Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
New Member

tunnel source dynamic command


The command documenation is very limited:

Can someone explain what this command is really supposed to do?

If I set it on the Tunnel interface which has a known destination I get a value of UNKNOWN for the Tunnel source.

I would like the Tunnel source to be dynamic in that the IOS chooses the IP address from the UP interface used in the path (route) to the destination, i.e.: outbound interface.

Thanks for any insight.


Current configuration : 489 bytes
interface Tunnel0
ip address
no ip redirects
ip mtu 1400
ip pim sparse-dense-mode
ip nhrp authentication XYZ
ip nhrp group XYZ_QOS
ip nhrp map multicast
ip nhrp map
ip nhrp network-id 111
ip nhrp holdtime 180
ip nhrp nhs
ip tcp adjust-mss 1360
qos pre-classify
tunnel source dynamic
tunnel destination
tunnel key 100111
tunnel protection ipsec profile XYZ

TESTRTR#sh int t0
Tunnel0 is up, line protocol is down
  Hardware is Tunnel
  Internet address is
  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 UNKNOWN, destination
  Tunnel protocol/transport GRE/IP
    Key 0x1870F, sequencing disabled
    Checksumming of packets disabled
  Tunnel TTL 255, Fast tunneling enabled
  Tunnel transport MTU 1472 bytes
  Tunnel transmit bandwidth 8000 (kbps)
  Tunnel receive bandwidth 8000 (kbps)
  Tunnel protection via IPSec (profile "XYZ")
  Last input never, output 00:30:59, output hang never
  Last clearing of "show interface" counters 00:58:18
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo (QOS pre-classification)
  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 IP multicasts)
     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

New Member

tunnel source dynamic command

Did I ask in the wrong forum maybe?


The only place I've seen

The only place I've seen "tunnel source dynamic" referenced is for IKEv2.  Maybe there are other uses, but in the IKEv2 example you'd use:

crypto ikev2 client flexvpn CRYPTO-IKEV2-CLIENT
  source 1 GigabitEthernet8 track 1
  source 2 GigabitEthernet9 track 2
  client connect Tunnel1

interface Tunnel1
  tunnel source dynamic



Re: tunnel source dynamic command

For a tunnel you are supposed to supply the two terminating end points. Using dynamic will not require you to configure the source address. You can connect to Internet anyways [may be with a dynamic IP address], the tunnel will be created. Pretty much what you have already stated.


New Member

tunnel source dynamic command

Yes that's what I would expect to happen, but it does not in practice.  So the qusetion remains, how and when is this command supposed to be used.


tunnel source dynamic command

Can you add 'tunnel mode gre multi'


CreatePlease to create content