I will hold off on committing this pending further feedback.
Regards,
BMS
This patch forces the FreeBSD IPv4 ARP code to broadcast ARP replies
for IPv4 link-local addresses, as required by RFC 3927, if and only
if the request was destined for the local machine (ie not proxied).
The code does not set ar_tha by itself; it relies on the AF_ARP handler
in net/if_ethersubr.c to set it to if_broadaddr for us.
Delta 1.97-1.98 of netinet/in.h is required for the IN_LINKLOCAL() macro.
Index: if_ether.c
===================================================================
RCS file: /home/ncvs/src/sys/netinet/if_ether.c,v
retrieving revision 1.158
diff -u -p -r1.158 if_ether.c
--- if_ether.c 14 Jan 2007 18:44:17 -0000 1.158
+++ if_ether.c 31 Jan 2007 14:35:48 -0000
@@ -885,11 +885,23 @@ reply:
}
}
+ if (itaddr.s_addr == myaddr.s_addr &&
+ IN_LINKLOCAL(ntohl(itaddr.s_addr))) {
+ /* RFC 3927 link-local IPv4; always reply by broadcast. */
+#ifdef DEBUG_LINKLOCAL
+ printf("arp: sending reply for link-local addr %s\n",
+ inet_ntoa(itaddr));
+#endif
+ m->m_flags |= M_BCAST;
+ m->m_flags &= ~M_MCAST;
+ } else {
+ /* default behaviour; never reply by broadcast. */
+ m->m_flags &= ~(M_BCAST|M_MCAST);
+ }
(void)memcpy(ar_tpa(ah), ar_spa(ah), ah->ar_pln);
(void)memcpy(ar_spa(ah), &itaddr, ah->ar_pln);
ah->ar_op = htons(ARPOP_REPLY);
ah->ar_pro = htons(ETHERTYPE_IP); /* let's be sure! */
- m->m_flags &= ~(M_BCAST|M_MCAST); /* never reply by broadcast */
m->m_len = sizeof(*ah) + (2 * ah->ar_pln) + (2 * ah->ar_hln);
m->m_pkthdr.len = m->m_len;
sa.sa_family = AF_ARP;
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