Fix behavior of ipa_opposite().

It was giving wrong results on /30 networks.

4 files changed, 5 insertions, 4 deletions

diff --git a/lib/ip.c b/lib/ip.c
index b940bf53..0afe9796 100644
--- a/lib/ip.c
+++ b/lib/ip.c
@@ -153,13 +153,14 @@ int ipa_classify(ip_addr x) { DUMMY }
 /**
  * ipa_opposite - return address of point-to-point neighbor
  * @x: IP address of our end of the link
+ * @pxlen: network prefix length
  *
  * ipa_opposite() returns an address of the opposite end of a numbered
  * point-to-point link.
  *
  * This function is available in IPv4 version only.
  */
-ip_addr ipa_opposite(ip_addr x) { DUMMY }
+ip_addr ipa_opposite(ip_addr x, int pxlen) { DUMMY }
 
 /**
  * ipa_class_mask - guess netmask according to address class
diff --git a/lib/ipv4.h b/lib/ipv4.h
index 49aa13a6..4c4fab90 100644
--- a/lib/ipv4.h
+++ b/lib/ipv4.h
@@ -53,7 +53,7 @@ typedef u32 ip_addr;
 #define ipa_hton(x) x = _MI(htonl(_I(x)))
 #define ipa_ntoh(x) x = _MI(ntohl(_I(x)))
 #define ipa_classify(x) ipv4_classify(_I(x))
-#define ipa_opposite(x) _MI(_I(x) ^ 1)
+#define ipa_opposite(x,len) _MI(_I(x) ^ (len == 30 ? 3 : 1))
 #define ipa_class_mask(x) _MI(ipv4_class_mask(_I(x)))
 #define ipa_from_u32(x) _MI(x)
 #define ipa_to_u32(x) _I(x)
diff --git a/sysdep/linux/netlink/netlink.c b/sysdep/linux/netlink/netlink.c
index a54e1157..a70428ef 100644
--- a/sysdep/linux/netlink/netlink.c
+++ b/sysdep/linux/netlink/netlink.c
@@ -377,7 +377,7 @@ nl_parse_addr(struct nlmsghdr *h)
       ifa.brd = ipa_or(ifa.ip, ipa_not(netmask));
 #ifndef IPV6
       if (i->ifa_prefixlen == BITS_PER_IP_ADDRESS - 2)
-	ifa.opposite = ipa_opposite(ifa.ip);
+	ifa.opposite = ipa_opposite(ifa.ip, i->ifa_prefixlen);
       if ((ifi->flags & IF_BROADCAST) && a[IFA_BROADCAST])
 	{
 	  memcpy(&xbrd, RTA_DATA(a[IFA_BROADCAST]), sizeof(xbrd));
diff --git a/sysdep/unix/krt-iface.c b/sysdep/unix/krt-iface.c
index 5cc78807..37f9d0bd 100644
--- a/sysdep/unix/krt-iface.c
+++ b/sysdep/unix/krt-iface.c
@@ -140,7 +140,7 @@ scan_ifs(struct ifreq *r, int cnt)
 	  if (a.pxlen < 30)
 	    i.flags |= IF_MULTIACCESS;
 	  else
-	    a.opposite = ipa_opposite(a.ip);
+	    a.opposite = ipa_opposite(a.ip, a.pxlen);
 	}
       else
 	a.brd = a.opposite;