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dhcp: Honour broadcast flag (RFC 2131, 4.1)

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It's widely considered a legacy option nowadays, and I've haven't seen
clients setting it since Windows 95, but it's convenient for a minimal
DHCP client not using raw IP sockets such as what I'm playing with for
muvm.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
Stefano Brivio 2024-11-25 00:52:57 +01:00
parent 9da2038485
commit c0fbc7ef2a
2 changed files with 13 additions and 2 deletions
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12
dhcp.c
View File

@ -112,6 +112,8 @@ struct msg {
uint32_t xid;
uint16_t secs;
uint16_t flags;
#define FLAG_BROADCAST htons_constant(0x8000)
uint32_t ciaddr;
struct in_addr yiaddr;
uint32_t siaddr;
@ -285,10 +287,10 @@ int dhcp(const struct ctx *c, const struct pool *p)
{
size_t mlen, dlen, offset = 0, opt_len, opt_off = 0;
char macstr[ETH_ADDRSTRLEN];
struct in_addr mask, dst;
const struct ethhdr *eh;
const struct iphdr *iph;
const struct udphdr *uh;
struct in_addr mask;
unsigned int i;
struct msg *m;
@ -400,7 +402,13 @@ int dhcp(const struct ctx *c, const struct pool *p)
opt_set_dns_search(c, sizeof(m->o));
dlen = offsetof(struct msg, o) + fill(m);
tap_udp4_send(c, c->ip4.our_tap_addr, 67, c->ip4.addr, 68, m, dlen);
if (m->flags & FLAG_BROADCAST)
dst = in4addr_broadcast;
else
dst = c->ip4.addr;
tap_udp4_send(c, c->ip4.our_tap_addr, 67, dst, 68, m, dlen);
return 1;
}

3
ip.h
View File

@ -101,4 +101,7 @@ static const struct in6_addr in6addr_ll_all_nodes = {
},
};
/* IPv4 Limited Broadcast (RFC 919, Section 7), 255.255.255.255 */
static const struct in_addr in4addr_broadcast = { 0xffffffff };
#endif /* IP_H */