Question about Vrf-Lite

yuriz43

With VRF lite, are Route distinguishers necessary? I see them in a lot of peoples labs, and just don't see the point to it. I thought they are only required for MP-BGP / MPLS VPNs, since VPN-IPv4 addresses are a type of BGP address.

dtlokee

Are they really needed, probably not because the don't need to carry tags between routers only internally but some unique ID is required. I don't think I have seen a configuration example that does not have the RD set. I use them whenever I configure VRF Lite. It's possible that it will work but it may also cause unpredictable results.

yuriz43

Well, I had to lab this up! As expected, RD is not required for VRF-Lite.


Picture of lab
GNS3 Project File
Router configs

R0#show ip vrf
Name Default RD Interfaces
test1 <not set> Lo1
Fa0/0.1
test2 <not set> Lo2
Fa0/0.2
test3 <not set> Lo3
Fa0/0.3

R0#show ip int brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 unassigned YES unset up up
FastEthernet0/0.1 172.16.1.1 YES manual up up
FastEthernet0/0.2 172.16.1.1 YES manual up up
FastEthernet0/0.3 172.16.1.1 YES manual up up
Loopback1 10.0.0.1 YES manual up up
Loopback2 10.0.0.2 YES manual up up
Loopback3 10.0.0.3 YES manual up up




R0 is advertising each loopback via multiple OSPF instances (vrf test1, test2, and test3). Lets see how the routing looks on R1 now:



R1#show ip route vrf test1

172.16.0.0/24 is subnetted, 1 subnets
C 172.16.1.0 is directly connected, FastEthernet0/0.1
10.0.0.0/32 is subnetted, 1 subnets
O 10.0.0.1 [110/2] via 172.16.1.1, 00:11:33, FastEthernet0/0.1

R1#show ip route vrf test2

172.16.0.0/24 is subnetted, 1 subnets
C 172.16.1.0 is directly connected, FastEthernet0/0.2
10.0.0.0/32 is subnetted, 1 subnets
O 10.0.0.2 [110/2] via 172.16.1.1, 00:05:37, FastEthernet0/0.2

R1#show ip route vrf test3

172.16.0.0/24 is subnetted, 1 subnets
C 172.16.1.0 is directly connected, FastEthernet0/0.3
10.0.0.0/32 is subnetted, 1 subnets
O 10.0.0.3 [110/2] via 172.16.1.1, 00:05:26, FastEthernet0/0.3




I wouldn't be able to sleep without getting to the bottom of this. Any ways, I need to get back to the ISCW, I am getting side tracked again!! ( happens a lot with me because there are just so mainly details with each bit of technology you study )