{"id":4177,"date":"2012-07-25T09:24:42","date_gmt":"2012-07-25T07:24:42","guid":{"rendered":"https:\/\/ingmarverheij.com\/?p=4177"},"modified":"2012-07-25T09:37:55","modified_gmt":"2012-07-25T07:37:55","slug":"configure-hostname-via-dhcp","status":"publish","type":"post","link":"https:\/\/ingmarverheij.com\/en\/configure-hostname-via-dhcp\/","title":{"rendered":"Configure hostname via DHCP"},"content":{"rendered":"

\"Windows<\/a>A system can be identified on a network with a MAC address<\/a>, IP address<\/a> or its hostname<\/a>. The hostname is the most readable form for humans, especially because you have the ability to change the hostname (unlike a MAC address and only partially for an IP address).<\/p>\n

Giving the device a human readable hostname makes it easier to troubleshoot issues and is sometimes required to to apply to a naming convention. Having an asset tag on the device makes it easier for a user to explain what device he\/she is using.<\/p>\n

But what if you\u2019re unable to change the hostname of a device or don\u2019t want to specify this for each device? Think of thin clients (or zero clients) like a HP Smart Zero Client<\/a> where you can\u2019t (or want) to configure the hostname per device. <\/p>\n

Well, you can push the hostname via the Dynamic Host Configuration Protocol (DHCP)<\/a>.<\/p>\n

<\/p>\n

DHCP<\/h2>\n

A client can be configured with static or dynamic IP configuration, by default all systems are configured with a dynamic configuration. This means that a client requests an IP configuration from a server on the network, the DHCP server. DHCP works basically works in three phases:<\/p>\n

    \n
  1. Initialization <\/li>\n
  2. Renewing <\/li>\n
  3. Rebinding <\/li>\n<\/ol>\n

    \"\"<\/a>During the startup process of a system (or actually the network stack) there is no IP configuration and therefore it needs to initialize. During this phase (at least) 4 packets are broadcasted,<\/p>\n

    After receiving (and confirming) an IP configuration, a DHCP lease, a timer monitors when the half of the lease time T1 (typical lease time is 8 hours, so T1 is 4 hours) is expired. A unicast is sent to the DHCP server to renew the configuration. If the renewing phase fails (for what ever reason) the same request is sent as a broadcast the Rebinding phase). After the lease expires the whole process starts from the Initialization phase.<\/p>\n

    <\/strong><\/p>\n

    DHCP options<\/strong><\/p>\n

    Besides offering an IP address the DHCPOFFER packet contains a list op DHCP options. The most common used are:<\/p>\n

         001 \u2013 Subnet Mask<\/p>\n

         003 \u2013 Router<\/p>\n

         006 \u2013 Domain Name Server<\/p>\n

         015 \u2013 Domain Name<\/p>\n

    With BOOTP \/ DHCP option 012<\/a> a host name can be supplied, but only if the client requests a hostname.<\/p>\n

     <\/p>\n

    <\/h2>\n

    Server configuration<\/h2>\n

    On the DHCP server you need to specify what name (hostname) you need to give to what device (MAC address), this is done with a reservation. You need to create a reserveration for each <\/em>device and therefore you need to know the MAC address of all of those device.<\/p>\n

     <\/h4>\n

    Linux<\/h4>\n

    If your using a linux server as your DHCP server you\u2019re probable using dhcpd<\/em><\/a> (DHCP daemon)<\/em>. You can add a reservation with the following lines in dhcpd.conf<\/a>.<\/strong><\/p>\n

    host LAPTOP_IV { \n   hardware ethernet 60:6B:BD:0B:67:3F; \n   fixed-address 192.168.0.101;\n   option host-name "LAPTOP_IV";\n}\n\nhost THN-WG-2012 { \n   hardware ethernet 9C:8E:99:E7:1A:B8; \n   fixed-address 192.168.0.102;\n   option host-name "THN-WG-2012";\n}<\/pre>\n
    <\/strong><\/p>\n
    <\/strong><\/p>\n
     <\/h4>\n
    Windows<\/h4>\n
    The following procedure explains how to add a reservation for a device and specify a hostname in a Windows 2008 R2 Server.<\/p>\n
      \n
    1. In the left pane, select the Address Leases <\/strong>in the scope where the device has a DHCP lease<\/li>\n
    2. Right-click the DHCP lease<\/strong>, and then select Add to Reservation
      \n      
      \"\"<\/a><\/strong><\/li>\n
    3. In the left pane, select the Reservations<\/strong> in the scope where the device has a DHCP lease\"\"<\/a><\/li>\n
    4. Right-click the Reservations<\/strong>, and then click Configure Options
      \n      
      \"\"<\/a><\/strong><\/li>\n
    5. Select option 012 Host Name<\/strong> and enter the name of the device in the Data entry<\/strong> field\n
          
      \"\"<\/a><\/li>\n
    6. Verify the information is correct and click OK
      \n      
      \"\"<\/a><\/strong><\/li>\n<\/ol>\n
      \n  
      <\/p>\n
      Client configuration<\/h2>\n
      Linux <\/h4>\n
      \"\"<\/a>On a a device with a Linux operating system the dhclient<\/a>  provides a means for configuring network interfaces using DHCP (or BOOTP). The configuration is \"\"<\/a>stored in the dhclient.conf file (which can be found in \/etc\/dhcp<\/strong>). <\/p>\n
      In this configuration file you can specify which DHCP options the client should request (and honor) with the DHCPREQUEST packet. One of the options you can specify is:<\/p>\n
      request host-name<\/pre>\n
       <\/h4>\n
      Windows <\/h4>\n
      Unfortunately Microsoft has not implemented DHCP option 012 (Host Name) in the DHCP client.<\/p>\n