====== Booting from an iSCSI target ======

===== Configuring your DHCP Server =====

==== Using ISC dhcpd ====

Place the following two lines in ///etc/dhcpd.conf//:

    filename "";
    option root-path "iscsi:my.target.dns.name::::iqn.2007-08.name.dns.target.my:iscsiboot";

where //my.target.dns.name// is the DNS name (or IP address) of your iSCSI target, and //iqn.2007-08.name.dns.target.my:iscsiboot// is the iSCSI target IQN that you wish to boot from.

You will probably need to restart your DHCP server for the changes to take effect:

    /etc/init.d/dhcpd restart

==== Using Microsoft DHCP Server ====

In the DHCP administrative tool, right-click on //Server Options// and choose //Configure Options//.  Click on "017 Root Path" and set the "String value" to

    iscsi:my.target.dns.name::::iqn.2007-08.name.dns.target.my:iscsiboot

where //my.target.dns.name// is the DNS name (or IP address) of your iSCSI target, and //iqn.2007-08.name.dns.target.my:iscsiboot// is the iSCSI target IQN that you wish to boot from.

{{ :screenshots:winnt_dhcp_iscsi.png?716×511 |Windows DHCP server configuration}}

===== Booting Your Client =====

Boot your diskless client using gPXE.  If all has gone well, you should see it boot from your iSCSI target image.

{{:sanboot:sanbootcli.jpg}}

Congratulations on a successful boot from SAN!

\\
\\

===== Troubleshooting =====

If you have difficulties booting Windows from SAN, take a look at [[:sanboot:winnt_iscsi_debug|Debugging Windows iSCSI boot]].

===== iSCSI Root Path Syntax =====

==== Theory ====

Described heavily in depth in RFC 4173, the root path string used to boot from SAN can range from relatively simple, to a //very// explicit, information packed line.  According to the RFC, the root path string is formatted as follows:

  iscsi:<servername>:[protocol]:[port]:[LUN]:<targetname>

**"servername"** is required, and can be the domain name or IPv4 (or IPv6, which is //not// supported by gPXE) address of your iSCSI target server.\\ 
**"protocol"** is optional, and is generally left blank, assuming a default value of "6" for TCP.\\ 
    * RFC 4173 states that TCP is the only valid protocol at the time of writing.\\ 
**"port"** is optional, and if left blank will assume a default value of 3260.\\ 
**"LUN"** is optional, and if left blank will assume a default value of 0.\\ 
**"targetname"** is required, and should be the iSCSI target IQN you wish to boot from.\\ 

==== Practice ====

For most non-complex deployments, such as the samples in above sections, your root path will look like:

  iscsi:my.target.dns.name::::iqn.2007-08.name.dns.target.my:iscsiboot

That root path string omits the protocol, port, and LUN used by the iSCSI target server, defaulting to TCP, port 3260, and LUN 0, but is functionally equivalent to:

  iscsi:my.target.dns.name:6:3260:0:iqn.2007-08.name.dns.target.my:iscsiboot

Furthermore, the LUN ID itself has a rather sophisticated set of rules for how it can be defined, but that goes beyond the scope of this article.

==== Advanced Reading ====

For more information, please see pages 3 and 4 of [[http://www.rfc-archive.org/getrfc.php?rfc=4173|RFC 4173]].