emo/ndhc
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Add a heuristic to detect when server ignores dhcp renews.

Browse Source 
If we get no response to three renews (unicast), switch to sending
rebinds (broadcast).  Servers are supposed to always reply with
a DHCPACK or DHCPNAK even if the server doesn't update its internal
lease duration database, so this behavior should be RFC compliant.
This commit is contained in:
Nicholas J. Kain 2020-10-19 07:03:03 -04:00
parent f4365897bc
commit 32bc422d0e
2 changed files with 8 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
src/ndhc.h
View File

@ -48,7 +48,7 @@ struct client_state_t {
int epollFd, signalFd, listenFd, arpFd, nlFd, rfkillFd; int epollFd, signalFd, listenFd, arpFd, nlFd, rfkillFd;
int server_arp_sent, router_arp_sent; int server_arp_sent, router_arp_sent;
uint32_t nlPortId; uint32_t nlPortId;
unsigned int num_dhcp_requests; unsigned int num_dhcp_requests, num_dhcp_renews;
uint32_t clientAddr, serverAddr, srcAddr, routerAddr; uint32_t clientAddr, serverAddr, srcAddr, routerAddr;
uint32_t lease, xid; uint32_t lease, xid;
uint8_t routerArp[6], serverArp[6]; uint8_t routerArp[6], serverArp[6];

8
src/state.c
View File

@ -43,6 +43,8 @@
#include "netlink.h" #include "netlink.h"
#include "coroutine.h" #include "coroutine.h"
#define IGNORED_RENEWS_BEFORE_REBIND 3
#define SEL_SUCCESS 0 #define SEL_SUCCESS 0
#define SEL_FAIL -1 #define SEL_FAIL -1
@ -78,6 +80,7 @@ static void reinit_shared_deconfig(struct client_state_t cs[static 1])
cs->xid = nk_random_u32(&cs->rnd_state); cs->xid = nk_random_u32(&cs->rnd_state);
cs->clientAddr = 0; cs->clientAddr = 0;
cs->num_dhcp_requests = 0; cs->num_dhcp_requests = 0;
cs->num_dhcp_renews = 0;
cs->server_arp_sent = 0; cs->server_arp_sent = 0;
cs->router_arp_sent = 0; cs->router_arp_sent = 0;
cs->server_arp_state = ARP_QUERY; cs->server_arp_state = ARP_QUERY;
@ -150,7 +153,7 @@ static int renewing_timeout(struct client_state_t cs[static 1],
long long nowts) long long nowts)
{ {
long long rbt = cs->leaseStartTime + cs->rebindTime * 1000; long long rbt = cs->leaseStartTime + cs->rebindTime * 1000;
if (nowts >= rbt) if (nowts >= rbt || cs->num_dhcp_renews >= IGNORED_RENEWS_BEFORE_REBIND)
return rebinding_timeout(cs, nowts); return rebinding_timeout(cs, nowts);
start_dhcp_listen(cs); start_dhcp_listen(cs);
if (send_renew(cs) < 0) { if (send_renew(cs) < 0) {
@ -159,6 +162,7 @@ static int renewing_timeout(struct client_state_t cs[static 1],
return BTO_HARDFAIL; return BTO_HARDFAIL;
} }
cs->sent_renew_or_rebind = true; cs->sent_renew_or_rebind = true;
++cs->num_dhcp_renews;
long long ts0 = nowts + (50 + nk_random_u32(&cs->rnd_state) % 20) * 1000; long long ts0 = nowts + (50 + nk_random_u32(&cs->rnd_state) % 20) * 1000;
cs->dhcp_wake_ts = ts0 < rbt ? ts0 : rbt; cs->dhcp_wake_ts = ts0 < rbt ? ts0 : rbt;
return BTO_WAIT; return BTO_WAIT;
@ -230,6 +234,7 @@ static int extend_packet(struct client_state_t cs[static 1],
if (!validate_serverid(cs, packet, "a DHCP ACK")) if (!validate_serverid(cs, packet, "a DHCP ACK"))
return ANP_IGNORE; return ANP_IGNORE;
cs->sent_renew_or_rebind = false; cs->sent_renew_or_rebind = false;
cs->num_dhcp_renews = 0;
get_leasetime(cs, packet); get_leasetime(cs, packet);
// Did we receive a lease with a different IP than we had before? // Did we receive a lease with a different IP than we had before?
@ -253,6 +258,7 @@ static int extend_packet(struct client_state_t cs[static 1],
if (!validate_serverid(cs, packet, "a DHCP NAK")) if (!validate_serverid(cs, packet, "a DHCP NAK"))
return ANP_IGNORE; return ANP_IGNORE;
cs->sent_renew_or_rebind = false; cs->sent_renew_or_rebind = false;
cs->num_dhcp_renews = 0;
log_line("%s: Our request was rejected. Searching for a new lease...", log_line("%s: Our request was rejected. Searching for a new lease...",
client_config.interface); client_config.interface);
reinit_selecting(cs, 3000); reinit_selecting(cs, 3000);