sd-dhcp-client: allways request broadcast

On systems which cannot receive unicast packets until its IP stack has been configured
we need to request broadcast packets. We are currently not able to reliably detect when
this is necessary, so set it unconditionally for now.

This is set on all packets, but the DHCP server will only broadcast the packets that are
necessary, and unicast the rest.

For more information please refer to this thread in CoreOS: https://github.com/coreos/bugs/issues/12

[tomegun: rephrased commit message]

diff --git a/src/libsystemd-network/sd-dhcp-client.c b/src/libsystemd-network/sd-dhcp-client.c
index 0300a6be93162d23eda68e378d94244a86518d5a..8f549060bf9750c8902544bddd8aa630663978ea 100644 (file)
--- a/src/libsystemd-network/sd-dhcp-client.c
+++ b/src/libsystemd-network/sd-dhcp-client.c
@@ -286,6 +286,15 @@ static int client_message_init(sd_dhcp_client *client, DHCPPacket **ret,
            refuse to issue an DHCP lease if 'secs' is set to zero */
         packet->dhcp.secs = htobe16(client->secs);
 
+        /* RFC2132 section 4.1
+           A client that cannot receive unicast IP datagrams until its protocol
+           software has been configured with an IP address SHOULD set the
+           BROADCAST bit in the 'flags' field to 1 in any DHCPDISCOVER or
+           DHCPREQUEST messages that client sends.  The BROADCAST bit will
+           provide a hint to the DHCP server and BOOTP relay agent to broadcast
+           any messages to the client on the client's subnet. */
+        packet->dhcp.flags = htobe16(0x8000);
+
         /* RFC2132 section 4.1.1:
            The client MUST include its hardware address in the ’chaddr’ field, if
            necessary for delivery of DHCP reply messages.