SUMMARY:How do I choice a hostid ?

From: Edmond Sully (
Date: Fri Nov 27 1998 - 20:05:01 CST

Thanks for all the replies.

Original Message:

>I'm replacing a NVRAM of invalid content by a new one. So, I want to
>configure the hostid.I read the document which explains how to
>programming a hostid but, It is not clear on the way to choice it. I
>know that the first three bytes are 08:0:20. My question is:
>How to decide the others bytes? I have a SS2/sun4c/60.

Good answer from:

1)"Marco Greene" <>
<Actually, the 08:00:20 are the first three hex numbers for your
address. It is VERY important that you do not duplicate one that is
already being used on that LAN. Maybe try using something like
Your ethernet address (MAC address) is used by the ARP protocol.

Now for your hostid that is a number used by most licensed programs. If
have licensed programs (that use the hostid, it is imparative that you
the same number for you hostid.>

2)"Paramasivam, Meenakshisundaram" <>
<Why don't you keep the same hostid of previous NVRAM?>

3)TSI Europe Helpdesk <>

<You will find the the NVRAM/hostid FAQ very helpful. It is available

4)Vincent Campbell <>

<The three bytes 08:0:20 are in fact the first three bytes of the
address. The hostid is located in bytes 1, c(12), d(13) and e(14) of the
IDPROM part of NVRAM. I see you have the hostid FAQ, but the following
a summary of what you need to do ... some taken from the FAQ.

Note that for you (SS2) the first byte of the hostid should be 55.

First, record your original hostid, just in case you want
to change it back. If you can do this, it is also a good idea to
get a copy of important PROM information and store it somewhere.
        * SunOs : /usr/etc/devinfo -vp
        * Solaris : /usr/sbin/prtconf -vp
The hostid is stored in the IDPROM part of NVRAM. The IDPROM
takes up the first 16 bytes and the meaning of these bytes is
as follows:
 byte(s) contents
 ------- --------
 0 always 01 - format/version number
 1 first byte of hostid (machine type) (SS2 = 55)
 2-7 6 byte ethernet address (first three bytes should be
 8-b date of manufacture (usually all 0s, doesn't really matter)
 c second byte of hostid
 d third byte of hostid
 e fourth byte of hostid
 f IDPROM checksum - bitwise xor of bytes 0-e
You must first go to the OpenBoot monitor:
>From the OpenBoot monitor "ok" prompt you can view the IDPROM
data by typing .idprom
To change a byte use : <new value> < byte nr> mkp
For example, to change the hostid to 55a1b3c3 you need to:
        ok 1 55 mkp
        ok c a1 mkp
        ok d b3 mkp
        ok e c5 mkp

Now the hostid is changed but the checksum is wrong. This is
and written to location f with the command:
        ok 0 f 0 do i idprom@ xor loop f mkp
You can view a particular byte by typing <byte nr> idprom .
E.g. : To view checksum:
ok f idprom@ . (dot is important!)>

Edmond Sully, REHRED Sys. Admin.
Port-Au-Prince, Haiti

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