VRF Across T1 Serial Link

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Jun 9th, 2010
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RouterA is connected to RouterB across a 1.54mbps T1. The WAN link is addressed with and runing ospf in area 0. I have a requirement for two seperate vrf's to be maintained aross the WAN link. How can this be done if there's only one /30 between the routers? A sample configuration would be great. Thanks in advance.

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Reza Sharifi Wed, 06/09/2010 - 18:26
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You have to use VRF-lite for that but you can not do it with 1 /30 subnet.  If you need 2 VRFs then you need two /30s.  It could also be one global with a /30 and one VRF with /30.

Here is a cofing guide on how to configure it:




Giuseppe Larosa Thu, 06/10/2010 - 03:25
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Hello David,

if you can enable MPLS between the two routers, that means to use the same IGP routing protocol, if you enable LDP you can use the serial link as an MPLS backbone link between the two PE nodes.

mpls ip

mpls ldp router-id loop0 force

! loop0's ip address has to be advertised in IGP

int ser0/0

mpls ip

and you need also BGP multiprotocol with VPNv4 address family and one address-family for each VRF

router bgp ASN

neigh PE2 remote-as ASN

neigh PE2 update-source loop0

address-family vpnv4

neigh PE2 activate

neigh PE2 send-community both

address-family ipv4 vrf VRFname1

red connected

! other commands here if needed

Hope to help


j-marenda Thu, 06/10/2010 - 04:08
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you may also use frame-relay encapsulation and configure two vc's ,

or, if the T1 line is structured, you may create two channel groups.



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