diff --git a/src/client.cpp b/src/client.cpp
index d404769..17fbe51 100644
--- a/src/client.cpp
+++ b/src/client.cpp
@@ -519,10 +519,8 @@ ContextImpl::ContextImpl(const Config& conf, const evbase& tcp_loop)
             log_err_printf(setup, "%s  Ignoring %s\n", e.what(), addr.c_str());
             continue;
         }
-        auto top = ntohl(saddr->in.sin_addr.s_addr)>>24u;
-        auto ismcast = top>224 && top<239;
-        bool isbcast = bcasts.find(saddr)!=bcasts.end();
-        auto isucast = !isbcast && !ismcast;
+        // if !bcast and !mcast
+        auto isucast = bcasts.find(saddr)==bcasts.end() && !saddr.isMCast();
 
         log_info_printf(io, "Searching to %s%s\n", saddr.tostring().c_str(), (isucast?" unicast":""));
         searchDest.emplace_back(saddr, isucast);
diff --git a/src/osiSockExt.h b/src/osiSockExt.h
index 5fb34f7..b39b3d0 100644
--- a/src/osiSockExt.h
+++ b/src/osiSockExt.h
@@ -44,6 +44,8 @@ public:
     inline explicit SockAddr(int af, const std::string& address) :SockAddr(af, address.c_str()) {}
 
     size_t size() const;
+    inline
+    size_t capacity() const { return sizeof(store); }
 
     inline unsigned short family() const { return store.sa.sa_family; }
     unsigned short port() const;
@@ -58,6 +60,7 @@ public:
 
     bool isAny() const;
     bool isLO() const;
+    bool isMCast() const;
 
     store_t* operator->() { return &store; }
     const store_t* operator->() const { return &store; }
diff --git a/src/util.cpp b/src/util.cpp
index 18ad8a3..48704da 100644
--- a/src/util.cpp
+++ b/src/util.cpp
@@ -350,6 +350,17 @@ bool SockAddr::isLO() const
     }
 }
 
+bool SockAddr::isMCast() const
+{
+    switch(store.sa.sa_family) {
+    case AF_INET: return IN_MULTICAST(store.in.sin_addr.s_addr);
+#ifdef AF_INET6
+    case AF_INET6: return IN6_IS_ADDR_MULTICAST(&store.in6.sin6_addr);
+#endif
+    default: return false;
+    }
+}
+
 std::string SockAddr::tostring() const
 {
     std::ostringstream strm;