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From: | Thomas Huth |
Subject: | Re: slirp: Can I get IPv6-only DHCP working? |
Date: | Fri, 26 Aug 2022 09:21:12 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 |
On 26/08/2022 01.15, Peter Delevoryas wrote:
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.
No, slirp support "IPv6 *stateless* address assignment" (if you haven't heard about that before, I suggest to google it). That means that IPv6 addresses are not administered by a DHCP server, but that each client can built its own IPv6 address. It basically works like this (don't quote me on that, it's been a while since I worked with this stuff): Once the network interface of the client gets activated, the OS creates a link-local IPv6 that can be only used for activating on the link (based on the MAC address). It then uses this address for sending a "router solicitation" message, and if there is a router on the link, it replies with a "router advertisment" that contains a routable prefix. The client then can take this prefix to form a unique IPv6 address and assign it to its interface. QEMU/slirp support this way of address assignment, see ndp_send_na() in ip6_icmp.c. So if your BMC code supports stateless IPv6 address (it certainly should), you should be fine already).
HTH, Thomas
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