H3C Technologies H3C S12500 Series Switches - Manual (Page 236)

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Solution
1. The common cause is that the physical interface of the tunnel source is not up. Use the display
interface tunnel or display ipv6 interface tunnel command to check whether the physical interface
of the tunnel source is up. If the physical interface is down, check the network connections.
2. Another possible cause is that the tunnel destination is unreachable. Use the display ipv6
routing-table or display ip routing-table command to check whether the tunnel destination is
reachable. If no routing entry is available for tunnel communication in the routing table, configure
a route to reach the tunnel destination.