ip tunnel add has several additional options.
ttl N-- set fixed TTL
Non tunneled packets.
Nis number in the range 1-255. 0 is special value, meaning that packets inherit TTL value. Default value is:
tos T-- set fixed tos
Ton tunneled packets. Default value is:
dev DEV-- bind tunnel to device
DEV, so that tunneled packets will be routed only via this device and will not be able to escape to another device, when route to endpoint changes.
nopmtudisc-- disable Path MTU Discovery on this tunnel. It is enabled by default. Note that fixed ttl is incompatible with this option: tunnels with fixed ttl always make pmtu discovery.
sit tunnels have no more options.
tunnels are more complicated:
key K-- use keyed GRE with key
Kis either number or IP address-like dotted quad.
csum-- checksum tunneled packets.
seq-- serialize packets. 1cm NB. I think this option does not work. At least, I did not test it, did not debug it and even do not understand, how it is supposed to work and for what purpose Cisco planned to use it.
Actually, these GRE options can be set separately for input and
output directions by prefixing corresponding keywords with letter
icsum orders to accept only
packets with correct checksum and
ocsum means, that
our host will calculate and send checksum.
ip tunnel add is not the only operation,
which can be made with tunnels. Certainly, you may get short help page
ip tunnel help
Besides that, you may view list of installed tunnels with the help of command:
ip tunnel lsAlso you may look at statistics:
ip -s tunnel ls Ciscowhere
Ciscois name of tunnel device. Command
ip tunnel del Ciscodestroys tunnel
Cisco. And, finally,
ip tunnel change Cisco mode sit local ME remote HE ttl 32changes its parameters.