Linux IPv6 HOWTO (en)
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9.2. Displaying existing tunnels

9.2.1. Using "ip"

Usage: 

# /sbin/ip -6 tunnel show [<device>]

Example: 

# /sbin/ip -6 tunnel show 
sit0: ipv6/ip remote any local any ttl 64 nopmtudisc 
sit1: ipv6/ip remote 195.226.187.50 local any ttl 64

9.2.2. Using "route"

Usage: 

# /sbin/route -A inet6

Example (output is filtered to display only tunnels through virtual interface sit0): 

# /sbin/route -A inet6 | grep "\Wsit0\W*$" 
::/96      ::               U   256  2  0  sit0 
2002::/16  ::               UA  256  0  0  sit0 
2000::/3   ::193.113.58.75  UG    1  0  0  sit0 
fe80::/10  ::               UA  256  0  0  sit0 
ff00::/8   ::               UA  256  0  0  sit0
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