diff --git a/doc/sphinx/arm/hooks-bootp.rst b/doc/sphinx/arm/hooks-bootp.rst
index b687d6c003..8e55f7d6dc 100644
--- a/doc/sphinx/arm/hooks-bootp.rst
+++ b/doc/sphinx/arm/hooks-bootp.rst
@@ -15,6 +15,10 @@ a dhcp-message-type option and put into the "BOOTP" client class.
 Members of this class get infinite lifetime leases but the class can
 be used too for instance to guard a pool of addresses.
 
+On output dhcp-message-type and other DHCP specific options are removed
+and responses shorter than the BOOTP minimum size (300 octets) are
+padded to this size.
+
 The library is available since Kea 1.7.2 and can be loaded in a
 similar way as other hook libraries by the ``kea-dhcp4`` process.
 It takes no parameter.
diff --git a/src/hooks/dhcp/bootp/bootp.dox b/src/hooks/dhcp/bootp/bootp.dox
index c110036bf1..68489b027c 100644
--- a/src/hooks/dhcp/bootp/bootp.dox
+++ b/src/hooks/dhcp/bootp/bootp.dox
@@ -1,4 +1,4 @@
-// Copyright (C) 2019-2010 Internet Systems Consortium, Inc. ("ISC")
+// Copyright (C) 2019-2020 Internet Systems Consortium, Inc. ("ISC")
 //
 // This Source Code Form is subject to the terms of the Mozilla Public
 // License, v. 2.0. If a copy of the MPL was not distributed with this
@@ -53,11 +53,16 @@ bootp_callouts.cc. It checks if the necessary parameter is passed and
 decodes the option configurations. @ref unload() free the configuration.
 
 Kea engine checks if the library has functions that match known hook
-point names. This library has one such function: @ref buffer4_receive
-located in bootp_callouts.cc.
+point names. This library has two such functions: @ref buffer4_receive
+and @ref pkt4_send located in bootp_callouts.cc.
 
-If the receive query has to dhcp-message-type option then it is a BOOTP
+If the receive query has no dhcp-message-type option then it is a BOOTP
 one: the BOOTP client class and a DHCPREQUEST dhcp-message-type option
 are added to the BOOTP query.
 
+On the outgoing side dhcp-message-type and other DHCP specific options
+are removed from the response. When the packed response is shorter than
+the BOOTP minimum size (300 octets) it is padded after the END option
+by nuls up to this size.
+
 */