Question on VRF Lite

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Hi,

Thank you for excellent explanation on VRF lite.
I understood how two customers passing through same ISP router cannot communicate each other. But I want not how their traffic pass upstream and how incoming traffic is divided to them?

Like,

Cust1 __PE1 --PE2/Internet
Cust2 |

Thankks.

@vishal-ranpariya said in Question on VRF Lite:

Hi,

Thank you for excellent explanation on VRF lite.
I understood how two customers passing through same ISP router cannot communicate each other. But I want not how their traffic pass upstream and how incoming traffic is divided to them?

Like,

Cust1 __PE1 --PE2/Internet
Cust2 |

Thankks.

I think I'm following but let me know if I'm not understanding your diagram correctly.

• Cust1 LAN will be routed by it's edge router (or switch) by the routing table if there is a route to it's destination.
• If the traffic is outbound, then it will be forwarded to the PE1 (VRF-lite Router) to do a VRF lookup and attaches a label for MPLS. This label will include the correct identifying info from Cust1 (usually VLAN info).
• Traffic crosses the MPLS network (WAN) to another VRF-lite Router, PE2. This router will read the label for the correct vlan information and look for the correct VLAN routing table to use.
• Router will then use a normal route lookup and to forward to the correct next hop to Cust2 LAN.

I hope this helps

@ronnie-wong

You got it right. Thanks for the reply.

Just to clear, it means if we want to move traffic upstream (or any other router) we need MPLS setup? Only VRF lite is not sufficient?

Also is there any way possible to have interface in two VRFs? What if there is one subnet (router running VRF or reachable through some interface on that router) which I want to allow for both the customers.

@vishal-ranpariya,

My apologies for not paying attention to the VRF Lite part.

You can do the same thing without MPLS using VRF lite it's similar to setting up for a Router on a Stick configuration using subinterfaces.

• create VRFs on your CE router
• create subinterfaces (similiar to a router on a stick configuration)
• assign VRF to each subinterface
• assign your each routing instance to each VRF instance

The PE will be able to route traffic back to each VRF enabled subinterface.

@ronnie-wong
Also is there any way possible to have interface in two VRFs? What if there is one subnet (on the router running VRF or reachable from that router) which I want to allow for both the customers?

@vishal-ranpariya,

You might try to configure static routing between your VRF to the IP address in another VRF.

The more traditional way after establishing your connectivity with vrf-lite between the same VRFs on different routers (e.g. RED to RED) is to run Multiprotocol BGP locally and enable VRF route import and export

Here's a great example with a great explanation: http://packetlife.net/blog/2010/mar/29/inter-vrf-routing-vrf-lite/

@ronnie-wong

Got it, Thank Ronnie.