Saturday, October 14, 2006

Booting Thin Client Diskless Workstation

Bootp, shorts for Bootstrap Protocol, is an UDP network protocol which is originally defined in RFC 951 to assign IP address for network clients. Bootp is well suitable to apply in diskless workstation, workstation without operating system installed, or simply called thin client.

Bootp is not DHCP! Although both of these two protocols sound similar at first thought, but they are technically different and could be co-exists in the same server or network segment.

Hospitality management system giant, Micros System Inc, makes good use of bootp in its high rank Point-Of-Sale system called Micros 8700 HMS.

When the diskless Micros PC Workstation power on, the bootp enabled network interface card will broadcast its MAC address to the network. When the bootp daemon running on the Micros host receives the broadcast packets, it will assign a valid IP address follow by transferring a DOS operating system image to the PC Workstation according to the MAC-IP-Image mapping maintained in the bootpd configuration file.

Once the image transferring (via tftp protocol) completed, the diskless PC Workstation starts to boot up with the OS image parking in memory segment that act as RAM-DISK. When the boot up completed, the Micros diskless PC workstation functions as if it is a normal desktop PC pre-installed with DOS OS.
Bootpd server and clients could be reside on different network segment by deploying bootp relay agent. To make thing simple or get it up and running right during initial roll out, put both bootpd server and client on the same network segment.

Checklist when thin client unable getting IP address:

  1. Replace a known good unit of thin client to rule out possibilities of

    • Faulty boot ROM embedded in NIC that is bootp enabled
    • Faulty Ethernet patch cable
    • faulty network access point or LAN point

  2. Bootp daemon is not running. In Linux/Unix, execute

    ps -ef | grep bootpd
    lsof -i | grep 67

    to confirm bootp daemon is running and listening to legacy port number (as shown in /etc/services file)

  3. Incorrect MAC address to IP address mapping maintained in /etc/bootptab bootpd configuration file

  4. ARP cache conflict at bootpd server. Executing the command

    arp -a

    to list the bootpd server arp cache. Confirm that there is no ARP cache conflict. To delete the conflict, for example conflict on IP address, execute command

    arp -d

  5. Use cross-over patch cable or straight Ethernet cable and a hub to directly link up the bootpd server and client to form an simple isolate network. If it works in this simple network infrastructure, then get network experts sit in for assistant. There might be firewalls or routers that have blocked the UDP packets from reaching to bootpd server.
Related information:
  • Tftp protocol in brief

    • Host A sends an read request (RRQ) or write request (WRQ) packet to host B. The packet containing the filename and transfer mode.
    • Host B replies with an acknowledgement packet (ACK) to WRQ or directly with a DATA packet in case of RRQ. The reply also serves to inform host A of which port on host B the remaining packets should be sent to.
    • The source host sends numbered DATA packets to the destination host, all but the last containing a full-sized block of data. The destination host replies with numbered ACK packets for all DATA packets.
    • The final DATA packet must contain less than a full-sized block of data to signal that it is the last. If the size of the transferred file is an exact multiple of the block-size, the source sends a final DATA packet containing 0 bytes of data.

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