From 73ce7b01b4496a5fbf9caf63033c874be692333f Mon Sep 17 00:00:00 2001 From: Denys Fedoryshchenko Date: Fri, 13 Mar 2009 16:02:07 -0700 Subject: [PATCH] ipv4: arp announce, arp_proxy and windows ip conflict verification Windows (XP at least) hosts on boot, with configured static ip, performing address conflict detection, which is defined in RFC3927. Here is quote of important information: " An ARP announcement is identical to the ARP Probe described above, except that now the sender and target IP addresses are both set to the host's newly selected IPv4 address. " But it same time this goes wrong with RFC5227. " The 'sender IP address' field MUST be set to all zeroes; this is to avoid polluting ARP caches in other hosts on the same link in the case where the address turns out to be already in use by another host. " When ARP proxy configured, it must not answer to both cases, because it is address conflict verification in any case. For Windows it is just causing to detect false "ip conflict". Already there is code for RFC5227, so just trivially we just check also if source ip == target ip. Signed-off-by: Denys Fedoryshchenko Signed-off-by: David S. Miller --- net/ipv4/arp.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c index 9c220323f35..f11931c1838 100644 --- a/net/ipv4/arp.c +++ b/net/ipv4/arp.c @@ -801,8 +801,11 @@ static int arp_process(struct sk_buff *skb) * cache. */ - /* Special case: IPv4 duplicate address detection packet (RFC2131) */ - if (sip == 0) { + /* + * Special case: IPv4 duplicate address detection packet (RFC2131) + * and Gratuitous ARP/ARP Announce. (RFC3927, Section 2.4) + */ + if (sip == 0 || tip == sip) { if (arp->ar_op == htons(ARPOP_REQUEST) && inet_addr_type(net, tip) == RTN_LOCAL && !arp_ignore(in_dev, sip, tip)) -- 2.20.1