isisd: don't require IPv4 for adjacency

This was precluding isisd from IPv6-only operation; no adjacency would
come up unless there was IPv4 in parallel.

Reported-by: Martin Winter <mwinter@netdef.org>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>

isisd/isis_pdu.c

@@ -402,6 +402,7 @@ process_p2p_hello (struct isis_circuit *circuit)
   u_int32_t expected = 0, found = 0, auth_tlv_offset = 0;
   uint16_t pdu_len;
   struct tlvs tlvs;
+  int v4_usable = 0, v6_usable = 0;
 
   if (isis->debugs & DEBUG_ADJ_PACKETS)
     {
@@ -518,11 +519,44 @@ process_p2p_hello (struct isis_circuit *circuit)
   /*
    * check if it's own interface ip match iih ip addrs
    */
-  if ((found & TLVFLAG_IPV4_ADDR) == 0 ||
-      ip_match (circuit->ip_addrs, tlvs.ipv4_addrs) == 0)
+  if (found & TLVFLAG_IPV4_ADDR)
+    {
+      if (ip_match (circuit->ip_addrs, tlvs.ipv4_addrs))
+	v4_usable = 1;
+      else
+	zlog_warn ("ISIS-Adj: IPv4 addresses present but no overlap "
+		   "in P2P IIH from %s\n", circuit->interface->name);
+    }
+#ifndef HAVE_IPV6
+  else /* !(found & TLVFLAG_IPV4_ADDR) */
+    zlog_warn ("ISIS-Adj: no IPv4 in P2P IIH from %s "
+	       "(this isisd has no IPv6)\n", circuit->interface->name);
+
+#else
+  if (found & TLVFLAG_IPV6_ADDR)
+    {
+      /* TBA: check that we have a linklocal ourselves? */
+      struct listnode *node;
+      struct prefix_ipv6 *ip;
+      for (ALL_LIST_ELEMENTS_RO (tlvs.ipv6_addrs, node, ip))
+	if (IN6_IS_ADDR_LINKLOCAL (ip))
+	  {
+	    v6_usable = 1;
+	    break;
+	  }
+
+      if (!v6_usable)
+	zlog_warn ("ISIS-Adj: IPv6 addresses present but no link-local "
+		   "in P2P IIH from %s\n", circuit->interface->name);
+    }
+
+  if (!(found & (TLVFLAG_IPV4_ADDR | TLVFLAG_IPV6_ADDR)))
+    zlog_warn ("ISIS-Adj: neither IPv4 nor IPv6 addr in P2P IIH from %s\n",
+	       circuit->interface->name);
+#endif
+
+  if (!v6_usable && !v4_usable)
     {
-      zlog_warn ("ISIS-Adj: No usable IP interface addresses "
-                 "in LAN IIH from %s\n", circuit->interface->name);
       free_tlvs (&tlvs);
       return ISIS_WARNING;
     }
@@ -859,6 +893,7 @@ process_lan_hello (int level, struct isis_circuit *circuit, u_char * ssnpa)
   struct tlvs tlvs;
   u_char *snpa;
   struct listnode *node;
+  int v4_usable = 0, v6_usable = 0;
 
   if (isis->debugs & DEBUG_ADJ_PACKETS)
     {
@@ -1045,15 +1080,49 @@ process_lan_hello (int level, struct isis_circuit *circuit, u_char * ssnpa)
   /*
    * check if it's own interface ip match iih ip addrs
    */
-  if ((found & TLVFLAG_IPV4_ADDR) == 0 ||
-      ip_match (circuit->ip_addrs, tlvs.ipv4_addrs) == 0)
+  if (found & TLVFLAG_IPV4_ADDR)
     {
-      zlog_debug ("ISIS-Adj: No usable IP interface addresses "
-                  "in LAN IIH from %s\n", circuit->interface->name);
-      retval = ISIS_WARNING;
-      goto out;
+      if (ip_match (circuit->ip_addrs, tlvs.ipv4_addrs))
+	v4_usable = 1;
+      else
+	zlog_warn ("ISIS-Adj: IPv4 addresses present but no overlap "
+		   "in LAN IIH from %s\n", circuit->interface->name);
+    }
+#ifndef HAVE_IPV6
+  else /* !(found & TLVFLAG_IPV4_ADDR) */
+    zlog_warn ("ISIS-Adj: no IPv4 in LAN IIH from %s "
+	       "(this isisd has no IPv6)\n", circuit->interface->name);
+
+#else
+  if (found & TLVFLAG_IPV6_ADDR)
+    {
+      /* TBA: check that we have a linklocal ourselves? */
+      struct listnode *node;
+      struct prefix_ipv6 *ip;
+      for (ALL_LIST_ELEMENTS_RO (tlvs.ipv6_addrs, node, ip))
+	if (IN6_IS_ADDR_LINKLOCAL (ip))
+	  {
+	    v6_usable = 1;
+	    break;
+	  }
+
+      if (!v6_usable)
+	zlog_warn ("ISIS-Adj: IPv6 addresses present but no link-local "
+		   "in LAN IIH from %s\n", circuit->interface->name);
     }
 
+  if (!(found & (TLVFLAG_IPV4_ADDR | TLVFLAG_IPV6_ADDR)))
+    zlog_warn ("ISIS-Adj: neither IPv4 nor IPv6 addr in LAN IIH from %s\n",
+	       circuit->interface->name);
+#endif
+
+  if (!v6_usable && !v4_usable)
+    {
+      free_tlvs (&tlvs);
+      return ISIS_WARNING;
+    }
+
+
   adj = isis_adj_lookup (hdr.source_id, circuit->u.bc.adjdb[level - 1]);
   if ((adj == NULL) || (memcmp(adj->snpa, ssnpa, ETH_ALEN)) ||
       (adj->level != level))