- /* Some DHCP servers will send bigger DHCP packets than the
- defined default size unless the Maximum Messge Size option
- is explicitely set */
- max_size = htobe16(DHCP_IP_UDP_SIZE + DHCP_MESSAGE_SIZE +
- DHCP_MIN_OPTIONS_SIZE);
- r = dhcp_option_append(opt, optlen,
- DHCP_OPTION_MAXIMUM_MESSAGE_SIZE,
- 2, &max_size);
- if (r < 0)
- return r;
- }
+ /* RFC2131 section 3.5:
+ The client SHOULD include the ’maximum DHCP message size’ option to
+ let the server know how large the server may make its DHCP messages.
+
+ Note (from ConnMan): Some DHCP servers will send bigger DHCP packets
+ than the defined default size unless the Maximum Messge Size option
+ is explicitely set
+
+ RFC3442 "Requirements to Avoid Sizing Constraints":
+ Because a full routing table can be quite large, the standard 576
+ octet maximum size for a DHCP message may be too short to contain
+ some legitimate Classless Static Route options. Because of this,
+ clients implementing the Classless Static Route option SHOULD send a
+ Maximum DHCP Message Size [4] option if the DHCP client's TCP/IP
+ stack is capable of receiving larger IP datagrams. In this case, the
+ client SHOULD set the value of this option to at least the MTU of the
+ interface that the client is configuring. The client MAY set the
+ value of this option higher, up to the size of the largest UDP packet
+ it is prepared to accept. (Note that the value specified in the
+ Maximum DHCP Message Size option is the total maximum packet size,
+ including IP and UDP headers.)
+ */
+ max_size = htobe16(size);
+ r = dhcp_option_append(&packet->dhcp, client->mtu, &optoffset, 0,
+ DHCP_OPTION_MAXIMUM_MESSAGE_SIZE,
+ 2, &max_size);
+ if (r < 0)
+ return r;
+
+ *_optlen = optlen;
+ *_optoffset = optoffset;
+ *ret = packet;
+ packet = NULL;