Hi Yuxiao,
On 11/09/2026 00:32, Yuxiao Zhang wrote:
> dhcpv6 is a special UDP traffic and should always use link local
> addresses. Only pick net_ip6 if it is not empty and if it is not dhcp6.
>
> Signed-off-by: Yuxiao Zhang <[email protected]>
> ---
>
> net/net6.c | 13 ++++++++-----
> 1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/net/net6.c b/net/net6.c
> index 4cff98df15c..18072bd9f49 100644
> --- a/net/net6.c
> +++ b/net/net6.c
> @@ -330,6 +330,10 @@ int net_send_udp_packet6(uchar *ether, struct in6_addr
> *dest, int dport,
> uchar *pkt;
> struct udp_hdr *udp;
> u16 csum_p;
> + struct in6_addr *src =
> + (dport == 547 || ip6_is_unspecified_addr(&net_ip6)) ?
> + &net_link_local_ip6 :
> + &net_ip6;
Rather than special-casing DHCPv6 based on dport == 547, I think this
should be based on the destination address scope.
For a link-local multicast destination, RFC 6724 source-address selection
prefers a link-local source address, so something like:
struct in6_addr *src =
(ip6_is_unspecified_addr(&net_ip6) ||
ip6_is_link_local_multicast(dest)) ?
&net_link_local_ip6 : &net_ip6;
with:
static bool ip6_is_link_local_multicast(const struct in6_addr *addr)
{
return addr->s6_addr[0] == 0xff &&
(addr->s6_addr[1] & 0xf) == 0x2;
}
This should fix DHCPv6 while keeping the source-address selection in the
IPv6 layer rather than making generic UDP code aware of DHCP port numbers.
What do you think?
> udp = (struct udp_hdr *)((uchar *)net_tx_packet + net_eth_hdr_size() +
> IP6_HDR_SIZE);
> @@ -341,7 +345,7 @@ int net_send_udp_packet6(uchar *ether, struct in6_addr
> *dest, int dport,
> /* checksum */
> udp->udp_xsum = 0;
> csum_p = csum_partial((u8 *)udp, len + UDP_HDR_SIZE, 0);
> - udp->udp_xsum = csum_ipv6_magic(&net_ip6, dest, len + UDP_HDR_SIZE,
> + udp->udp_xsum = csum_ipv6_magic(src, dest, len + UDP_HDR_SIZE,
> IPPROTO_UDP, csum_p);
>
> /* if MAC address was not discovered yet, save the packet and do
> @@ -353,8 +357,8 @@ int net_send_udp_packet6(uchar *ether, struct in6_addr
> *dest, int dport,
>
> pkt = net_nd_tx_packet;
> pkt += net_set_ether(pkt, net_nd_packet_mac, PROT_IP6);
> - pkt += ip6_add_hdr(pkt, &net_ip6, dest, IPPROTO_UDP, 64,
> - len + UDP_HDR_SIZE);
> + pkt += ip6_add_hdr(pkt, src, dest, IPPROTO_UDP, 64,
> + len + UDP_HDR_SIZE);
> memcpy(pkt, (uchar *)udp, len + UDP_HDR_SIZE);
>
> /* size of the waiting packet */
> @@ -370,8 +374,7 @@ int net_send_udp_packet6(uchar *ether, struct in6_addr
> *dest, int dport,
>
> pkt = (uchar *)net_tx_packet;
> pkt += net_set_ether(pkt, ether, PROT_IP6);
> - pkt += ip6_add_hdr(pkt, &net_ip6, dest, IPPROTO_UDP, 64,
> - len + UDP_HDR_SIZE);
> + pkt += ip6_add_hdr(pkt, src, dest, IPPROTO_UDP, 64, len + UDP_HDR_SIZE);
> (void)eth_send(net_tx_packet, pkt - net_tx_packet + UDP_HDR_SIZE + len);
>
> return 0; /* transmitted */
> ---
> base-commit: b4ac71db13a33c4e6532c60a781ddf34b7f4375a
> branch: main
>
Thanks,
--
Jerome
