Is Tunnel mode a mandatory command when configuring IPv6 Tunnels?

[lowfell]

I've asked a similar question before, but i still need a definitive clarity on this as I've had varied opinions

In this config, they have used "tunnel mode ipv6" 

interface Tunnel34
 no ip address
 ipv6 address 2026::34:1/122
 ipv6 enable
 ipv6 ospf 6 area 34
 tunnel source Serial0/0/0.34
 tunnel destination 10.1.1.10
 tunnel mode ipv6

Can you leave tunnel mode off altogether so the config would look like this?

interface Tunnel34
 no ip address
 ipv6 address 2026::34:1/122
 ipv6 enable
 ipv6 ospf 6 area 34
 tunnel source Serial0/0/0.34
 tunnel destination 10.1.1.10

[Georg Pauwen]

Hello,

'tunnel mode ipv6' is mandatory, without that command, the tunnel defaults to IP/GRE. Compare the output below:

With 'tunnel mode ipv6' configured:

Router#show interfaces tunnel 34

Tunnel protocol/transport IPv6

without 'tunnel mode ipv6' configured:

Router#show interfaces tunnel 34

Tunnel protocol/transport GRE/IP

[lowfell]

Hello George. would the tunnel still function WITHOUT tunnel mode statement?

You say it defaults to GRE/IP, so what difference would this make?

[Georg Pauwen · Accepted solution]

Hello,

the tunnel will function without the tunnel mode command, but not as an IPv6 tunnel.

What are you trying to accomplish ?

[lowfell]

I'm just trying to understand Tunnel configs for when i sit TSHOOT. I understand now that the tunnel mode obviously depends on the type of tunnel you are setting up.

So it's fare to say that if you source and destination are ipv4 addresses then you don't need tunnel mode whatever ?

Thanks for your help!

[Georg Pauwen]

Hello,

you are right. GRE is the default, so with source and destination being ipv4 addresses and no tunnel mode configured, GRE is what the tunnel will default to.

Depending on which IOS version you are using, the tunnel mode options are quite numerous:

http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/interface/command/ir-cr-book/ir-t2.html#wp4269279348

[lowfell]

Thanks for you help George.b