bail on small networks, serve complete range and exclude self

2 files changed, 12 insertions, 6 deletions

diff --git a/dhcpd.conf b/dhcpd.conf
index 6ec2a13..e0e295a 100644
--- a/dhcpd.conf
+++ b/dhcpd.conf
@@ -18,6 +18,12 @@ subnet __NETADDRESS__ netmask __NETMASK__ {
 	option time-servers __ADDRESS__;
 
 	range dynamic-bootp __MINHOST__ __MAXHOST__;
+
+	# make sure we do not serve our own address
+	host localhost {
+		hardware ethernet de:ad:00:be:ef:00;
+		fixed-address __ADDRESS__;
+	}
 }
 
 class "PXEClient" {
diff --git a/dyndhcpd.c b/dyndhcpd.c
index d6743f1..883349d 100644
--- a/dyndhcpd.c
+++ b/dyndhcpd.c
@@ -154,14 +154,14 @@ int main(int argc, char ** argv) {
 		s_broadcast.s_addr = v_host->s_addr |~ v_mask->s_addr;
 		s_netaddress.s_addr = v_host->s_addr & v_mask->s_addr;
 
-		if (ntohl(s_broadcast.s_addr) - ntohl(v_host->s_addr) < ntohl(v_host->s_addr) - ntohl(s_netaddress.s_addr)) {
-			s_minhost.s_addr = htonl(ntohl(s_netaddress.s_addr) + 1);
-			s_maxhost.s_addr = htonl(ntohl(v_host->s_addr) - 1);
-		} else {
-			s_minhost.s_addr = htonl(ntohl(v_host->s_addr) + 1);
-			s_maxhost.s_addr = htonl(ntohl(s_broadcast.s_addr) - 1);
+		if (ntohl(s_broadcast.s_addr) - ntohl(s_netaddress.s_addr) < 2) {
+			fprintf(stderr, "We do not have addresses to serve, need a netmask with 28 bit minimum.\n");
+			return EXIT_FAILURE;
 		}
 
+		s_minhost.s_addr = htonl(ntohl(s_netaddress.s_addr) + 1);
+		s_maxhost.s_addr = htonl(ntohl(s_broadcast.s_addr) - 1);
+
 		if (inet_ntop(AF_INET, &s_broadcast, c_broadcast, INET_ADDRSTRLEN) != NULL &&
 				inet_ntop(AF_INET, &s_netaddress, c_netaddress, INET_ADDRSTRLEN) != NULL &&
 				inet_ntop(AF_INET, &s_minhost, c_minhost, INET_ADDRSTRLEN) != NULL &&