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+<a id="tor-spec.txt-6.4"></a>
+
+# Remote hostname lookup
+
+To find the address associated with a hostname, the OP sends a
+RELAY_RESOLVE message containing the hostname to be resolved with a NUL
+terminating byte. (For a reverse lookup, the OP sends a RELAY_RESOLVE
+message containing an in-addr.arpa address.) The OR replies with a
+RELAY_RESOLVED message containing any number of answers. Each answer is
+of the form:
+
+```text
+       Type   (1 octet)
+       Length (1 octet)
+       Value  (variable-width)
+       TTL    (4 octets)
+   "Length" is the length of the Value field.
+   "Type" is one of:
+
+      0x00 -- Hostname
+      0x04 -- IPv4 address
+      0x06 -- IPv6 address
+      0xF0 -- Error, transient
+      0xF1 -- Error, nontransient
+
+    If any answer has a type of 'Error', then no other answer may be
+    given.
+
+    The 'Value' field encodes the answer:
+        IP addresses are given in network order.
+        Hostnames are given in standard DNS order ("www.example.com")
+          and not NUL-terminated.
+        The content of Errors is currently ignored. Relays currently
+          set it to the string "Error resolving hostname" with no
+          terminating NUL. Implementations MUST ignore this value.
+
+    For backward compatibility, if there are any IPv4 answers, one of those
+    must be given as the first answer.
+
+    The RELAY_RESOLVE messge must use a nonzero, distinct streamID; the
+    corresponding RELAY_RESOLVED message must use the same streamID.  No stream
+    is actually created by the OR when resolving the name.
+```