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net: Correct check for link-local target IP conflict 

Make the link-local code conform more completely with the RFC.

This will prevent ARP queries for the target (such as while it is
rebooting) from causing the device to choose a different link-local
address, thinking that its address is in use by another machine.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
This commit is contained in:
Joe Hershberger 2013-02-08 14:18:53 -06:00
parent 62d7dba7be
commit 5da7cf81c8
1 changed files with 13 additions and 4 deletions
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17
net/link_local.c
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@ -206,6 +206,7 @@ void link_local_receive_arp(struct arp_hdr *arp, int len)
{ {
int source_ip_conflict; int source_ip_conflict;
int target_ip_conflict; int target_ip_conflict;
IPaddr_t null_ip = 0;
if (state == DISABLED) if (state == DISABLED)
return; return;
@ -267,10 +268,18 @@ void link_local_receive_arp(struct arp_hdr *arp, int len)
) { ) {
source_ip_conflict = 1; source_ip_conflict = 1;
} }
if (arp->ar_op == htons(ARPOP_REQUEST)
&& memcmp(&arp->ar_tpa, &ip, ARP_PLEN) == 0 /*
&& memcmp(&arp->ar_tha, NetOurEther, ARP_HLEN) != 0 * According to RFC 3927, section 2.2.1:
) { * Check if packet is an ARP probe by checking for a null source IP
* then check that target IP is equal to ours and source hw addr
* is not equal to ours. This condition should cause a conflict only
* during probe.
*/
if (arp->ar_op == htons(ARPOP_REQUEST) &&
memcmp(&arp->ar_spa, &null_ip, ARP_PLEN) == 0 &&
memcmp(&arp->ar_tpa, &ip, ARP_PLEN) == 0 &&
memcmp(&arp->ar_sha, NetOurEther, ARP_HLEN) != 0) {
target_ip_conflict = 1; target_ip_conflict = 1;
} }