Re: WWAN, PPP, and IPv6 configuration questions

[Dan Williams <dcbw redhat com>]

On Thu, 2014-04-10 at 14:01 -0500, Dan Williams wrote:
> Hi Tore!
>
> I'm slowly working on getting all the IPv6 pieces together and had a
> question about PPP & IPv6 that you might know.  I'm using the
> Icera-based Nokia 21M that you sent me long ago, and (due to some
> ModemManager bugs) it's using plain PPP.
>
> 1) What should the prefix be for the IPV6CP assigned address?  pppd
> hardcodes it as '10' which seems entirely bogus to me:
>
>     memset(&ifr6, 0, sizeof(ifr6));
>     IN6_LLADDR_FROM_EUI64(ifr6.ifr6_addr, our_eui64);
>     ifr6.ifr6_ifindex = ifr.ifr_ifindex;
>     ifr6.ifr6_prefixlen = 10;
>
>     if (ioctl(sock6_fd, SIOCSIFADDR, &ifr6) < 0) {
>
> Should it be 64? Should it 128?

Looking at RFC 2472 (IPV6CP) the '10' probably comes from:

Link-local addresses of PPP interfaces have the following format:

   | 10 bits  |        54 bits         |          64 bits            |
   +----------+------------------------+-----------------------------+
   |1111111010|           0            |    Interface Identifier     |
   +----------+------------------------+-----------------------------+

   The most significant 10 bits of the address is the Link-Local prefix
   FE80::.  54 zero bits pad out the address between the Link-Local
   prefix and the Interface Identifier fields.

Dan

> 2) Should anything bother to set the peer address on the PPP interface?
> For example, I get:
>
> local  LL address fe80::0000:0024:5c9b:0001
> remote LL address fe80::9d89:1690:be7b:438d
>
> with IPv4 we would do "ip addr add <local>/32 peer <remote> dev ppp0",
> should that same pattern be followed with IPv6?
>
> 3) Running RA on the PPP interface gives me yet another gateway:
>
> NetworkManager[21653]: --------- NMIP6Config 0x18d6db0 (WWAN-RA)
> NetworkManager[21653]:      gw: fe80::24:5c9b:40
> NetworkManager[21653]:     mss: 0
> NetworkManager[21653]:  n-dflt: 0
>
> What should be done with that, if anything?  Should that replace the
> peer address on ppp0?  Or should we just use it to set the default
> route, but leave the peer address the same?
>
> Thanks!
> Dan
>
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