Additional Tunnels for MPLS routers

[Venison Mogambi]

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?

[Nagendra Kumar Nainar]

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

[Venison Mogambi]

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)

[Nagendra Kumar Nainar]

yes, that is expected.