Re: dhcpdump not seeing dhclient messages
On Mon, 2013-08-26 at 06:46 -0400, Sean Alexandre wrote:
> On Mon, Aug 26, 2013 at 02:54:27PM +0530, Arun Khan wrote:
> > On Mon, Aug 26, 2013 at 2:01 PM, Sean Alexandre <sean@alexan.org> wrote:
> > > I have a machine that's not acquiring a DHCP lease from my ISP. I can see that
> > > dhclient is sending DHCPDISCOVER messages. My system log has:
> > >
> > > Aug 25 17:36:41 athabasca dhclient: DHCPDISCOVER on eth-wan to 255.255.255.255 port 67 interval 7
> >
> > -------------8<-------------8<-------------8<-------------8<-------------8<-------------8<-------------8<-------------
> >
> > > The odd thing is if I do the exact same thing with this machine connected to
> > > a local TP-LINK router instead of my ISP cable modem, dhcpdump sees the
> > > DHCPDISCOVER, and the machine acquires a DHCP lease.
> >
> OK, thanks. I just tried that now, and it got a DHCP lease this time, for some
> reason. So it's working again. I'll do a tcpdump next time, if I see the
> problem again, and hopefully that will tell me what's going on.
>
>
I do not know if this is the case, but ISP's usually record its
customers MAC address which is universally unique. Maybe, just maybe,
when you switched from your tp-link router to direct wan link, the ISP
machine noticed that there was an unknown MAC attempting to connect and
refused connection. Then your dhcp discover packets would reach ISP
hardware, but would not receive any responses.
BTW, you should notice that dchp communications are not held with the
same machines when you have a direct link as opposed to routed link.
When routed through some gateway, you have two sets of dhcp ISP <-->
router <--> pc.
Reply to: