Merge pull request #13 from CoelacanthusHex/fix-makefile

chore: refine Makefile with Makefile Conventions

Constants.h

@@ -6,4 +6,10 @@
 
 #define MTU_MIN 74
 #define MTU_MAX 1522
-#define MTU_DEFAULT 329
+#define MTU_DEFAULT 329
+
+#define TXQUEUELEN 10
+
+// ARP timings, in seconds
+#define ARP_BASE_REACHABLE_TIME 300
+#define ARP_RETRANS_TIME 5

KISS.c

@@ -19,67 +19,67 @@ extern int device_type;
 extern void cleanup(void);
 
 void kiss_frame_received(int frame_len) {
-	if ( (device_type == IF_TUN && frame_len >= TUN_MIN_FRAME_SIZE) || (device_type == IF_TAP && frame_len >= ETHERNET_MIN_FRAME_SIZE) )  {
-		int written = write(attached_if, frame_buffer, frame_len);
-		if (written == -1) {
-			if (verbose && !daemonize) printf("Could not write received KISS frame (%d bytes) to network interface, is the interface up?\r\n", frame_len);
-		} else if (written != frame_len) {
-			if (!daemonize) printf("Error: Could only write %d of %d bytes to interface", written, frame_len);
-			cleanup();
-			exit(1);
-		}
-		if (verbose && !daemonize) printf("Got %d bytes from TNC, wrote %d bytes to interface\r\n", frame_len, written);
-	}
+    if ( (device_type == IF_TUN && frame_len >= TUN_MIN_FRAME_SIZE) || (device_type == IF_TAP && frame_len >= ETHERNET_MIN_FRAME_SIZE) )  {
+        int written = write(attached_if, frame_buffer, frame_len);
+        if (written == -1) {
+            if (verbose && !daemonize) printf("Could not write received KISS frame (%d bytes) to network interface, is the interface up?\r\n", frame_len);
+        } else if (written != frame_len) {
+            if (!daemonize) printf("Error: Could only write %d of %d bytes to interface", written, frame_len);
+            cleanup();
+            exit(1);
+        }
+        if (verbose && !daemonize) printf("Got %d bytes from TNC, wrote %d bytes to interface\r\n", frame_len, written);
+    }
 }
 
 void kiss_serial_read(uint8_t sbyte) {
-	if (IN_FRAME && sbyte == FEND && kiss_command == CMD_DATA) {
-	    IN_FRAME = false;
-	    kiss_frame_received(frame_len);
-	} else if (sbyte == FEND) {
-	    IN_FRAME = true;
-	    kiss_command = CMD_UNKNOWN;
-	    frame_len = 0;
-	} else if (IN_FRAME && frame_len < MAX_PAYLOAD) {
-	    // Have a look at the command byte first
-	    if (frame_len == 0 && kiss_command == CMD_UNKNOWN) {
-	    	// Strip of port nibble
-	        kiss_command = sbyte & 0x0F;
-	    } else if (kiss_command == CMD_DATA) {
-	        if (sbyte == FESC) {
-	            ESCAPE = true;
-	        } else {
-	            if (ESCAPE) {
-	                if (sbyte == TFEND) sbyte = FEND;
-	                if (sbyte == TFESC) sbyte = FESC;
-	                ESCAPE = false;
-	            }
+    if (IN_FRAME && sbyte == FEND && kiss_command == CMD_DATA) {
+        IN_FRAME = false;
+        kiss_frame_received(frame_len);
+    } else if (sbyte == FEND) {
+        IN_FRAME = true;
+        kiss_command = CMD_UNKNOWN;
+        frame_len = 0;
+    } else if (IN_FRAME && frame_len < MAX_PAYLOAD) {
+        // Have a look at the command byte first
+        if (frame_len == 0 && kiss_command == CMD_UNKNOWN) {
+            // Strip of port nibble
+            kiss_command = sbyte & 0x0F;
+        } else if (kiss_command == CMD_DATA) {
+            if (sbyte == FESC) {
+                ESCAPE = true;
+            } else {
+                if (ESCAPE) {
+                    if (sbyte == TFEND) sbyte = FEND;
+                    if (sbyte == TFESC) sbyte = FESC;
+                    ESCAPE = false;
+                }
 
-	            if (frame_len < MAX_PAYLOAD) {
-	            	frame_buffer[frame_len++] = sbyte;
-	            }
-	        }
-	    }
-	}
+                if (frame_len < MAX_PAYLOAD) {
+                    frame_buffer[frame_len++] = sbyte;
+                }
+            }
+        }
+    }
 }
 
 int kiss_write_frame(int serial_port, uint8_t* buffer, int frame_len) {
-	int write_len = 0;
-	write_buffer[write_len++] = FEND;
-	write_buffer[write_len++] = CMD_DATA;
-	for (int i = 0; i < frame_len; i++) {
-		uint8_t byte = buffer[i];
-		if (byte == FEND) {
-			write_buffer[write_len++] = FESC;
-			write_buffer[write_len++] = TFEND;
-		} else if (byte == FESC) {
-			write_buffer[write_len++] = FESC;
-			write_buffer[write_len++] = TFESC;
-		} else {
-			write_buffer[write_len++] = byte;
-		}
-	}
-	write_buffer[write_len++] = FEND;
+    int write_len = 0;
+    write_buffer[write_len++] = FEND;
+    write_buffer[write_len++] = CMD_DATA;
+    for (int i = 0; i < frame_len; i++) {
+        uint8_t byte = buffer[i];
+        if (byte == FEND) {
+            write_buffer[write_len++] = FESC;
+            write_buffer[write_len++] = TFEND;
+        } else if (byte == FESC) {
+            write_buffer[write_len++] = FESC;
+            write_buffer[write_len++] = TFESC;
+        } else {
+            write_buffer[write_len++] = byte;
+        }
+    }
+    write_buffer[write_len++] = FEND;
 
-	return write(serial_port, write_buffer, write_len);
+    return write(serial_port, write_buffer, write_len);
 }

README.md

@@ -6,7 +6,7 @@ Attach KISS TNC devices as network interfaces in Linux. This program allows you
 
 Currently it is recommended to compile and install __tncattach__ from source with the below commands.
 
-If that is not possible for you, precompiled __amd64__ and __armhf__ (Raspberry Pi and similar) binaries have been provided in the releases section. You can [download the latest release here](https://github.com/markqvist/tncattach/releases/tag/0.1.3).
+If that is not possible for you, precompiled __amd64__ and __armhf__ (Raspberry Pi and similar) binaries have been provided in the releases section. You can [download the latest release here](https://github.com/markqvist/tncattach/releases).
 
 ```sh
 # If you don't already have a compiler installed
@@ -34,14 +34,17 @@ Usage: tncattach [OPTION...] port baudrate
 
 Attach TNC devices as system network interfaces
 
-  -d, --daemon               Run tncattach as a daemon
+  -m, --mtu=MTU              Specify interface MTU
   -e, --ethernet             Create a full ethernet device
   -i, --ipv4=IP_ADDRESS      Configure an IPv4 address on interface
-  -m, --mtu=MTU              Specify interface MTU
   -n, --noipv6               Filter IPv6 traffic from reaching TNC
       --noup                 Only create interface, don't bring it up
-  -s, --id=CALLSIGN          Station identification data
+  -T, --kisstcp              Use KISS over TCP instead of serial port
+  -H, --tcphost=TCP_HOST     Host to connect to when using KISS over TCP
+  -P, --tcpport=TCP_PORT     TCP port when using KISS over TCP
   -t, --interval=SECONDS     Maximum interval between station identifications
+  -s, --id=CALLSIGN          Station identification data
+  -d, --daemon               Run tncattach as a daemon
   -v, --verbose              Enable verbose output
   -?, --help                 Give this help list
       --usage                Give a short usage message
@@ -50,6 +53,8 @@ Attach TNC devices as system network interfaces
 
 The program supports attaching TNCs as point-to-point tunnel devices, or generic ethernet devices. The ethernet mode is suitable for point-to-multipoint setups, and can be enabled with the corresponding command line switch. If you only need point-to-point links, it is advisable to just use the standard point-to-point mode, since it doesn't incur the ethernet header overhead on each packet.
 
+If you want to connect to a virtual KISS TNC over a TCP connection, you can use the -T option, along with the -H and -P options to specify the host and port.
+
 Additionally, it is worth noting that __tncattach__ can filter out IPv6 packets from reaching the TNC. Most operating systems attempts to autoconfigure IPv6 when an interface is brought up, which results in a substantial amount of IPv6 traffic generated by router solicitations and similar, which is usually unwanted for packet radio links and similar.
 
 If you intend to use __tncattach__ on a system with mDNS services enabled (avahi-daemon, for example), you may want to consider modifying your mDNS setup to exclude TNC interfaces, or turning it off entirely, since it will generate a lot of traffic that might be unwanted.
@@ -75,6 +80,13 @@ Create an ethernet device with a USB-connected TNC, set the MTU, filter IPv6 tra
 sudo tncattach /dev/ttyUSB0 115200 --ethernet --mtu 576 --noipv6 --ipv4 10.92.0.10/24
 ```
 
+Create an ethernet device with a TCP-connected TNC, set the MTU, filter IPv6 traffic, and set an IPv4 address:
+
+```sh
+# Attach interface
+sudo tncattach -T -H localhost -P 8001 --ethernet --mtu 576 --noipv6 --ipv4 10.92.0.10/24
+```
+
 You can interact with the interface like any other using the __ip__ or __ifconfig__ utilities:
 
 ```sh
@@ -111,3 +123,21 @@ tnc0: flags=4305<UP,POINTOPOINT,RUNNING,NOARP,MULTICAST>  mtu 400
         TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
 
 ```
+
+## Worth Knowing on Raspbian
+
+On some versions of Raspbian (and probably other operating systems), the DHCP client daemon _dhcpcd_ interferes with TNC interfaces, by overriding their MTU and trying to auto-configure link-local addresses. You probably don't want this, and it can be disabled by editing the __/etc/dhcpcd.conf__ file, adding a statement telling _dhcpcd_ to ignore your TNC interface:
+
+```
+# Add the following statement somewhere at the beginning
+# of /etc/dhcpcd.conf to prevent dhcpcd from changing MTU
+
+denyinterfaces tnc0
+```
+
+## Support tncattach development
+You can help support the continued development of open, free and private communications systems by donating via one of the following channels:
+
+- Ethereum: 0x81F7B979fEa6134bA9FD5c701b3501A2e61E897a
+- Bitcoin: 3CPmacGm34qYvR6XWLVEJmi2aNe3PZqUuq
+- Ko-Fi: https://ko-fi.com/markqvist

Serial.c

@@ -3,172 +3,172 @@
 extern void cleanup();
 
 int open_port(char* port) {
-	int fd;
-	fd = open(port, O_RDWR | O_NOCTTY | O_SYNC | O_NDELAY);
+    int fd;
+    fd = open(port, O_RDWR | O_NOCTTY | O_SYNC | O_NDELAY);
 
-	if (fd == -1) {
-		perror("The serial port could not be opened");
-		cleanup();
-		exit(1);
-	} else {
-		fcntl(fd, F_SETFL, 0);
-	}
+    if (fd == -1) {
+        perror("The serial port could not be opened");
+        cleanup();
+        exit(1);
+    } else {
+        fcntl(fd, F_SETFL, 0);
+    }
 
-	return fd;
+    return fd;
 }
 
 int close_port(int fd) {
-	return close(fd);
+    return close(fd);
 }
 
 void set_speed(void *tty_s, int speed) {
-	cfsetospeed(tty_s, speed);
-	cfsetispeed(tty_s, speed);
+    cfsetospeed(tty_s, speed);
+    cfsetispeed(tty_s, speed);
 }
 
 bool setup_port(int fd, int speed) {
-	struct termios tty;
-	if (tcgetattr(fd, &tty) != 0) {
-		perror("Error setting port speed, could not read port parameters");
-		return false;
-	}
+    struct termios tty;
+    if (tcgetattr(fd, &tty) != 0) {
+        perror("Error setting port speed, could not read port parameters");
+        return false;
+    }
 
-	switch (speed) {
-		case 0:
-			set_speed(&tty, B0);
-			break;
-		case 50:
-			set_speed(&tty, B50);
-			break;
-		case 75:
-			set_speed(&tty, B75);
-			break;
-		case 110:
-			set_speed(&tty, B110);
-			break;
-		case 134:
-			set_speed(&tty, B134);
-			break;
-		case 150:
-			set_speed(&tty, B150);
-			break;
-		case 200:
-			set_speed(&tty, B200);
-			break;
-		case 300:
-			set_speed(&tty, B300);
-			break;
-		case 600:
-			set_speed(&tty, B600);
-			break;
-		case 1200:
-			set_speed(&tty, B1200);
-			break;
-		case 2400:
-			set_speed(&tty, B2400);
-			break;
-		case 4800:
-			set_speed(&tty, B4800);
-			break;
-		case 9600:
-			set_speed(&tty, B9600);
-			break;
-		case 19200:
-			set_speed(&tty, B19200);
-			break;
-		case 38400:
-			set_speed(&tty, B38400);
-			break;
-		case 57600:
-			set_speed(&tty, B57600);
-			break;
-		case 115200:
-			set_speed(&tty, B115200);
-			break;
-		case 230400:
-			set_speed(&tty, B230400);
-			break;
-		default:
-			printf("Error: Invalid port speed %d specified\r\n", speed);
-			cleanup();
-			exit(1);
-			return false;
-	}
+    switch (speed) {
+        case 0:
+            set_speed(&tty, B0);
+            break;
+        case 50:
+            set_speed(&tty, B50);
+            break;
+        case 75:
+            set_speed(&tty, B75);
+            break;
+        case 110:
+            set_speed(&tty, B110);
+            break;
+        case 134:
+            set_speed(&tty, B134);
+            break;
+        case 150:
+            set_speed(&tty, B150);
+            break;
+        case 200:
+            set_speed(&tty, B200);
+            break;
+        case 300:
+            set_speed(&tty, B300);
+            break;
+        case 600:
+            set_speed(&tty, B600);
+            break;
+        case 1200:
+            set_speed(&tty, B1200);
+            break;
+        case 2400:
+            set_speed(&tty, B2400);
+            break;
+        case 4800:
+            set_speed(&tty, B4800);
+            break;
+        case 9600:
+            set_speed(&tty, B9600);
+            break;
+        case 19200:
+            set_speed(&tty, B19200);
+            break;
+        case 38400:
+            set_speed(&tty, B38400);
+            break;
+        case 57600:
+            set_speed(&tty, B57600);
+            break;
+        case 115200:
+            set_speed(&tty, B115200);
+            break;
+        case 230400:
+            set_speed(&tty, B230400);
+            break;
+        default:
+            printf("Error: Invalid port speed %d specified\r\n", speed);
+            cleanup();
+            exit(1);
+            return false;
+    }
 
-	// Set 8-bit characters, no parity, one stop bit
-	tty.c_cflag |= CS8;
-	tty.c_cflag &= ~PARENB;
-	tty.c_cflag &= ~CSTOPB;
+    // Set 8-bit characters, no parity, one stop bit
+    tty.c_cflag |= CS8;
+    tty.c_cflag &= ~PARENB;
+    tty.c_cflag &= ~CSTOPB;
 
-	// Disable hardware flow control
-	tty.c_cflag &= ~CRTSCTS;
+    // Disable hardware flow control
+    tty.c_cflag &= ~CRTSCTS;
 
-	// Enable reading and ignore modem
-	// control lines
-	tty.c_cflag |= CREAD | CLOCAL;
+    // Enable reading and ignore modem
+    // control lines
+    tty.c_cflag |= CREAD | CLOCAL;
 
-	// Disable canonical mode, echo
-	// and signal characters.
-	tty.c_lflag &= ~ICANON;
-	tty.c_lflag &= ~ECHO;
-	tty.c_lflag &= ~ECHOE;
-	tty.c_lflag &= ~ECHONL;
-	tty.c_lflag &= ~ISIG;
+    // Disable canonical mode, echo
+    // and signal characters.
+    tty.c_lflag &= ~ICANON;
+    tty.c_lflag &= ~ECHO;
+    tty.c_lflag &= ~ECHOE;
+    tty.c_lflag &= ~ECHONL;
+    tty.c_lflag &= ~ISIG;
 
-	// Disable processing of input,
-	// just pass the raw data.
-	tty.c_iflag &= ~(IGNBRK|BRKINT|PARMRK|ISTRIP|INLCR|IGNCR|ICRNL);
+    // Disable processing of input,
+    // just pass the raw data.
+    tty.c_iflag &= ~(IGNBRK|BRKINT|PARMRK|ISTRIP|INLCR|IGNCR|ICRNL);
 
-	// Disable XON/XOFF software flow control.
-	tty.c_iflag &= ~(IXON | IXOFF | IXANY);
+    // Disable XON/XOFF software flow control.
+    tty.c_iflag &= ~(IXON | IXOFF | IXANY);
 
-	// Disable processing output bytes
-	// and new line conversions
-	tty.c_oflag &= ~OPOST;
-	tty.c_oflag &= ~ONLCR;
+    // Disable processing output bytes
+    // and new line conversions
+    tty.c_oflag &= ~OPOST;
+    tty.c_oflag &= ~ONLCR;
 
-	// Block forever until at least one byte is read.
-	tty.c_cc[VMIN]   = 1;
-	tty.c_cc[VTIME]  = 0;
+    // Block forever until at least one byte is read.
+    tty.c_cc[VMIN]   = 1;
+    tty.c_cc[VTIME]  = 0;
 
-	// TODO: Check these
-	// Prevent conversion of tabs to spaces (NOT PRESENT IN LINUX)
-	// tty.c_oflag &= ~OXTABS;
-	// Prevent removal of C-d chars (0x004) in output (NOT PRESENT IN LINUX)
-	// tty.c_oflag &= ~ONOEOT;
+    // TODO: Check these
+    // Prevent conversion of tabs to spaces (NOT PRESENT IN LINUX)
+    // tty.c_oflag &= ~OXTABS;
+    // Prevent removal of C-d chars (0x004) in output (NOT PRESENT IN LINUX)
+    // tty.c_oflag &= ~ONOEOT;
 
-	if (tcsetattr(fd, TCSANOW, &tty) != 0) {
-		perror("Could not configure serial port parameters");
-		return false;
-	} else {
-		return true;
-	}
+    if (tcsetattr(fd, TCSANOW, &tty) != 0) {
+        perror("Could not configure serial port parameters");
+        return false;
+    } else {
+        return true;
+    }
 }
 
 bool set_port_blocking(int fd, bool should_block) {
-	struct termios tty;
-	memset(&tty, 0, sizeof tty);
+    struct termios tty;
+    memset(&tty, 0, sizeof tty);
 
-	if (tcgetattr(fd, &tty) != 0) {
-		perror("Error configuring port blocking behaviour, could not read port parameters");
-		return false;
-	} else {
-		// TODO: Implement this correctly
-		if (should_block) {
-			// Block forever until at least one byte is read.
-			tty.c_cc[VMIN]   = 1;
-			tty.c_cc[VTIME]  = 0;
-		} else {
-			// Never block, always return immediately with
-			// whatever is available.
-			tty.c_cc[VMIN]   = 0;
-			tty.c_cc[VTIME]  = 0;
-		}
-		if (tcsetattr(fd, TCSANOW, &tty) != 0) {
-			perror("Could not set port parameters while configuring blocking behaviour");
-			return false;
-		} else {
-			return true;
-		}
-	}
+    if (tcgetattr(fd, &tty) != 0) {
+        perror("Error configuring port blocking behaviour, could not read port parameters");
+        return false;
+    } else {
+        // TODO: Implement this correctly
+        if (should_block) {
+            // Block forever until at least one byte is read.
+            tty.c_cc[VMIN]   = 1;
+            tty.c_cc[VTIME]  = 0;
+        } else {
+            // Never block, always return immediately with
+            // whatever is available.
+            tty.c_cc[VMIN]   = 0;
+            tty.c_cc[VTIME]  = 0;
+        }
+        if (tcsetattr(fd, TCSANOW, &tty) != 0) {
+            perror("Could not set port parameters while configuring blocking behaviour");
+            return false;
+        } else {
+            return true;
+        }
+    }
 }

TAP.c

@@ -15,125 +15,184 @@ extern char* netmask;
 extern void cleanup();
 
 int open_tap(void) {
-	struct ifreq ifr;
-	int fd = open("/dev/net/tun", O_RDWR);
+    struct ifreq ifr;
+    int fd = open("/dev/net/tun", O_RDWR);
 
-	if (fd < 0) {
-		perror("Could not open clone device");
-		exit(1);
-	} else {
-		memset(&ifr, 0, sizeof(ifr));
-		// TODO: Enable PI header again?
+    if (fd < 0) {
+        perror("Could not open clone device");
+        exit(1);
+    } else {
+        memset(&ifr, 0, sizeof(ifr));
+        // TODO: Enable PI header again?
 
-		if (device_type == IF_TAP) {
-			ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
-		} else if (device_type == IF_TUN) {
-			ifr.ifr_flags = IFF_TUN;
-		} else {
-			printf("Error: Unsupported interface type\r\n");
-			cleanup();
-			exit(1);
-		}
+        if (device_type == IF_TAP) {
+            ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
+        } else if (device_type == IF_TUN) {
+            ifr.ifr_flags = IFF_TUN;
+        } else {
+            printf("Error: Unsupported interface type\r\n");
+            cleanup();
+            exit(1);
+        }
 
-		strcpy(tap_name, "tnc%d");
-		strncpy(ifr.ifr_name, tap_name, IFNAMSIZ);
+        strcpy(tap_name, "tnc%d");
+        strncpy(ifr.ifr_name, tap_name, IFNAMSIZ);
 
-		if (ioctl(fd, TUNSETIFF, &ifr) < 0) {
-			perror("Could not configure network interface");
-			exit(1);
-		} else {
-			strcpy(if_name, ifr.ifr_name);
-			
-			int inet = socket(AF_INET, SOCK_DGRAM, 0);
-			if (inet == -1) {
-				perror("Could not open AF_INET socket\r\n");
-				cleanup();
-				exit(1);
-			} else {
-				if (ioctl(inet, SIOCGIFFLAGS, &ifr) < 0) {
-					perror("Could not get interface flags from kernel");
-					close(inet);
-					cleanup();
-					exit(1);
-				} else {
-					ifr.ifr_mtu = mtu;
-					if (ioctl(inet, SIOCSIFMTU, &ifr) < 0) {
-						perror("Could not configure interface MTU");
-						close(inet);
-						cleanup();
-						exit(1);
-					}
+        if (ioctl(fd, TUNSETIFF, &ifr) < 0) {
+            perror("Could not configure network interface");
+            exit(1);
+        } else {
+            strcpy(if_name, ifr.ifr_name);
+            
+            int inet = socket(AF_INET, SOCK_DGRAM, 0);
+            if (inet == -1) {
+                perror("Could not open AF_INET socket");
+                cleanup();
+                exit(1);
+            } else {
+                if (ioctl(inet, SIOCGIFMTU, &ifr) < 0) {
+                    perror("Could not get interface flags from kernel");
+                    close(inet);
+                    cleanup();
+                    exit(1);
+                } else {
+                    ifr.ifr_mtu = mtu;
+                    if (ioctl(inet, SIOCSIFMTU, &ifr) < 0) {
+                        perror("Could not configure interface MTU");
+                        close(inet);
+                        cleanup();
+                        exit(1);
+                    }
 
-					if (!noup) {
-						if (ioctl(inet, SIOCGIFFLAGS, &ifr) < 0) {
-							perror("Could not get interface flags from kernel");
-							close(inet);
-							cleanup();
-							exit(1);
-						} else {
-							ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
-							if (ioctl(inet, SIOCSIFFLAGS, &ifr) < 0) {
-								perror("Could not bring up interface");
-								close(inet);
-								cleanup();
-								exit(1);
-							} else {
-								if (set_ipv4) {
-									struct ifreq a_ifr;
-									struct sockaddr_in addr, snm;
+                    // Configure TX queue length
+                    if (ioctl(inet, SIOCGIFTXQLEN, &ifr) < 0) {
+                        perror("Could not get interface flags from kernel");
+                        close(inet);
+                        cleanup();
+                        exit(1);
+                    } else {
+                        ifr.ifr_qlen = TXQUEUELEN;
+                        if (ioctl(inet, SIOCSIFTXQLEN, &ifr) < 0) {
+                            perror("Could not set interface TX queue length");
+                            close(inet);
+                            cleanup();
+                            exit(1);
+                        }
+                    }
 
-									memset(&a_ifr, 0, sizeof(a_ifr));
-									memset(&addr, 0, sizeof(addr));
-									memset(&snm, 0, sizeof(addr));
-									strncpy(a_ifr.ifr_name, ifr.ifr_name, IFNAMSIZ);
-									addr.sin_family = AF_INET;
-									snm.sin_family = AF_INET;
+                    // Configure ARP characteristics
+                    char path_buf[256];
+                    if (device_type == IF_TAP) {
+                        snprintf(path_buf, sizeof(path_buf), "/proc/sys/net/ipv4/neigh/%s/base_reachable_time_ms", ifr.ifr_name);
+                        int arp_fd = open(path_buf, O_WRONLY);
+                        if (arp_fd < 0) {
+                            perror("Could not open proc entry for ARP parameters");
+                            close(inet);
+                            cleanup();
+                            exit(1);
+                        } else {
+                            if (dprintf(arp_fd, "%d", ARP_BASE_REACHABLE_TIME*1000) <= 0) {
+                                perror("Could not configure interface ARP parameter base_reachable_time_ms");
+                                close(inet);
+                                close(arp_fd);
+                                cleanup();
+                                exit(1);
+                            } else {
+                                close(arp_fd);
+                            }
+                        }
 
-									int addr_conversion = inet_pton(AF_INET, ipv4_addr, &(addr.sin_addr));
-									if (addr_conversion != 1) {
-										printf("Error: Invalid IPv4 address specified\r\n");
-										close(inet);
-										cleanup();
-										exit(1);
-									} else {
-										a_ifr.ifr_addr = *(struct sockaddr*)&addr;
-										if (ioctl(inet, SIOCSIFADDR, &a_ifr) < 0) {
-											perror("Could not set IP-address");
-											close(inet);
-											cleanup();
-											exit(1);
-										} else {
-											if (set_netmask) {
-												int snm_conversion = inet_pton(AF_INET, netmask, &(snm.sin_addr));
-												if (snm_conversion != 1) {
-													printf("Error: Invalid subnet mask specified\r\n");
-													close(inet);
-													cleanup();
-													exit(1);
-												} else {
-													a_ifr.ifr_addr = *(struct sockaddr*)&snm;
-													if (ioctl(inet, SIOCSIFNETMASK, &a_ifr) < 0) {
-														perror("Could not set subnet mask");
-														close(inet);
-														cleanup();
-														exit(1);
-													}
-												}
-											}
-										}
-									}
-								}
-							}
-						}
-					}
-				}
-			}
+                        snprintf(path_buf, sizeof(path_buf), "/proc/sys/net/ipv4/neigh/%s/retrans_time_ms", ifr.ifr_name);
+                        arp_fd = open(path_buf, O_WRONLY);
+                        if (arp_fd < 0) {
+                            perror("Could not open proc entry for ARP parameters");
+                            close(inet);
+                            cleanup();
+                            exit(1);
+                        } else {
+                            if (dprintf(arp_fd, "%d", ARP_RETRANS_TIME*1000) <= 0) {
+                                perror("Could not configure interface ARP parameter retrans_time_ms");
+                                close(inet);
+                                close(arp_fd);
+                                cleanup();
+                                exit(1);
+                            } else {
+                                close(arp_fd);
+                            }
+                        }
+                    }
 
-			return fd;
-		}
-	}
+                    // Bring up if requested
+                    if (!noup) {
+                        if (ioctl(inet, SIOCGIFFLAGS, &ifr) < 0) {
+                            perror("Could not get interface flags from kernel");
+                            close(inet);
+                            cleanup();
+                            exit(1);
+                        } else {
+                            ifr.ifr_flags |= IFF_UP | IFF_RUNNING;
+                            if (ioctl(inet, SIOCSIFFLAGS, &ifr) < 0) {
+                                perror("Could not bring up interface");
+                                close(inet);
+                                cleanup();
+                                exit(1);
+                            } else {
+                                if (set_ipv4) {
+                                    struct ifreq a_ifr;
+                                    struct sockaddr_in addr, snm;
+
+                                    memset(&a_ifr, 0, sizeof(a_ifr));
+                                    memset(&addr, 0, sizeof(addr));
+                                    memset(&snm, 0, sizeof(addr));
+                                    strncpy(a_ifr.ifr_name, ifr.ifr_name, IFNAMSIZ);
+                                    addr.sin_family = AF_INET;
+                                    snm.sin_family = AF_INET;
+
+                                    int addr_conversion = inet_pton(AF_INET, ipv4_addr, &(addr.sin_addr));
+                                    if (addr_conversion != 1) {
+                                        printf("Error: Invalid IPv4 address specified\r\n");
+                                        close(inet);
+                                        cleanup();
+                                        exit(1);
+                                    } else {
+                                        a_ifr.ifr_addr = *(struct sockaddr*)&addr;
+                                        if (ioctl(inet, SIOCSIFADDR, &a_ifr) < 0) {
+                                            perror("Could not set IP-address");
+                                            close(inet);
+                                            cleanup();
+                                            exit(1);
+                                        } else {
+                                            if (set_netmask) {
+                                                int snm_conversion = inet_pton(AF_INET, netmask, &(snm.sin_addr));
+                                                if (snm_conversion != 1) {
+                                                    printf("Error: Invalid subnet mask specified\r\n");
+                                                    close(inet);
+                                                    cleanup();
+                                                    exit(1);
+                                                } else {
+                                                    a_ifr.ifr_addr = *(struct sockaddr*)&snm;
+                                                    if (ioctl(inet, SIOCSIFNETMASK, &a_ifr) < 0) {
+                                                        perror("Could not set subnet mask");
+                                                        close(inet);
+                                                        cleanup();
+                                                        exit(1);
+                                                    }
+                                                }
+                                            }
+                                        }
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+
+            return fd;
+        }
+    }
 }
 
 int close_tap(int tap_fd) {
-	return close(tap_fd);
+    return close(tap_fd);
 }

TCP.c

@@ -0,0 +1,37 @@
+#include "TCP.h"
+
+int open_tcp(char* ip, int port) {
+    int sockfd = socket(AF_INET, SOCK_STREAM, 0);
+
+    if (sockfd < 0) {
+        perror("Could not open AF_INET socket");
+        exit(1);
+    }
+
+    struct hostent *server;
+    struct sockaddr_in serv_addr;
+
+    server = gethostbyname(ip);
+
+    if (server == NULL) {
+        perror("Error resolving host");
+        exit(1);
+    }
+
+    memset(&serv_addr, 0, sizeof(serv_addr)); 
+    serv_addr.sin_family = AF_INET;
+
+    memcpy(server->h_addr, &serv_addr.sin_addr.s_addr, server->h_length);
+    serv_addr.sin_port = htons(port);
+
+    if (connect(sockfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) < 0) {
+        perror("Could not connect TCP socket");
+        exit(1);
+    }
+
+    return sockfd;
+}
+
+int close_tcp(int fd) {
+    return close(fd);
+}

TCP.h

@@ -0,0 +1,9 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+#include <unistd.h>
+#include <netdb.h>
+
+int open_tcp(char* ip, int port);
+int close_tcp(int fd);

makefile

@@ -1,26 +1,35 @@
 .DEFAULT_GOAL := all
 .PHONY: all clean install uninstall tncattach
 
-compiler = gcc
-flags = -std=gnu11 -lm
+RM ?= rm
+INSTALL ?= install
+CC ?= gcc
+CFLAGS ?= -Wall -std=gnu11 -static-libgcc
+LDFLAGS ?= 
+PREFIX ?= /usr/local
 
 all: tncattach
 rebuild: clean all
 
 clean:
 	@echo "Cleaning tncattach build..."
-	@rm -f tncattach
+	$(RM) -f tncattach
 
 tncattach:
 	@echo "Making tncattach..."
-	@echo "Compiling with: ${compiler}"
-	${compiler} ${flags} tncattach.c Serial.c KISS.c TAP.c -o tncattach -Wall
+	@echo "Compiling with: $(CC)"
+	$(CC) $(CFLAGS) $(LDFLAGS) tncattach.c Serial.c TCP.c KISS.c TAP.c -o tncattach
 
 install:
 	@echo "Installing tncattach..."
-	chmod a+x tncattach
-	cp ./tncattach /usr/local/sbin/
+	$(INSTALL) -d $(DESTDIR)/$(PREFIX)/bin
+	$(INSTALL) -Dm755 tncattach $(DESTDIR)/$(PREFIX)/bin/tncattach
+	@echo "Installing man page..."
+	gzip -9 tncattach.8
+	$(INSTALL) -d $(DESTDIR)/$(PREFIX)/share/man/man8
+	$(INSTALL) -Dm644 tncattach.8.gz $(DESTDIR)/$(PREFIX)/share/man/man8/tncattach.8.gz
 
 uninstall:
 	@echo "Uninstalling tncattach"
-	rm /usr/local/sbin/tncattach
+	$(RM) $(DESTDIR)/$(PREFIX)/bin/tncattach
+	$(RM) $(DESTDIR)/$(PREFIX)/share/man/man8/tncattach.8.gz

tncattach.8

@@ -0,0 +1,165 @@
+.TH tncattach 8 "September 12, 2020"
+
+.SH NAME
+.
+.
+tncattach \- Attach TNC devices as system network interfaces
+
+.SH SYNOPSIS
+.
+.
+\f[B]tncattach\f[R] [OPTION...] port baudrate
+
+.SH DESCRIPTION
+Attach KISS TNC devices as network interfaces in Linux. This program allows you to attach TNCs or any KISS-compatible device as a network interface. This program does not need any kernel modules, and has no external dependencies outside the standard Linux and GNU C libraries.
+
+.SH OPTIONS
+.
+.
+.TP
+.BI \-m, \-\-mtu=MTU
+.
+Specify interface MTU
+.
+.
+.TP
+.BI \-e, \-\-ethernet
+Create a full ethernet device
+.
+.
+.TP
+.BI \-i, \-\-ipv4=IP_ADDRESS
+Configure an IPv4 address on interface
+.
+.
+.TP
+.BI \-n, \-\-noipv6
+Filter IPv6 traffic from reaching TNC
+.
+.
+.TP
+.BI \-\-noup
+Only create interface, don't bring it up
+.
+.
+.TP
+.BI \-T, \-\-kisstcp
+Use KISS over TCP instead of serial port
+.
+.
+.TP
+.BI \-H, \-\-tcphost=TCP_HOST
+Host to connect to when using KISS over TCP
+.
+.
+.TP
+.BI \-P, \-\-tcpport=TCP_PORT
+TCP port when using KISS over TCP
+.
+.
+.TP
+.BI \-t, \-\-interval=SECONDS
+Maximum interval between station identifications
+.
+.
+.TP
+.B \-s, \-\-id=CALLSIGN
+Station identification data
+.
+.
+.TP
+.BI \-d, \-\-daemon
+Run tncattach as a daemon
+.
+.
+.TP
+.BI \-v, \-\-verbose
+Enable verbose output
+.
+.
+.TP
+.BI \-?, \-\-help
+Show help
+.
+.
+.TP
+.BI \-\-usage
+Give a short usage message
+.
+.
+.TP
+.BI \-V, \-\-version
+Print program version
+.
+.
+
+.SH USAGE
+The program supports attaching TNCs as point-to-point tunnel devices, or generic ethernet devices. The ethernet mode is suitable for point-to-multipoint setups, and can be enabled with the corresponding command line switch. If you only need point-to-point links, it is advisable to just use the standard point-to-point mode, since it doesn't incur the ethernet header overhead on each packet.
+.P
+If you want to connect to a virtual KISS TNC over a TCP connection, you can use the -T option, along with the -H and -P options to specify the host and port.
+.P
+Additionally, it is worth noting that tncattach can filter out IPv6 packets from reaching the TNC. Most operating systems attempts to autoconfigure IPv6 when an interface is brought up, which results in a substantial amount of IPv6 traffic generated by router solicitations and similar, which is usually unwanted for packet radio links and similar.
+.P
+If you intend to use tncattach on a system with mDNS services enabled (avahi-daemon, for example), you may want to consider modifying your mDNS setup to exclude TNC interfaces, or turning it off entirely, since it will generate a lot of traffic that might be unwanted.
+
+.SH STATION IDENTIFICATION
+
+You can configure tncattach to automatically transmit station identification beacons according to a given interval, by using the --id and --interval options. Identification will be transmitted as raw data frames with whatever content has been specified in the --id option. Useful for amateur radio use, or other areas where station identification is necessary.
+.P
+Identification beacons will be transmitted when:
+.P
+.IP
+There is outgoing data to send, and the specified interval has elapsed.
+.IP
+The specified interval elapses, and data has been sent since the last ID beacon.
+.IP
+The program exits, if any data frames have been transmitted since the last ID beacon.
+.P
+The above methodology should comply with station identification rules for amateur radio in most parts of the world, and complies with US Part 97 rules.
+
+.SH EXAMPLES
+.
+Create an ethernet device with a USB-connected TNC, set the MTU, filter IPv6 traffic, and set an IPv4 address:
+.IP
+sudo tncattach /dev/ttyUSB0 115200 --ethernet --mtu 576 --noipv6 --ipv4 10.92.0.10/24
+.P
+Create an ethernet device with a TCP-connected TNC, set the MTU, filter IPv6 traffic, and set an IPv4 address:
+.IP
+sudo tncattach -T -H localhost -P 8001 --ethernet --mtu 576 --noipv6 --ipv4 10.92.0.10/24
+.P
+You can interact with the interface like any other using the ip or ifconfig utilities.
+.p
+Check interface is running:
+.P
+# ifconfig
+.br
+tnc0: flags=4305<UP,POINTOPOINT,RUNNING,NOARP,MULTICAST>  mtu 400
+.br
+        inet 10.93.0.1  netmask 255.255.255.255  destination 10.93.0.2
+.br
+        unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  txqueuelen 500  (UNSPEC)
+.br
+        RX packets 0  bytes 0 (0.0 B)
+.br
+        RX errors 0  dropped 0  overruns 0  frame 0
+.br
+        TX packets 0  bytes 0 (0.0 B)
+.br
+        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
+.P
+.SH WORTH KNOWING ON RASPBIAN
+On some versions of Raspbian (and probably other operating systems), the DHCP client daemon dhcpcd interferes with TNC interfaces, by overriding their MTU and trying to auto-configure link-local addresses. You probably don't want this, and it can be disabled by editing the /etc/dhcpcd.conf file, adding a statement telling dhcpcd to ignore your TNC interface:
+.P
+# Add the following statement somewhere at the beginning
+.br
+# of /etc/dhcpcd.conf to prevent dhcpcd from changing MTU
+.br
+denyinterfaces tnc0
+
+.SH SEE ALSO
+
+rnodeconfigutil(8)
+
+.SH AUTHOR
+
+Mark Qvist