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Re: slirp: Can I get IPv6-only DHCP working?

From: Peter Delevoryas
Subject: Re: slirp: Can I get IPv6-only DHCP working?
Date: Thu, 25 Aug 2022 16:15:26 -0700

On Fri, Aug 26, 2022 at 12:56:10AM +0200, Samuel Thibault wrote:
> Hello,
> Peter Delevoryas, le jeu. 25 août 2022 15:38:53 -0700, a ecrit:
> > It seems like there's support for an IPv6 dns proxy, and there's literally a
> > file called "dhcpv6.c" in slirp, but it has a comment saying it only 
> > supports
> > whatever is necessary for TFTP network boot I guess.
> For which DNS support is welcome :)
> > Maybe there's no support then?
> It seems there is:
>     if (ri.want_dns) {
>         *resp++ = OPTION_DNS_SERVERS >> 8; /* option-code high byte */
>         *resp++ = OPTION_DNS_SERVERS; /* option-code low byte */
>         *resp++ = 0; /* option-len high byte */
>         *resp++ = 16; /* option-len low byte */
>         memcpy(resp, &slirp->vnameserver_addr6, 16);
>         resp += 16;
>     }

Well, that's great, but actually I just care about whether slirp supports DHCPv6
address requests. Sorry if I didn't explain that properly.

My goal is to run:

    qemu-system-arm -machine fby35-bmc -nographic -mtdblock image-bmc \
        -net nic,model=ftgmac100,netdev=nic \
        -netdev user,id=nic,hostfwd=::2222-:22

And then see that the BMC received an IPv6 address assignment.

But, slirp currently just supports IP address assignment through BOOTP?  I
didn't realize that until looking a little closer at the code. But, since the
DHCPv6 hook "dhcpv6_input" is already there, maybe I can just get something
going through there? I suppose I might need some IPv6 NDP packets to work too,
to ssh through a hostfwd port.

    root@bmc-oob:~# ifconfig eth0
    eth0      Link encap:Ethernet  HWaddr FA:CE:B0:02:20:22
              inet addr:  Bcast:  Mask:
              inet6 addr: fec0::f8ce:b0ff:fe02:2022/64 Scope:Site
              inet6 addr: fe80::f8ce:b0ff:fe02:2022/64 Scope:Link
              UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
              RX packets:107 errors:0 dropped:0 overruns:0 frame:0
              TX packets:136 errors:0 dropped:0 overruns:0 carrier:0
              collisions:0 txqueuelen:1000
              RX bytes:13316 (13.0 KiB)  TX bytes:10022 (9.7 KiB)

Anyways, I'll do some more investigation on my own, thanks!

> Samuel

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