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Refactor DHCP implementation to comply with RFC 2131 #57

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Merged
grossmj merged 1 commit into from
Nov 23, 2025
Merged

Refactor DHCP implementation to comply with RFC 2131 #57

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2 changes: 1 addition & 1 deletion src/command.c
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Original file line number Diff line number Diff line change
Expand Up @@ -693,7 +693,7 @@ static int run_dhcp_new(int renew, int dump)
i = 0;
ok = 0;
while (i < 3 && !ok) {
m = dhcp4_request(pc);
m = dhcp4_request(pc, renew);
if (m == NULL) {
printf("out of memory\n");
return 0;
Expand Down
45 changes: 37 additions & 8 deletions src/dhcp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -90,6 +90,7 @@ struct packet * dhcp4_discover(pcs *pc, int renew)
memcpy(&dh->options[i], pc->ip4.mac, 6);
i += 6;

/* For renewing and rebinding, include the requested IP address */
if (renew && pc->ip4.dhcp.ip) {
dh->options[i++] = DHO_DHCP_REQUESTED_ADDRESS;
dh->options[i++] = 4;
Expand Down Expand Up @@ -124,13 +125,17 @@ struct packet * dhcp4_discover(pcs *pc, int renew)
ip->cksum = 0;
ip->cksum = cksum((u_short *)ip, sizeof(iphdr));

encap_ehead(m->data, pc->ip4.mac, bcast, ETHERTYPE_IP);
/* For renewing, use unicast to the known server MAC; for initial discovery and rebinding, use broadcast */
if (renew)
encap_ehead(m->data, pc->ip4.mac, pc->ip4.dhcp.smac, ETHERTYPE_IP);
else
encap_ehead(m->data, pc->ip4.mac, bcast, ETHERTYPE_IP);
m->len = sizeof(ethdr) + sizeof(udpiphdr) + sizeof(dhcp4_hdr);

return m;
}

struct packet * dhcp4_request(pcs *pc)
struct packet * dhcp4_request(pcs *pc, int stage)
{
ethdr *eh;
iphdr *ip;
Expand All @@ -139,6 +144,7 @@ struct packet * dhcp4_request(pcs *pc)
int i, k;
struct packet *m;
char b[9];
u_char bcast[6] = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff};

m = new_pkt(DHCP4_PSIZE);
if (m == NULL)
Expand All @@ -156,7 +162,15 @@ struct packet * dhcp4_request(pcs *pc)
dh->xid = pc->ip4.dhcp.xid;
dh->secs = 0;
dh->flags = 0;
dh->ciaddr = pc->ip4.dhcp.ip;
/* For different stages, set appropriate client IP address */
/* stage == 0: Initial DHCP request (0.0.0.0) */
/* stage == 1: Renewing request (client's IP) */
/* stage == 2: Rebinding request (client's IP) */
if (stage == 0) {
dh->ciaddr = 0; /* 0.0.0.0 for initial request */
} else {
dh->ciaddr = pc->ip4.dhcp.ip; /* Client's IP for renewing/rebinding */
}
dh->yiaddr = 0;
dh->siaddr = 0;
dh->giaddr = 0;
Expand Down Expand Up @@ -214,8 +228,18 @@ struct packet * dhcp4_request(pcs *pc)
ip->ttl = 16;
ip->proto = IPPROTO_UDP;
ip->cksum = 0;
ip->sip = 0;
ip->dip = 0xffffffff;

/* For different stages, use appropriate IP addresses */
if (stage == 1) {
ip->sip = pc->ip4.dhcp.ip; /* Client's IP */
ip->dip = pc->ip4.dhcp.svr; /* Server's IP */
} else if (stage == 2) {
ip->sip = pc->ip4.dhcp.ip; /* Client's IP for rebinding */
ip->dip = 0xffffffff; /* 255.255.255.255 for broadcast */
} else {
ip->sip = 0; /* 0.0.0.0 for initial request */
ip->dip = 0xffffffff; /* 255.255.255.255 for broadcast */
}

bcopy(((struct ipovly *)ip)->ih_x1, b, 9);
bzero(((struct ipovly *)ip)->ih_x1, 9);
Expand All @@ -226,7 +250,12 @@ struct packet * dhcp4_request(pcs *pc)
ip->cksum = 0;
ip->cksum = cksum((u_short *)ip, sizeof(iphdr));

encap_ehead(m->data, pc->ip4.mac, pc->ip4.dhcp.smac, ETHERTYPE_IP);
/* For different stages, use appropriate destination MAC addresses */
if (stage == 1) {
encap_ehead(m->data, pc->ip4.mac, pc->ip4.dhcp.smac, ETHERTYPE_IP);
} else {
encap_ehead(m->data, pc->ip4.mac, bcast, ETHERTYPE_IP);
}
m->len = sizeof(ethdr) + sizeof(udpiphdr) + sizeof(dhcp4_hdr);

return m;
Expand Down Expand Up @@ -666,7 +695,7 @@ int dhcp_renew(pcs *pc)
i = 0;
ok = 0;
while (i++ < 3 && !ok) {
m = dhcp4_request(pc);
m = dhcp4_request(pc, 1);
if (m == NULL) {
sleep(1);
continue;
Expand Down Expand Up @@ -725,7 +754,7 @@ int dhcp_rebind(pcs *pc)
i = 0;
ok = 0;
while (!ok) {
m = dhcp4_request(pc);
m = dhcp4_request(pc, 2);
if (m == NULL) {
sleep(1);
continue;
Expand Down
2 changes: 1 addition & 1 deletion src/dhcp.h
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Original file line number Diff line number Diff line change
Expand Up @@ -81,7 +81,7 @@ typedef struct dhcp4_packet {
#define DHCP4_PSIZE (512)

struct packet * dhcp4_discover(pcs *pc, int renew);
struct packet * dhcp4_request(pcs *pc);
struct packet * dhcp4_request(pcs *pc, int stage);
struct packet * dhcp4_renew(pcs *pc);
struct packet * dhcp4_release(pcs *pc);
int isDhcp4_Offer(pcs *pc, struct packet *m);
Expand Down
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