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Today's Topics:
1. Dealing with possible list of numeric option values
(pxe-system-type) (Boylan, Ross)
2. Re: Dealing with possible list of numeric option values
(pxe-system-type) (glenn.satch...@uniq.com.au)
----------------------------------------------------------------------
Message: 1
Date: Mon, 16 Nov 2020 04:22:25 +0000
From: "Boylan, Ross" <ross.boy...@ucsf.edu>
To: "dhcp-users@lists.isc.org" <dhcp-users@lists.isc.org>
Cc: Ross Boylan <rossboy...@stanfordalumni.org>
Subject: Dealing with possible list of numeric option values
(pxe-system-type)
Message-ID:
<byapr05mb573688f97e4d8eda8b53deee87...@byapr05mb5736.namprd05.prod.outlook.com>
Content-Type: text/plain; charset="iso-8859-1"
According to RFC 4578 and the dhcp-options man page, pxe-system-type has values
that are a list of one or more uint16's. dhcp-eval and dhcp-options didn't seem
to say exactly how I could work with it, or, more directly, what the result of
using "option pxe-system-type" in a conditional expression is: a string? a
number? a list?
My first guess was
if option pxe-system-type = 7 then ....
Should that work? I notice all the examples on this list seem to use the form
if option pxe-system-type = 00:07 then ..
suggesting the values are converted to a stream of bytes after promotion to 32
bit integer size.
Further, it sounds as if there might be multiple values supplied. Is there any
good way to figure if 7 is one of them?
Will option pxe-system-type = 00:07 fail if there is more than one element
returned, even if the first one is 7?
Maybe in practice it is never an issue?
I'm also curious how options that are lists with elements other than numbers
work.
Thanks.
Ross Boylan
cc's appreciated
------------------------------
Message: 2
Date: Mon, 16 Nov 2020 17:36:19 +1100
From: glenn.satch...@uniq.com.au
To: Users of ISC DHCP <dhcp-users@lists.isc.org>
Subject: Re: Dealing with possible list of numeric option values
(pxe-system-type)
Message-ID: <5debfd2d46c8da9eccef842a6d927...@uniq.com.au>
Content-Type: text/plain; charset=US-ASCII; format=flowed
Hi Ross
Lists are encoded as a byte stream of concatenated values, so a list of
int32 would be groups of 4 bytes, int16 as groups of 2 bytes, etc.
You might be able to use the regex match to pick a value in the
subsequent byte stream, regex is defined in dhcp-eval as
data-expression-1 ~= data-expression-2
such as
if option pxe-system-type ~= 00:07 then ...
I haven't tested this, so you may want to verify my suggestion.
regards,
Glenn
On 2020-11-16 15:22, Boylan, Ross wrote:
> According to RFC 4578 and the dhcp-options man page, pxe-system-type
> has values that are a list of one or more uint16's. dhcp-eval and
> dhcp-options didn't seem to say exactly how I could work with it, or,
> more directly, what the result of using "option pxe-system-type" in a
> conditional expression is: a string? a number? a list?
>
> My first guess was
> if option pxe-system-type = 7 then ....
> Should that work? I notice all the examples on this list seem to use
> the form
> if option pxe-system-type = 00:07 then ..
> suggesting the values are converted to a stream of bytes after
> promotion to 32 bit integer size.
>
> Further, it sounds as if there might be multiple values supplied. Is
> there any good way to figure if 7 is one of them?
> Will option pxe-system-type = 00:07 fail if there is more than one
> element returned, even if the first one is 7?
> Maybe in practice it is never an issue?
>
> I'm also curious how options that are lists with elements other than
> numbers work.
>
> Thanks.
> Ross Boylan
> cc's appreciated
> _______________________________________________
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