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Today's Topics:
1. DHCP Client Debug Verbosity (Russell Dekema)
2. Re: DHCP Client Debug Verbosity ([email protected])
3. Re: DHCP Client Debug Verbosity (Simon Hobson)
4. Re: DHCP Client Debug Verbosity (Russell Dekema)
5. Re: DHCP Client Debug Verbosity (Russell Dekema)
----------------------------------------------------------------------
Message: 1
Date: Mon, 23 Nov 2015 19:27:45 -0500
From: Russell Dekema <[email protected]>
To: [email protected]
Subject: DHCP Client Debug Verbosity
Message-ID:
<CADoGSYgD3W5QWHiQSOkxXseiFyaPKKcE=9h+wa25_m6110f...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Good evening,
Beyond issuing the -v flag on the dhclient command line, is there a
way to increase the level or verbosity of debugging output?
I am trying to troubleshoot a problem in which the ISC DHCP client
sends a DHCPDISCOVER and I can see what seems like a valid DHCPOFFER
come back to the client over the wire, but the DHCP client appears to
be ignoring the offer. Adding the -v flag to the dhclient command line
does not produce any useful troubleshooting information; it simply
shows repeated DHCPDISCOVER frames being sent, and nothing else.
I have read the dhclient man page and searched the web extensively but
haven't found any way to do this. I am hoping for a middle ground
between "-v" and running the client in gdb or extensively
instrumenting the code with printf()s (or the like), as those are both
a bit outside my normal realm of expertise.
Thanks in advance for any suggestions.
Sincerely,
Rusty Dekema
------------------------------
Message: 2
Date: Tue, 24 Nov 2015 08:06:48 +0100 (CET)
From: [email protected]
To: [email protected], [email protected]
Subject: Re: DHCP Client Debug Verbosity
Message-ID: <[email protected]>
Content-Type: Text/Plain; charset=us-ascii
> I have read the dhclient man page and searched the web extensively but
> haven't found any way to do this. I am hoping for a middle ground
> between "-v" and running the client in gdb or extensively
> instrumenting the code with printf()s (or the like), as those are both
> a bit outside my normal realm of expertise.
Using tcpdump or Wireshark to look at the actual traffic can sometimes
be invaluable.
Steinar Haug, Nethelp consulting, [email protected]
------------------------------
Message: 3
Date: Tue, 24 Nov 2015 07:56:35 +0000
From: Simon Hobson <[email protected]>
To: Users of ISC DHCP <[email protected]>
Subject: Re: DHCP Client Debug Verbosity
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
[email protected] wrote:
>> I have read the dhclient man page and searched the web extensively but
>> haven't found any way to do this. I am hoping for a middle ground
>> between "-v" and running the client in gdb or extensively
>> instrumenting the code with printf()s (or the like), as those are both
>> a bit outside my normal realm of expertise.
>
> Using tcpdump or Wireshark to look at the actual traffic can sometimes
> be invaluable.
However, for most traffic, it can show you packets arriving on the wire which
are then dropped by a firewall (iptables rules) before reaching the application
to which they are addressed. I'm not sure if this applies to the dhcp client
since IIRC that uses raw sockets and bypasses the IP stack.
Yes, I've been had by this one often enough.
------------------------------
Message: 4
Date: Tue, 24 Nov 2015 04:56:51 -0500
From: Russell Dekema <[email protected]>
To: Users of ISC DHCP <[email protected]>
Subject: Re: DHCP Client Debug Verbosity
Message-ID:
<CADoGSYhLd7GnEyupr-ppidCK60=a9rphqk67avutqblebvs...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
On Tue, Nov 24, 2015 at 2:56 AM, Simon Hobson <[email protected]> wrote:
> [email protected] wrote:
>
>>> I have read the dhclient man page and searched the web extensively but
>>> haven't found any way to do this. I am hoping for a middle ground
>>> between "-v" and running the client in gdb or extensively
>>> instrumenting the code with printf()s (or the like), as those are both
>>> a bit outside my normal realm of expertise.
>>
>> Using tcpdump or Wireshark to look at the actual traffic can sometimes
>> be invaluable.
>
> However, for most traffic, it can show you packets arriving on the wire which
> are then dropped by a firewall (iptables rules) before reaching the
> application to which they are addressed. I'm not sure if this applies to the
> dhcp client since IIRC that uses raw sockets and bypasses the IP stack.
>
> Yes, I've been had by this one often enough.
This (offers getting dropped by iptables rules) definitely applies to
the DHCP client - at least when using DHCPv6. I learned that the hard
way last week on an unrelated case, and I don't see why it would be
any different with v4.
------------------------------
Message: 5
Date: Tue, 24 Nov 2015 06:26:15 -0500
From: Russell Dekema <[email protected]>
To: Users of ISC DHCP <[email protected]>
Subject: Re: DHCP Client Debug Verbosity
Message-ID:
<CADoGSYh5HnONu8fxT5eaNRds4yp5zHOfWY8wgG=ynj129mp...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
On Mon, Nov 23, 2015 at 7:27 PM, Russell Dekema <[email protected]> wrote:
> Good evening,
>
> Beyond issuing the -v flag on the dhclient command line, is there a
> way to increase the level or verbosity of debugging output?
>
> I am trying to troubleshoot a problem in which the ISC DHCP client
> sends a DHCPDISCOVER and I can see what seems like a valid DHCPOFFER
> come back to the client over the wire, but the DHCP client appears to
> be ignoring the offer. Adding the -v flag to the dhclient command line
> does not produce any useful troubleshooting information; it simply
> shows repeated DHCPDISCOVER frames being sent, and nothing else.
>
> I have read the dhclient man page and searched the web extensively but
> haven't found any way to do this. I am hoping for a middle ground
> between "-v" and running the client in gdb or extensively
> instrumenting the code with printf()s (or the like), as those are both
> a bit outside my normal realm of expertise.
>
> Thanks in advance for any suggestions.
>
> Sincerely,
> Rusty Dekema
To answer my own question and perhaps save a future troubleshooter
some time, the answer is to edit includes/site.h and uncomment as many
of the #define DEBUG_[xyz] lines as you see fit.
In my case, it revealed the following:
DHCPDISCOVER on ib0 to 255.255.255.255 port 67 interval 4 (xid=0x31fd9d0e)
DHCPOFFER in wrong transaction.
Off the top of your heads, does anyone know what goes into the
transaction matching logic other than the xid? According to my packet
captures, the xid on the received DHCPOFFER matches the xid on the
transmitted DHCPDISCOVER.
Cheers,
Rusty
------------------------------
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End of dhcp-users Digest, Vol 85, Issue 24
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