[#1695] updated documentation

doc/sphinx/arm/dhcp4-srv.rst

@@ -6769,7 +6769,9 @@ The following standards are currently supported in Kea:
 
 -  *Server Identifier Override sub-option for the Relay Agent Option*, `RFC 5107
    <https://tools.ietf.org/html/rfc5107>`__: The server identifier override
-   sub-option is supported.
+   sub-option is supported. The implementation is not complete according to the
+   RFC, because the server does not store the RAI, but the functionality handles
+   expected use cases.
 
 Known RFC Violations
 --------------------

src/bin/dhcp4/dhcp4_srv.cc

@@ -3695,6 +3695,8 @@ Dhcpv4Srv::acceptServerId(const Pkt4Ptr& query) const {
         return (false);
     }
 
+    // According to RFC5107, the RAI_OPTION_SERVER_ID_OVERRIDE option if
+    // present, should match DHO_DHCP_SERVER_IDENTIFIER option.
     OptionPtr rai_option = query->getOption(DHO_DHCP_AGENT_OPTIONS);
     if (rai_option) {
         OptionPtr rai_suboption = rai_option->getOption(RAI_OPTION_SERVER_ID_OVERRIDE);