DHCP Client Debug Verbosity

Russell Dekema dekemar at umich.edu
Tue Nov 24 09:56:51 UTC 2015

On Tue, Nov 24, 2015 at 2:56 AM, Simon Hobson <dhcp1 at thehobsons.co.uk> wrote:
> sthaug at nethelp.no 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.

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