[nSLUG] Eastlink cable modem access

Jon me at jonwatson.ca
Thu Jan 31 14:02:34 AST 2008


Oops.

Link to RFC 2131: http://www.faqs.org/rfcs/rfc2131.html

On Jan 31, 2008 2:02 PM, Jon <me at jonwatson.ca> wrote:

>
>
> On Jan 31, 2008 1:51 PM, Gerald <linux at zdoit.airpost.net> wrote:
>
> > Jon wrote:
> > . . . .
> > > Interesting. Granted, I don't spend a lot of time watching DHCP logs,
> > > but I would think that the second example is more indicative of a
> > > 'normal' DHCP request as it is a broadcast request on port 67. This is
> > > designed to hit any DHCP server on the network in the hopes that it
> > will
> > > give out an address.
> > >
> > > Given that a computer without an IP address cannot communication on a
> > > TCP/IP network. I can't see how a DHCP request to a specific address
> > > (like  in your first snippet) would succeed. Perhaps it's a refresh
> > > request in that the interface already has an IP assigned to it and can
> > > therefore query a specific DHCP server.
> > >
> > > Curious...
> > >
> > > Jon
> >
> > Jon,
> >
> > I wasn't looking at the logs until I noticed a connection from my router
> > to the 10.6.x.x address on a DHCP port. Then I started looking at the
> > logs.
> >
> > My understanding of the DHCP protocol is it can/must ask first for a
> > renewal from the same DHCP server that offered the address to be
> > renewed. That leads to requests to a specific address instead of the
> > 255.255.255.255 address.
> >
>
> Hmm...dunno.
>
> RFC 2131 doesn't state that.
>
> Section 3.1 deals with client broadcast requests and section 3.2 deals
> with client specific requests (as in the client is asking for a specific IP
> address). Both these sections list step 1 as 'the client broadcasts as
> DHCPREQUEST message...' which would seem to preclude the specification of a
> DHCP server as a valid step in the DHCP process.
>
> However, that's a big document and I've spent all of 2 minutes with it so
> who knows.
>
> I know none of this helps with your problem. Thanks for humouring my idle
> curiousity.
>
> Jon
>
>
>
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