2 files changed, 3 insertions, 2 deletions
diff --git a/lib/ip.c b/lib/ip.c
index b940bf5..0afe979 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 49aa13a..4c4fab9 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)