I've been using Charter since I moved to Reno, given my great experience
with Road Runner in New York. I'm using a dual homed Solaris x86 box as
my Router / Firewall / nat box. This was routing between the two vlans I
setup on my 12 port Cisco Switch.
With Time Warner, I was able to get my Sol x86 box to pull it's IP
through the external vlan, but have not had great success doing that
with Charter. I'm not sure if the dhcpagent, on Solaris runs in
broadcast mode, but this makes me curious.
Charter's tech's weren't very helpful, and suggested the reason it
wasn't working is because the cable modem is caching the MAC of the
closest network device. (In my case the switch). I had been able to plug
the Sol x86 box directly into the cable modem, pull an IP address, and
then hook up the vlan's the way I wanted. But the configuration would
often loose it's mind when the lease expired, and I would be stuck
unplugging and replugging.
Finally I got frustrated, and just plugged the router directly into the
cable modem. I have had no issues since I did this.
-RYAN
On Sun, 2003-06-29 at 20:43, Ryan Finnie wrote:
> (Warning, long rant ahead)
>
> This weekend I dropped SBC and got Charter net access. Turns out my
> apartment was not on the line assigned to me, which warranted a service
> call to get it working, but that is outside the scope of this discussion.
>
> I currently use a Linksys WRT54G as my border router, which worked fine
> with SBC. But when I plugged it into the cable modem, it would not get an
> IP address. So I plugged my linux laptop in and ran dhcpcd, again,
> nothing. However, when I plugged in my Windows box, it would get an IP
> address. Then unplugging the windows box, plugging in the linksys, and
> cloning the windows box's MAC address would then work. So then I reset my
> cable modem and we were back to square 1, despite the MAC address still
> being cloned.
>
> A little background about DHCP: "Normal" operation dictates that the
> client broadcast a Discover packet, then the server sends an Offer
> directly to the client with the ip address being assigned. The client
> sends a Request to the server with that offered ip address, and the server
> responds with an ACK. However, there is a flag in the DHCP packet that
> can be set that says all communications should be done via broadcast. IE,
> the Discover, Offer, Request, and ACK packets are all addressed to
> ff:ff:ff:ff:ff:ff.
>
> That's the key. I don't know everything about Charter's network, but this
> is what I deduce from playing with Ethereal for an hour or so. Charter
> does "authentication" via DHCP. In an "unauthenticated" state, the only
> thing that the modem sees is ARPs and DHCP broadcasts. Everything else is
> filtered. However, once you are "authenticated" by grabbing an IP
> address, you are able to receive unicast traffic. That makes the
> broadcast bit in the DHCP packet essential. If the client requests a
> unicast reply, it will never see it.
>
> Looking at Ethereal dumps, it appears that my Linksys box does not set the
> DHCP broadcast bit. Neither does dhcpcd in its default mode (this can be
> changed by doing "dhcpcd -B eth0", at which time it works fine with
> linux). Windows's default mode is to set the DHCP broadcast bit.
> Unfortunately, it looks like the Linksys box does not have an option to
> set that bit.
>
> But, you may ask (more likely, you've stopped reading by this poing :),
> why is the linksys box able to get an IP address after the Windows box (or
> Linux with the -B option set in dhcpcd) gets and IP address first? Well,
> the "tunnel" is already up; the modem is now receiving unicast packets.
> The linksys box sends a DHCP Request, requesting a unicast reply. And
> Charter's DHCP server sends a unicast reply. And all is good.
>
> So what does a person like me do given this situation. Several things can
> be done:
> 1. Use Windows for the router.
> 2. Use Linux for the router, specifying the -B option to dhcpcd.
> 3. Use Linksys for the router, but doing #1 or #2 first to bootstrap the
> process.
> 4. Try to get ahold of an engineer at Linksys and suggest the ability to
> set a config option to specify what mode the dhcp client should use,
> broadcast or unicast.
>
> For now, I'm doing #3 and #4. That being said, what do the rest of you
> do? Does only the WRT54G do this? Did you just give up on using Linksys
> products with Charter? Is Charter's behaviour in this manner specific to
> my segment? Tell me your story, Charter users...
>
> Oh, and BTW, the performance seems good. Sunday evening and I'm getting
> about 750/115 on a 768/128k account, according to dslreports.com. YMMV.
>
> RF
> _______________________________________________
> RLUG mailing list
> [EMAIL PROTECTED]
> http://www.rlug.org/mailman/listinfo/rlug
_______________________________________________
RLUG mailing list
[EMAIL PROTECTED]
http://www.rlug.org/mailman/listinfo/rlug
