Send periodic ARP requests when ARP entries for hosts we are sending

to are about to expire.  This prevents high packet rate flows from
experiencing packet drops at the sender following ARP cache entry
timeout.

PR:		kern/25517
Reviewed by:	luigi
MFC after:	7 days

1 files changed, 15 insertions, 0 deletions

diff --git a/sys/netinet/if_ether.c b/sys/netinet/if_ether.c
index 68b2221..1bd85a3 100644
--- a/sys/netinet/if_ether.c
+++ b/sys/netinet/if_ether.c
@@ -427,6 +427,21 @@ arpresolve(ifp, rt, m, dst, desten, rt0)
 	 */
 	if ((rt->rt_expire == 0 || rt->rt_expire > time_second) &&
 	    sdl->sdl_family == AF_LINK && sdl->sdl_alen != 0) {
+		/*
+		 * If entry has an expiry time and it is approaching,
+		 * see if we need to send an ARP request within this
+		 * arpt_down interval.
+		 */
+		if ((rt->rt_expire != 0) &&
+		    (time_second + (arp_maxtries - la->la_asked) * arpt_down >
+		     rt->rt_expire)) {
+			arprequest(ifp,
+				   &SIN(rt->rt_ifa->ifa_addr)->sin_addr,
+				   &SIN(dst)->sin_addr,
+				   IF_LLADDR(ifp));
+			la->la_asked++;
+		} 
+
 		bcopy(LLADDR(sdl), desten, sdl->sdl_alen);
 		return 1;
 	}