When/How are tunnel interfaces used?

[hikerguy]

I'm having some difficulty understanding how a tunnel interface is used. I get the basic config, but what traffic is sent across the tunnel?

Thanks

Tom

[megathumpzilla]

I believe for this test "tunnel" is talking about ipv4-ipv6 stacked mode.

[netdogo]

An IPsec tunnel is use to encrypt 'interesting' traffic. Here's an example that shows a tunnel that encrypts ICMP(ping) traffic.

http://www.netdogo.com/cisco-vpn-tunnel-...ec-tunnel/

The interesting traffic is defined by an access list. You can specify your normal ACL stuff like host/destination IP's, ports, TCP or UDP traffic, etc.

But that's way off topic for the CCNA, it's just looking for an overview of network security as it applies to Cisco devices.