fixed the default interface for Linux to be eth0.

bacnet-stack/demo/server/Makefile

@@ -9,7 +9,7 @@ BASEDIR = .
 #DEFINES = -DBACFILE=1 -DPRINT_ENABLED=1 -DBIG_ENDIAN=0 -DBACDL_ETHERNET=1
 #DEFINES = -DBACFILE=1 -DPRINT_ENABLED=1 -DBIG_ENDIAN=0 -DBACDL_ARCNET=1
 #DEFINES = -DBACFILE=1 -DPRINT_ENABLED=1 -DBIG_ENDIAN=0 -DBACDL_MSTP=1
-DEFINES = -DBACFILE=1 -DPRINT_ENABLED=1 -DBIG_ENDIAN=0 -DBACDL_BIP=1
+DEFINES = -DBACFILE=1 -DPRINT_ENABLED=1 -DBIG_ENDIAN=0 -DBACDL_BIP=1 -DBIP_DEBUG
 BACNET_PORT = ../../ports/linux
 BACNET_OBJECT = ../object
 BACNET_HANDLER = ../handler

bacnet-stack/ports/linux/bip-init.c

@@ -82,6 +82,7 @@ static void bip_set_interface(char *ifname)
     get_local_address_ioctl(ifname, &local_address, SIOCGIFADDR);
     bip_set_addr(local_address.s_addr);
 #ifdef BIP_DEBUG
+    fprintf(stderr, "Interface: %s\n", ifname);
     fprintf(stderr, "IP Address: %s\n", inet_ntoa(local_address));
 #endif
     /* setup local broadcast address */
@@ -102,6 +103,9 @@ bool bip_init(char *ifname)
 
     if (ifname)
         bip_set_interface(ifname);
+    else
+        bip_set_interface("eth0");
+        
     /* assumes that the driver has already been initialized */
     sock_fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
     bip_set_socket(sock_fd);