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Hi,
I've configured my RedHat 7.1 linux system with a
customised 2.4.9 kernel, Intel EtherPro100 network card and a Terayon Terajet
cablemodem.
When I try to obtain an IP address from my ISP (NTL
in the UK) using dhclient v3.0rc12 I see DHCPDISCOVER messages going out but no
DHCPOFFERs, DCHPRESPONSEs, or DHCPACKs are being returned. I know the
connection is working as my Win2k system works fine. So, I decided to monitor
the network to see what Win2k was sending and try reproduce that on my linux
system to see if I could get it to work.
This is what my Win2k system
sends:
Frame Time Src MAC
Addr Dst MAC Addr Protocol
Description Src Other Addr
Dst Other Addr Type Other Addr
2 2.234375
LOCAL *BROADCAST
DHCP
Discover
(xid=5AD055E0)
0.0.0.0 255.255.255.255
+ Frame: Base frame properties + ETHERNET: ETYPE = 0x0800 : Protocol = IP: DOD Internet Protocol + IP: ID = 0xC6E; Proto = UDP; Len: 328 + UDP: IP Multicast: Src Port: BOOTP Client, (68); Dst Port: BOOTP Server (67); Length = 308 (0x134) DHCP: Discover (xid=5AD055E0) DHCP: Op Code (op) = 1 (0x1) DHCP: Hardware Type (htype) = 1 (0x1) 10Mb Ethernet DHCP: Hardware Address Length (hlen) = 6 (0x6) DHCP: Hops (hops) = 0 (0x0) DHCP: Transaction ID (xid) = 1523602912 (0x5AD055E0) DHCP: Seconds (secs) = 0 (0x0) DHCP: Flags (flags) = 0 (0x0) DHCP: 1............... = Broadcast DHCP: Client IP Address (ciaddr) = 0.0.0.0 DHCP: Your IP Address (yiaddr) = 0.0.0.0 DHCP: Server IP Address (siaddr) = 0.0.0.0 DHCP: Relay IP Address (giaddr) = 0.0.0.0 DHCP: Client Ethernet Address (chaddr) = <my NT MAC address> DHCP: Server Host Name (sname) = <Blank> DHCP: Boot File Name (file) = <Blank> DHCP: Magic Cookie = 99.130.83.99 DHCP: Option Field (options) DHCP: DHCP Message Type = DHCP Discover DHCP: AutoConfigure = YES DHCP: Client-identifier = (Type: 1) <my NT MAC address> DHCP: Requested Address = <a previously registered IP address> DHCP: Host Name = <NT hostname> DHCP: Client Class information = (Length: 8) 4d 53 46 54 20 35 2e 30 DHCP: Parameter Request List = (Length: 10) 01 0f 03 06 2c 2e 2f 1f 21 2b DHCP: End of this option field This is how I've configured
my dhclient.conf file to try and reproduce the above:
option autoconfigure code 251 =
boolean;
interface "eth0"
{
send autoconfigure on; send dhcp-client-identifier 01:<my registered MAC address>; send
host-name "<Linux
hostname>";
send vendor-class-identifier "MSFT 5.0"; request subnet-mask, domain-name, routers, domain-name-servers, netbios-name-servers, netbios-node-type, netbios-scope, router-discovery, static-routes, vendor-encapsulated-options; prepend domain-name-servers 194.168.4.100, 194.168.8.100; media "media 10baseT/UTP"; } And now, this is what my Linux system sends using
dhclient v3.0rc12 and the above config file:
Frame Time Src MAC
Addr Dst MAC Addr Protocol
Description Src Other Addr Dst Other
Addr Type Other Addr
7 5.805000
INTEL nanana *BROADCAST
DHCP
Discover
(xid=0784194B) 0.0.0.0
255.255.255.255
+ Frame: Base frame properties + ETHERNET: ETYPE = 0x0800 : Protocol = IP: DOD Internet Protocol + IP: ID = 0x0; Proto = UDP; Len: 328 + UDP: IP Multicast: Src Port: BOOTP Client, (68); Dst Port: BOOTP Server (67); Length = 308 (0x134) DHCP: Discover (xid=0784194B) DHCP: Op Code (op) = 1 (0x1) DHCP: Hardware Type (htype) = 1 (0x1) 10Mb Ethernet DHCP: Hardware Address Length (hlen) = 6 (0x6) DHCP: Hops (hops) = 0 (0x0) DHCP: Transaction ID (xid) = 126097739 (0x784194B) DHCP: Seconds (secs) = 0 (0x0) DHCP: Flags (flags) = 0 (0x0) DHCP: 0............... = No Broadcast DHCP: Client IP Address (ciaddr) = 0.0.0.0 DHCP: Your IP Address (yiaddr) = 0.0.0.0 DHCP: Server IP Address (siaddr) = 0.0.0.0 DHCP: Relay IP Address (giaddr) = 0.0.0.0 DHCP: Client Ethernet Address (chaddr) = <my Linux MAC address> DHCP: Server Host Name (sname) = <Blank> DHCP: Boot File Name (file) = <Blank> DHCP: Magic Cookie = 99.130.83.99 DHCP: Option Field (options) DHCP: DHCP Message Type = DHCP Discover DHCP: Host Name = <Linux hostname> DHCP: AutoConfigure = YES DHCP: Parameter Request List = (Length: 10) 01 0f 03 06 2c 2e 2f 1f 21 2b DHCP: Client Class information = (Length: 8) 4d 53 46 54 20 35 2e 30 DHCP: Client-identifier = (Type: 1) <my registered MAC address> DHCP: End of this option field With the output from running dhclient below:
[root@<Linux hostname> /root]# dhclient -1
Internet Software Consortium DHCP Client V3.0rc12 Copyright 1995-2001 Internet Software Consortium. All rights reserved. For info, please visit http://www.isc.org/products/DHCP Listening on LPF/eth0/<my Linux MAC address>
Sending on LPF/eth0/<my Linux MAC address> Sending on Socket/fallback Trying medium "media 10baseT/UTP" 1 DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 5 Trying medium "media 10baseT/UTP" 1 DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 7 Trying medium "media 10baseT/UTP" 1 DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 8 Trying medium "media 10baseT/UTP" 1 DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 11 Trying medium "media 10baseT/UTP" 1 DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 14 Trying medium "media 10baseT/UTP" 1 DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 16 No DHCPOFFERS received. Unable to obtain a lease on first try. Exiting. [root@<Linux hostname> /root]# As you can see the DHCPDISCOVER packets are pretty simular, apart
from the Broadcast flag and Request IP address option being set on my NT system.
Reading the RFC2131 (DHCP) it suggests that the Broadcast flag should be
set if a computer systems IP stack cannot handle being passed a
unicast packet before an IP address has been registered. Here's an extract
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. A client that can receive
unicast IP datagrams before its protocol software has been configured
SHOULD
clear the BROADCAST bit to 0. The BOOTP clarifications
document discusses the ramifications of the use of the BROADCAST bit [21].
Consequently, I believe if I set the Broadcast flag on my linux system I
will recieve a DHCPOFFER and things will burst into life (wishful
thinking)!!!
Therefore, I need to know whether this behaviour is
a bug/feature of dhclient 3.0rc12 or for someone to explain to me how I go about
setting the broadcast flag on my linux system to true (hacking the source code
of dhclient 3.0rc12 is NOT an option). Please can anyone assist me.
Thanks,
Andrew
Leach |
Help requested - dhclient 3.0rc12 and a cablemodem
Andrew Leach via ntlworld.com Thu, 20 Sep 2001 14:16:58 -0700
