ipv4: allow warming up the ARP cache with request type gratuitous ARP

If the per device ARP_ACCEPT option is enable, currently we only allow
creating new ARP cache entries for response type gratuitous ARP.

Allowing gratuitous ARP to create new ARP entries (not only to update
existing ones) is useful when we want to avoid unnecessary delays for
the first packet of a stream.

This patch allows request type gratuitous ARP to create new ARP cache
entries as well. This is useful when we want to populate the ARP cache
entries for a large number of hosts on the same LAN.

Signed-off-by: Octavian Purdila <opurdila@ixiacom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 14 insertions, 4 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index c532884f4fec..2dc7a1d97686 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -852,9 +852,18 @@ arp_notify - BOOLEAN
             or hardware address changes.
 
 arp_accept - BOOLEAN
-        Define behavior when gratuitous arp replies are received:
-        0 - drop gratuitous arp frames
-        1 - accept gratuitous arp frames
+        Define behavior for gratuitous ARP frames who's IP is not
+        already present in the ARP table:
+        0 - don't create new entries in the ARP table
+        1 - create new entries in the ARP table
+
+        Both replies and requests type gratuitous arp will trigger the
+        ARP table to be updated, if this setting is on.
+
+        If the ARP table already contains the IP address of the
+        gratuitous arp frame, the arp table will be updated regardless
+        if this setting is on or off.
+
 
 app_solicit - INTEGER
         The maximum number of probes to send to the user space ARP daemon
diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index 078709233bc4..1940b4df7699 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -907,7 +907,8 @@ static int arp_process(struct sk_buff *skb)
                    devices (strip is candidate)
                  */
                 if (n == NULL &&
-                    arp->ar_op == htons(ARPOP_REPLY) &&
+                    (arp->ar_op == htons(ARPOP_REPLY) ||
+                     (arp->ar_op == htons(ARPOP_REQUEST) && tip == sip)) &&
                     inet_addr_type(net, sip) == RTN_UNICAST)
                         n = __neigh_lookup(&arp_tbl, &sip, dev, 1);
         }