From 30207d6691e04eab5071aa68a0be441913688a03 Mon Sep 17 00:00:00 2001
From: Mark Qvist <mark@adepta.io>
Date: Mon, 1 Jun 2020 22:54:15 +0200
Subject: [PATCH] Added ARP configuration for interface

---
 Constants.h |  6 +++++-
 TAP.c       | 43 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/Constants.h b/Constants.h
index cd9e3a2..fd366ee 100644
--- a/Constants.h
+++ b/Constants.h
@@ -8,4 +8,8 @@
 #define MTU_MAX 1522
 #define MTU_DEFAULT 329
 
-#define TXQUEUELEN 10
\ No newline at end of file
+#define TXQUEUELEN 10
+
+// ARP timings, in seconds
+#define ARP_BASE_REACHABLE_TIME 300
+#define ARP_RETRANS_TIME 5
\ No newline at end of file
diff --git a/TAP.c b/TAP.c
index c2be769..45f5d00 100644
--- a/TAP.c
+++ b/TAP.c
@@ -80,6 +80,49 @@ int open_tap(void) {
 						}
 					}
 
+					// 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);
+							}
+						}
+
+						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);
+							}
+						}
+					}
+
+					// Bring up if requested
 					if (!noup) {
 						if (ioctl(inet, SIOCGIFFLAGS, &ifr) < 0) {
 							perror("Could not get interface flags from kernel");