bin/94743: dhclient(8) should send hostname [patch]

[Frank Behrens]

>Number:         94743
>Category:       bin
>Synopsis:       dhclient(8) should send hostname [patch]
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          change-request
>Submitter-Id:   current-users
>Arrival-Date:   Mon Mar 20 17:30:16 GMT 2006
>Closed-Date:
>Last-Modified:
>Originator:     Frank Behrens
>Release:        FreeBSD 6.1-PRERELEASE-200602270917 i386
>Organization:
>Environment:
>Description:
dhclient(8) should send the clients hostname to DHCP server.
In that case the DHCP server can make dynamic updates on
a DNS server. This simplifies the setup of DHCP client networks.

With this change a default FreeBSD installation, where the network
adapter is configured by DHCP, is immediately visible in DNS
with forward and reverse lookups for the given host name. It is 
however required that DHCP and DNS server are setup accordingly.
The ability to overwrite the hostname with another value
in dhclient.conf(5) is not affected.

A short investigation shows the behaviour of default operating system
installations (tcpdump):

Knoppix 5.0 as Debain based Linux with pump(8) as DHCP client:
	  Client Ethernet Address: 00:0c:29:c6:cb:9b
	  Vendor-rfc1048:
	    DHCP:REQUEST
	    CID:[ether]00:0c:29:c6:cb:9b
	    MSZ:548
	    PR:SM+DG+NS+DN+BR+HN+LOG+LPR+NTP+XFS+XDM+MTU
	    HN:"Knoppix^@"
	    LT:43200
	    SID:192.168.99.10
	    RQ:192.168.99.70

Windows XP SP2 (Windows-98 not traced, but same behaviour):
	  Client Ethernet Address: 00:10:dc:31:73:47
	  Vendor-rfc1048:
	    DHCP:REQUEST
	    CID:[ether]00:10:dc:31:73:47
	    RQ:192.168.99.69
	    SID:192.168.99.10
	    HN:"myhost"
	    VC:"MSFT 5.0"
	    PR:SM+DN+DG+NS+WNS+WNT+WSC+RD+SR+T249+VO

NetBSD, FreeBSD 4.2, FreeBSD 6.x:	    
	  Client Ethernet Address: 00:0c:29:c6:cb:9b
	  Vendor-rfc1048:
	    DHCP:REQUEST
	    RQ:192.168.99.70
	    PR:SM+BR+TZ+DG+DN+NS+HN

FreeBSD 6.x with patch:	   
	  Client Ethernet Address: 00:0c:29:c6:cb:9b
	  Vendor-rfc1048:
	    DHCP:REQUEST
	    RQ:192.168.99.70
	    HN:"myhost"
	    PR:SM+BR+TZ+DG+DN+NS+HN

FreeBSD 6.x with patch and SEND_CLIENT_IDENTIFIER:	   
          Client Ethernet Address: 00:0c:29:c6:cb:9b
          Vendor-rfc1048:
            DHCP:REQUEST
            RQ:192.168.99.65
            CID:[ether]00:0c:29:c6:cb:9b
            HN:"myhost"
            PR:SM+BR+TZ+DG+DN+NS+HN


In the patch is a not activated section "SEND_CLIENT_IDENTIFIER". If
enabled dhclient sends a client identifier compatible with RFC2132,9.14.
This identifier is always sent from Windows clients and can be switched on
via command line argument on Linux pump(8). It may be activated to provide
better compatibility with Windows clients, but the author can not rate 
the advantages.

proposed MFC: after 6.1R
	
>How-To-Repeat:
>Fix:
Index: dhclient.c
===================================================================
RCS file: /data/freebsd/src/sbin/dhclient/dhclient.c,v
retrieving revision 1.6.2.4
diff -u -r1.6.2.4 dhclient.c
--- dhclient.c	24 Jan 2006 05:59:27 -0000	1.6.2.4
+++ dhclient.c	20 Mar 2006 16:38:24 -0000
@@ -54,6 +54,7 @@
  */
 
 #include <sys/cdefs.h>
+#include <unistd.h>
 __FBSDID("$FreeBSD: src/sbin/dhclient/dhclient.c,v 1.6.2.4 2006/01/24 05:59:27 brooks Exp $");
 
 #include "dhcpd.h"
@@ -1553,6 +1554,40 @@
 			    ip->client->config->send_options[i].len;
 			options[i]->timeout = 0xFFFFFFFF;
 		}
+		
+	/* send host name if not set via config file. */
+	char hostname[_POSIX_HOST_NAME_MAX+1];
+	if (!options[DHO_HOST_NAME]) {
+		if (gethostname(hostname, sizeof(hostname)) == 0) {
+			size_t len;
+			char* posDot = strchr(hostname, '.');
+			if (posDot != NULL)
+				len = posDot - hostname;
+			else
+				len = strlen(hostname);
+			options[DHO_HOST_NAME] = &option_elements[DHO_HOST_NAME];
+			options[DHO_HOST_NAME]->value = hostname;
+			options[DHO_HOST_NAME]->len = len;
+			options[DHO_HOST_NAME]->buf_size = len;
+			options[DHO_HOST_NAME]->timeout = 0xFFFFFFFF;
+		}
+	}
+
+#ifdef SEND_CLIENT_IDENTIFIER	
+	/* set unique client identifier */
+	char client_ident[sizeof(struct hardware)];
+	if (!options[DHO_DHCP_CLIENT_IDENTIFIER]) {
+		int hwlen = (ip->hw_address.hlen < sizeof(client_ident)-1) ?
+				ip->hw_address.hlen : sizeof(client_ident)-1;
+		client_ident[0] = ip->hw_address.htype;
+		memcpy(&client_ident[1], ip->hw_address.haddr, hwlen); 
+		options[DHO_DHCP_CLIENT_IDENTIFIER] = &option_elements[DHO_DHCP_CLIENT_IDENTIFIER];
+		options[DHO_DHCP_CLIENT_IDENTIFIER]->value = client_ident;
+		options[DHO_DHCP_CLIENT_IDENTIFIER]->len = hwlen+1;
+		options[DHO_DHCP_CLIENT_IDENTIFIER]->buf_size = hwlen+1;
+		options[DHO_DHCP_CLIENT_IDENTIFIER]->timeout = 0xFFFFFFFF;
+	}
+#endif	
 
 	/* Set up the option buffer... */
 	ip->client->packet_length = cons_options(NULL, &ip->client->packet, 0,


>Release-Note:
>Audit-Trail:
>Unformatted: