iproute2

Documentation http://www.policyrouting.org/iproute2.doc.html#ss9.4.5

Tunnel

ip tunnel [$(ip tun)] --> show all tunnel

Create GRE tunnel

ip neigh state

nud is the state of ``neighbour unreachability detection for this entry. The full list of the possible nud states with minimal descriptions are: none --- state of the neighbour is void. incomplete --- the neighbour is in process of resolution. reachable --- the neighbour is valid and apparently reachable. stale --- the neighbour is valid, but probably it is already unreachable, so that kernel will try to check it at the first transmission. delay --- a packet has been sent to the stale neighbour, kernel waits for confirmation. probe --- delay timer expired, but no confirmation was received. Kernel has started to probe neighbour with ARP/NDISC messages. failed --- resolution has failed. noarp --- the neighbour is valid, no attempts to check the entry will be made. permanent --- it is noarp entry, but only administrator may remove the entry from neighbour table.