Instead of introduction: micro-FAQ.

• Q: In linux-2.0.36 I used:

   
      ifconfig tunl1 10.0.0.1 pointopoint 193.233.7.65
  

  to create tunnel. It does not work in 2.2.0!

  A: You are right, it does not work. The command written above is split to two commands.

      ip tunnel add MY-TUNNEL mode ipip remote 193.233.7.65
  

  will create tunnel device with name MY-TUNNEL. Now you may configure it with:

   
      ifconfig MY-TUNNEL 10.0.0.1
  

  Certainly, if you prefer name tunl1 to MY-TUNNEL, you still may use it.

• Q: In linux-2.0.36 I used:

   
      ifconfig tunl0 10.0.0.1
      route add -net 10.0.0.0 gw 193.233.7.65 dev tunl0
  

  to tunnel net 10.0.0.0 via router 193.233.7.65. It does not work in 2.2.0! Moreover, route prints a funny error sort of ``network unreachable'' and after this I found a strange direct route to 10.0.0.0 via tunl0 in routing table.

  A: Yes, in 2.2 the rule that normal gateway must reside on directly connected network has not any exceptions. You may tell kernel, that this particular route is abnormal:

   
    ifconfig tunl0 10.0.0.1 netmask 255.255.255.255
    ip route add 10.0.0.0/8 via 193.233.7.65 dev tunl0 onlink
  

  Note keyword onlink, it is the magic key that orders kernel not to check for consistency of gateway address. Probably, after this explanation you have already guessed another method to cheat kernel:

   
    ifconfig tunl0 10.0.0.1 netmask 255.255.255.255
    route add -host 193.233.7.65 dev tunl0
    route add -net 10.0.0.0 netmask 255.0.0.0 gw 193.233.7.65
    route del -host 193.233.7.65 dev tunl0
  

  Well, if you like such tricks, nobody may prohibit you to use them. Only do not forget that between route add and route del host 193.233.7.65 is unreachable.

• Q: In 2.0.36 I used to load tunnel device module and ipip module. I cannot find any tunnel in 2.2!

  A: Linux-2.2 has single module ipip for both directions of tunneling and for all IPIP tunnel devices.

• Q: traceroute does not work over tunnel! Well, stop... It works, only skips some number of hops.

  A: Yes. By default tunnel driver copies ttl value from inner packet to outer one. It means that path traversed by tunneled packets to another endpoint is not hidden. If you dislike this, or if you are going to use some routing protocol expecting that packets with ttl 1 will reach peering host (f.e. RIP, OSPF or EBGP) and you are not afraid of tunnel loops, you may append option ttl 64, when creating tunnel with ip tunnel add.

• Q: ... Well, list of things, which 2.0 was able to do finishes.