From: Roy Marples <roy@marples.name>
Date: Tue, 8 Oct 2019 12:35:50 +0000 (+0100)
Subject: ARP: Don't send an initial ARP announcement for newly added addresses
X-Git-Tag: v8.1.0~15
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1c6064da648c9b67a79d7f2b9d19e91d17db2177;p=thirdparty%2Fdhcpcd.git

ARP: Don't send an initial ARP announcement for newly added addresses

The kernel will do this for us.
---

diff --git a/src/arp.c b/src/arp.c
index 33725211..55b6203b 100644
--- a/src/arp.c
+++ b/src/arp.c
@@ -425,6 +425,7 @@ arp_announce1(void *arg)
 {
 	struct arp_state *astate = arg;
 	struct interface *ifp = astate->iface;
+	struct ipv4_addr *ia;
 
 	if (++astate->claims < ANNOUNCE_NUM)
 		logdebugx("%s: ARP announcing %s (%d of %d), "
@@ -435,24 +436,26 @@ arp_announce1(void *arg)
 		logdebugx("%s: ARP announcing %s (%d of %d)",
 		    ifp->name, inet_ntoa(astate->addr),
 		    astate->claims, ANNOUNCE_NUM);
+
+	/* The kernel will send a Gratuitous ARP for newly added addresses.
+	 * So we can avoid sending the same. */
+	ia = ipv4_iffindaddr(ifp, &astate->addr, NULL);
+	if (astate->claims == 1 && ia != NULL && ia->flags & IPV4_AF_NEW)
+		goto skip_request;
+
 	if (arp_request(ifp, &astate->addr, &astate->addr) == -1)
 		logerr(__func__);
+
+skip_request:
+	/* No longer a new address. */
+	if (ia != NULL)
+		ia->flags |= ~IPV4_AF_NEW;
+
 	eloop_timeout_add_sec(ifp->ctx->eloop, ANNOUNCE_WAIT,
 	    astate->claims < ANNOUNCE_NUM ? arp_announce1 : arp_announced,
 	    astate);
 }
 
-/*
- * XXX FIXME
- * Kernels supporting RFC5227 will announce the address when it's
- * added.
- * dhcpcd should not announce when this happens, nor need to open
- * a BPF socket for it.
- * Also, an address might be added to a non preferred inteface when
- * the same address exists on a preferred one so we need to instruct
- * the kernel not to announce the address somehow.
- */
-
 void
 arp_announce(struct arp_state *astate)
 {
@@ -498,6 +501,9 @@ arp_ifannounceaddr(struct interface *ifp, const struct in_addr *ia)
 {
 	struct arp_state *astate;
 
+	if (ifp->flags & IFF_NOARP)
+		return;
+
 	astate = arp_find(ifp, ia);
 	if (astate == NULL) {
 		astate = arp_new(ifp, ia);
diff --git a/src/ipv4.c b/src/ipv4.c
index 8c89dc73..c55a7da6 100644
--- a/src/ipv4.c
+++ b/src/ipv4.c
@@ -622,7 +622,6 @@ ipv4_addaddr(struct interface *ifp, const struct in_addr *addr,
 {
 	struct ipv4_state *state;
 	struct ipv4_addr *ia;
-	bool is_new = false;
 #ifdef ALIAS_ADDR
 	int replaced, blank;
 	struct ipv4_addr *replaced_ia;
@@ -653,8 +652,9 @@ ipv4_addaddr(struct interface *ifp, const struct in_addr *addr,
 #ifdef IN_IFF_TENTATIVE
 		ia->addr_flags = IN_IFF_TENTATIVE;
 #endif
-		is_new = true;
-	}
+		ia->flags = IPV4_AF_NEW;
+	} else
+		ia->flags |= ~IPV4_AF_NEW;
 
 	ia->mask = *mask;
 	ia->brd = *bcast;
@@ -698,7 +698,7 @@ ipv4_addaddr(struct interface *ifp, const struct in_addr *addr,
 	}
 #endif
 
-	if (is_new)
+	if (ia->flags & IPV4_AF_NEW)
 		TAILQ_INSERT_TAIL(&state->addrs, ia, next);
 	return ia;
 }
@@ -743,8 +743,7 @@ ipv4_applyaddr(void *arg)
 #ifdef ARP
 				/* Announce the preferred address to
 				 * kick ARP caches. */
-				if (!(ifp->flags & IFF_NOARP))
-					arp_announceaddr(ifp->ctx,&lease->addr);
+				arp_announceaddr(ifp->ctx,&lease->addr);
 #endif
 			}
 			script_runreason(ifp, state->reason);
@@ -806,8 +805,7 @@ ipv4_applyaddr(void *arg)
 	rt_build(ifp->ctx, AF_INET);
 
 #ifdef ARP
-	if (!(ifp->flags & IFF_NOARP))
-		arp_announceaddr(ifp->ctx, &state->addr->addr);
+	arp_announceaddr(ifp->ctx, &state->addr->addr);
 #endif
 
 	if (state->state == DHS_BOUND) {
diff --git a/src/ipv4.h b/src/ipv4.h
index eaa0dcce..59b48a53 100644
--- a/src/ipv4.h
+++ b/src/ipv4.h
@@ -100,6 +100,7 @@ struct ipv4_addr {
 TAILQ_HEAD(ipv4_addrhead, ipv4_addr);
 
 #define	IPV4_AF_STALE		(1U << 0)
+#define	IPV4_AF_NEW		(1U << 1)
 
 #define	IPV4_ADDR_EQ(a1, a2)	((a1) && (a1)->addr.s_addr == (a2)->addr.s_addr)
 #define	IPV4_MASK1_EQ(a1, a2)	((a1) && (a1)->mask.s_addr == (a2)->mask.s_addr)