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Add --dhcp-split-relay option.

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This makes a DHCPv4 relay which is functional when
client and server networks aren't mutually route-able.
This commit is contained in:
Simon Kelley
2025-07-25 18:47:33 +01:00
parent ea5b0e64e2
commit fc9f6985ab
8 changed files with 247 additions and 127 deletions
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122
src/dhcp.c
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@@ -32,8 +32,6 @@ static int complete_context(struct in_addr local, int if_index, char *label,
struct in_addr netmask, struct in_addr broadcast, void *vparam);
static int check_listen_addrs(struct in_addr local, int if_index, char *label,
struct in_addr netmask, struct in_addr broadcast, void *vparam);
static void relay_upstream4(int iface_index, struct dhcp_packet *mess, size_t sz);
static struct dhcp_relay *relay_reply4(struct dhcp_packet *mess, char *arrival_interface);
static int make_fd(int port)
{
@@ -344,7 +342,7 @@ void dhcp_packet(time_t now, int pxe_fd)
if (!iface_enumerate(AF_INET, &parm, (callback_t){.af_inet=complete_context}))
return;
relay_upstream4(iface_index, mess, (size_t)sz);
relay_upstream4(iface_index, mess, (size_t)sz, unicast_dest);
/* May have configured relay, but not DHCP server */
if (!daemon->dhcp)
@@ -1091,122 +1089,4 @@ char *host_from_dns(struct in_addr addr)
return NULL;
}
static void relay_upstream4(int iface_index, struct dhcp_packet *mess, size_t sz)
{
struct in_addr giaddr = mess->giaddr;
u8 hops = mess->hops;
struct dhcp_relay *relay;
if (mess->op != BOOTREQUEST)
return;
for (relay = daemon->relay4; relay; relay = relay->next)
if (relay->iface_index != 0 && relay->iface_index == iface_index)
break;
/* No relay config. */
if (!relay)
return;
for (; relay; relay = relay->next)
if (relay->iface_index != 0 && relay->iface_index == iface_index)
{
union mysockaddr to;
union all_addr from;
mess->hops = hops;
mess->giaddr = giaddr;
if ((mess->hops++) > 20)
continue;
/* source address == relay address */
from.addr4 = relay->local.addr4;
/* already gatewayed ? */
if (giaddr.s_addr)
{
/* if so check if by us, to stomp on loops. */
if (giaddr.s_addr == relay->local.addr4.s_addr)
continue;
}
else
{
/* plug in our address */
mess->giaddr.s_addr = relay->local.addr4.s_addr;
}
to.sa.sa_family = AF_INET;
to.in.sin_addr = relay->server.addr4;
to.in.sin_port = htons(relay->port);
#ifdef HAVE_SOCKADDR_SA_LEN
to.in.sin_len = sizeof(struct sockaddr_in);
#endif
/* Broadcasting to server. */
if (relay->server.addr4.s_addr == 0)
{
struct ifreq ifr;
if (relay->interface)
safe_strncpy(ifr.ifr_name, relay->interface, IF_NAMESIZE);
if (!relay->interface || strchr(relay->interface, '*') ||
ioctl(daemon->dhcpfd, SIOCGIFBRDADDR, &ifr) == -1)
{
my_syslog(MS_DHCP | LOG_ERR, _("Cannot broadcast DHCP relay via interface %s"), relay->interface);
continue;
}
to.in.sin_addr = ((struct sockaddr_in *) &ifr.ifr_addr)->sin_addr;
}
#ifdef HAVE_DUMPFILE
{
union mysockaddr fromsock;
fromsock.in.sin_port = htons(daemon->dhcp_server_port);
fromsock.in.sin_addr = from.addr4;
fromsock.sa.sa_family = AF_INET;
dump_packet_udp(DUMP_DHCP, (void *)mess, sz, &fromsock, &to, -1);
}
#endif
send_from(daemon->dhcpfd, 0, (char *)mess, sz, &to, &from, 0);
if (option_bool(OPT_LOG_OPTS))
{
inet_ntop(AF_INET, &relay->local, daemon->addrbuff, ADDRSTRLEN);
if (relay->server.addr4.s_addr == 0)
snprintf(daemon->dhcp_buff2, DHCP_BUFF_SZ, _("broadcast via %s"), relay->interface);
else
inet_ntop(AF_INET, &relay->server.addr4, daemon->dhcp_buff2, DHCP_BUFF_SZ);
my_syslog(MS_DHCP | LOG_INFO, _("DHCP relay at %s -> %s"), daemon->addrbuff, daemon->dhcp_buff2);
}
}
/* restore in case of a local reply. */
mess->giaddr = giaddr;
}
static struct dhcp_relay *relay_reply4(struct dhcp_packet *mess, char *arrival_interface)
{
struct dhcp_relay *relay;
if (mess->giaddr.s_addr == 0 || mess->op != BOOTREPLY)
return NULL;
for (relay = daemon->relay4; relay; relay = relay->next)
{
if (mess->giaddr.s_addr == relay->local.addr4.s_addr)
{
if (!relay->interface || wildcard_match(relay->interface, arrival_interface))
return relay->iface_index != 0 ? relay : NULL;
}
}
return NULL;
}
#endif