the Service provider uses multiprotocol iBGP:

L3 VPN prefixes are sent by PE routers as VPNv4 prefixes that is made of:

64 bit or RD + 32 bit IP address

this is to manage address overlapping

other PEs import vpnv4 routes in their locally defined VRFs, only if at least one route target extended community associated with the vpnv4 prefix matches a rt value that can be imported in the local VRF(s).

In case of import the RD is removed the ipv4 prefix is inserted in the VRF routing table.

The prefix appears as BGP [200 x] via the remote PE loopback (general routing table next-hop not provided to the CE)

PE-CE routing protocols choices include:

static routes

eBGP sessions (in VRF on the PE side)

RIP ( in address-family vrf vrf-name on PE side)

EIGRP ( in address-family vrf vrf-name on PE side)

OSPF (one process is associated to the VRF)

when using a protocol different then eBGP redistribution is mutual on PE between BGP in af vrf vrf-name and the IGP in the appropriate context (see above).

iBGP betweeen two VRFs:

this is a recent feature that allows to have a back to back iBGP session between a PE and a multi-VRF CE.

Before this was not allowed.

Hope to help



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