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specifics of tunnel-related ifconfig commands

Started by cmusser, August 18, 2014, 01:38:21 PM

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I'm experimenting with using IPv6 via the HE tunnel broker on OpenBSD.
The tunnel works, but I want to confirm my understanding of the
commands given to set it up. These are the commands:

ifconfig gif0 tunnel
ifconfig gif0 inet6 alias 2001:470:1f04:204::2 2001:470:1f04:204::1 prefixlen 128
route -n add -inet6 default 2001:470:1f04:204::1

The first and third commands make sense to me; they set up an IPv4
tunnel interface and a default route for IPv6. I had to stare at the
second command (and the ifconfig(8) man page) for a while, so I'm
wondering if my understanding of it is correct.

The two IPv6 addresses provided by the tunnel broker are defined as
follows: <prefix>::1 is the "server IPv6 address" and <prefix>::2 is the
"client IPv6 address". Given that, are the following statements correct?

- <prefix>::1 is the local address of the interface on the IPv6

- The "alias" parameter is superfluous in this case. I tried it without
  that and got the same result: an operating tunnel.

- Because gif0 is a point-to-point interface, the <prefix>::2 (the
  server IP) is interpreted as the "dest_address" parameter mentioned
  in the ifconfig(8) man page.

- In non-point-to-point scenarios (for instance, if the machine were
  connected to an IPv6 network through the wired Ethernet interface),
  the "gateway" would be reachable because of the existence of the
  following two routes: a default route, (functionally identical to
  the example above), and a "network route" that forwards all traffic
  bound for the network on which the gateway exists to go through the
  Ethernet interface.

Thanks for any clarifications/corrections.