Tunnel 0 IOS 15.0(1)M3

[mestridge]

After upgrading to IOS 15.0, we noticed that interface tunnel 0 in the show int description output; however, this interface does not show in the running config.  This interface (apparently a "hardware interface" cannot be removed or shutdown as one can't get into the tunnel interface 0 to do "anything".

Questions - Is this normal?  What issues present themselves with respect to EIGRP & DMVPN routing since tunnel 0 shares the same IP address as our DMVPN Tunnel?

Enter configuration commands, one per line.  End with CNTL/Z.
SNAP-3-N-RTR-2811(config)#int tunn 0
%Tunnel0 used by PIM for Registering, configuration not allowed
SNAP-3-N-RTR-2811(config)#shut
% Incomplete command.

SNAP-3-N-RTR-2811(config)#

Tunnel0 is up, line protocol is up
  Hardware is Tunnel
  Interface is unnumbered. Using address of Tunnel55 (z.z.z.3)
  MTU 17912 bytes, BW 100 Kbit/sec, DLY 50000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation TUNNEL, loopback not set
  Keepalive not set
  Tunnel source z.z.z.3 (Tunnel55), destination x.x.x.255
   Tunnel Subblocks:
      src-track:
         Tunnel0 source tracking subblock associated with Tunnel55
          Set of tunnels with source Tunnel55, 1 member (includes iterators), on interface <OK>
  Tunnel protocol/transport PIM/IPv4
  Tunnel TOS/Traffic Class 0xC0,  Tunnel TTL 255
  Tunnel transport MTU 1392 bytes
  Tunnel is transmit only
  Tunnel transmit bandwidth 8000 (kbps)
  Tunnel receive bandwidth 8000 (kbps)
  Last input never, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/0 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     0 packets output, 0 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 unknown protocol drops
     0 output buffer failures, 0 output buffers swapped out
SNAP-3-N-RTR-2811#sho run int tunn 55
Building configuration...

Current configuration : 671 bytes
!
interface Tunnel55
description DMVPN mGRE/IPSEC Tunnel
bandwidth 500
ip address z.z.z.3 255.255.255.0
no ip redirects
no ip proxy-arp
ip mtu 1420
ip pim nbma-mode
ip pim sparse-mode
ip nhrp authentication 55
ip nhrp map multicast dynamic
ip nhrp map multicast x.x.x.x.31
ip nhrp map y.y.y.55 x.x.x.31
ip nhrp network-id 55
ip nhrp holdtime 600
ip nhrp nhs y.y.y.55
ip nhrp shortcut
ip tcp adjust-mss 1368
load-interval 30
delay 1800
qos pre-classify
tunnel source Loopback1
tunnel mode gre multipoint
tunnel key 55
tunnel route-via FastEthernet0/0 mandatory
tunnel protection ipsec profile SWAN-IPSEC-PROFILE shared
!
end

Any and all assistance is greatly appreciated.

Kindest regards,

ME

[Peter Paluch]

Hello,

The Tunnel0 interface is not a hardware interface - rather it is a virtual interface created internally by the IOS to facilitate the multicast routing (the so-called PIM Register process where the multicast packets must first be tunelled to the Rendezvous Point router before a multicast distribution tree branch is created between the first-hop router and the RP to allow the multicast to flow natively). Do not be alarmed by this - it is normal.

This behavior started to manifest itself in IOS 15.0 but there have already been other reports of this behavior here on CSC. It is alright - simply ignore it.

Best regards,

Peter

[hipandya]

Hi,

I have the same issue with with tunnel 1 interface.

C2911-VSEC/K9  with IOS c2900-universalk9-mz.SPA.153-3.M5.bin

ROUTER_1(config)#interface tunnel 1
%Tunnel1 used by PIM for Registering, configuration not allowed
ROUTER_1(config)#ip address 100.X.X.31 255.255.255.0
                                       ^
% Invalid input detected at '^' marker.

Can any one explain what could be the issue and resolution. Thanks

[Peter Paluch]

Hello,

As I explained in my previous post, Tunnel1 on your particular router is a tunnel that is created automatically by IOS to facilitate registering multicast sources at the rendezvous point router (the PIM Register tunnel). You can not configure it and you are not supposed to - this PIM Register tunnel is created totally automatically by IOS for its internal needs and is not intended to be managed by you.

If you need to create a tunnel interface yourself, simply choose a different number than 1 - perhaps 2 or 11, for example.

Best regards,
Peter

[MujiCisco]

Hello Peter,

In my case I have a Tu0 that was created by the IOS when issued the command ip pim rp-address 10.x.x.x, as you have mentioned "to facilitate registering multicast sources at the rendezvous point router". However, the tunnel remains up/down and I think that's causing the SDA switch being unable to discover it. Is there any known cause for this?

Thank you and Regards

[Umesh Shetty]

Hi ,

As Peter said this is automatically created you will also see a description against it which is added.

Router#show interface description

Tu0                            up             up       Pim Register Tunnel (Encap) for RP x.x.x.x

Regards

Umesh

[Kanan Huseynli]

Hi,

you can use "show derived-config interface tunnel X" command to see configuration, however you can't configure it if it is automatically created for any reason. In your case tunnel is used for multicast PIM registration process (as colleagues explained).