Re: Wireless router losing Internet connection (DHCP problem)

[POSTED TO alt.internet.wireless - REPLY ON USENET PLEASE]

In <fahs421oosu5lgj4cetdf4k7t9ddtlfr61@xxxxxxx> on Tue, 25 Apr 2006 09:12:38
-0700, Jeff Liebermann <jeffl@xxxxxxxxxxxxxxxxxxxxxx> wrote:

John Navas <spamfilter0@xxxxxxxxxxxxxx> hath wroth:

DEAD END: Hawking support was a dead end -- there was nothing related to the
problem in the scripted answers that had been provided to the telephone
support person (who had poor English and was probably located in India).
(...)

Sigh. Where to begin?

Buying a better router. :) But the Hawking can't be returned (packaging
discarded), and I'm trying to do this for a friend without having to spend any
more money. Oh well. I've now faxed a support request to Hawking (for
whatever good that will do).

Instant bottom line: Possible defective DHCP client in the Hawking
HWR54G.

That's been my guess as well. But if that is the case, I'm surprised at not
seeing more complaints on the Internet.

Power cycling the hardware generates a new DHCP lease request. Leaving
it disconnected for a while resets the ARP table in the CMTS. Comcast
does NOT register the MAC addresses of the client and has an unusually
short ARP table persistance of about 15 minutes to allow juggling
hardware.

Don't think so. Here's why:

* I'm pretty sure the router is using its hardware (MAC) address as the
identifier when requesting a DHCP lease -- that's the easiest way to generate
a unique identifier, and is why MAC address cloning can be used to take over
an existing lease.

* On basic cable modem service, Comcast will only hand out one client IP, so
it won't hand out a second DHCP lease while a first lease is still active. It
does this by comparing the identifier of a new DHCP request to the identifier
of any existing lease.

* Comcast will hand out a new DHCP lease if the cable modem (not the router)
is unplugged for less than a minute (not 15 minutes). This is presumably
because the CMTS triggers immediate expiration of any existing DHCP lease when
the cable modem disappears or is re-registered.

DOCSIS 1.1 CPE specs at:
| http://www.cablemodem.com/downloads/specs/SP-CMCI-I09-030730.pdf
says in Sect 2.1:
The cable modem MUST be capable of filtering all broadcast traffic
from the local LAN, with the exception of DHCP (as identified by
the destination port number in the UDP header) and ARP packets.

Translation: The cable modem should block broadcasts but pass
directed DHCP requests (as found when using a DHCP relay agent).

Just means the cable modem will bridge/relay DHCP Discover requests by
client(s).

Hawking undoubtably gets it right for DHCP lease requests or it would
not have an initial IP address, but probably screws it up for DHCP
renewals.

That's been my guess as well.

The big question is whom to blame. It could be that the database on
the CMTS is loading the cable modem with garbage.

Unlikely. That would probably cause a directly attacked PC to fail the same
way, which isn't happening.

t could also be
that the Hawking HWR54G has a problem with its DHCP client
implimentation.

More likely. Or at least some sort of compatibility issue.

Sniffing the traffic and waiting for the Hawking
HWR54G to request a lease renewal does not sound like a productive
exercise.

I agree.

Therefore, I suggest replacing the Hawking HWR54G with
something else for a while and see if the problem magically goes away.

If I don't get some help from Hawking, that's what I'll have to do.

The 4 days is the typical Comcast DHCP lease interval.

Yep.

There are also others with similar and recent DHCP lease renewal
problems:
[SNIP]

Yep.

Also, for fun, try this free DHCP query tool:
| http://www.weirdsolutions.com/weirdSolutions/files/products/desktopSoftware/desktopQueryTool/querytool_free.exe
I'm not sure if till show anything because it can't generate lease
renewal requests, but it might be interesting to see what it returns
anyway.

It would have to be run on a PC directly attached to the cable modem and
configured with a fake static configuration (so any new DHCP lease request
isn't rejected by Comcast), and I personally doubt it would show anything
interesting with regard to the router lease renewal problem. Also, it fails
to create a System Restore point when installing, and tries to remove a system
DLL when uninstalling. Color me unimpressed.

--
Best regards, SEE THE FAQ FOR ALT.INTERNET.WIRELESS AT
John Navas <http://en.wikibooks.org/wiki/FAQ_for_alt.internet.wireless>
.

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