08-24-2016 05:58 AM
We've been extending MPLS down to some of our CE routers and I've noticed that when we enable MPLS on a router, several additional Tunnel interfaces are created automatically. Some of them are IP'd with our management Loopback IP, and other ones don't have an IP at all. Here's what they look like:
CE_router#sh ip int b
Loopback0 10.10.10.1 YES NVRAM up up
Tunnel0 10.10.10.1 YES unset up up
Tunnel1 unassigned YES unset up down
Tunnel2 10.10.10.1 YES unset up up
Tunnel3 10.10.10. YES unset up up
The Tunnels don't actually have a configuration though, e.g.:
CE_router#sh run int tun 3
Building configuration...
Current configuration : 5 bytes
end
Can someone explain why these tunnels are automatically created? Does it have something to do with the LSPs or different VRFs? Why do some of them inherit our configured Loopback IP, whereas others don't take an IP?
08-24-2016 07:37 AM
Hi,
For some features, tunnel will be automatically created (like MDT tunnel, PIM etc). Can you get the below:
1. Running configuration from the router.
2. show interface tunnel 0
-Nagendra
08-24-2016 08:05 AM
I can't really send the running config, but I did notice that at least some of the Tunnels are PIM Register Tunnels. I think there's one for each VRF and one for the Global routing table.
Here's an abbreviated "show int Tunnel" output for the tunnels:
Tunnel0 is up, line protocol is up
Hardware is Tunnel
Description: Pim Register Tunnel (Encap) for RP 110.10.10.1 on VRF RED
Tunnel1 is up, line protocol is down
Hardware is Tunnel
Description: Pim Register Tunnel (Encap) for RP 10.10.10.1 on VRF BLUE
Tunnel2 is up, line protocol is up
Hardware is Tunnel
Interface is unnumbered. Using address of Loopback0 (10.10.10.1)
08-24-2016 08:14 AM
yes, that is expected.
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