Networking issues

[David A. Bandel]

On Fri, 26 Sep 2003 13:25:43 -0700 (PDT)
Brad De Vries <devriesbj at yahoo.com> wrote:

> I have a network of WinXX PC's with a single Linux box
> acting as the gateway/firewall/dhcp server/e-mail
> server/etc.  My Linux box connects to the ISP via 128K
> ISDN dial-up line (too far away for DSL and cable is
> N/A).
> 
> When I first connect the Linux box to the ISP, I can:
> 1) Use the Linux box to traceroute to everything (the
> ISP blocked ICMP so I can't ping outside their
> network).
> 2) Use the Linux box to browse the web (using Lynx).
> 3) Use the WinXX PC's to browse the web to "some"
> sites (google, domains hosted by ISP, etc.)
> 
> When I first connect the Linux box to the ISP, I can
> not:
> 1) Use the WinXX PC's to tracert beyond the first two
> hops, Linux box is first and the ISP's router is the
> second.
> 2) Use the WinXX PC's to browse the web to anything
> "big" such as Yahoo!, ABCNews, FoxNews,
> WeatherChannel, etc.
> 
> After a while (sometimes 5 minutes, sometimes 20 or
> more) I begin to lose some functionality.  Such as
> traceroute from Linux to the world or pinging the
> ISP's router, etc.  The ISDN Terminal Adapter (i.e.,
> modem) sends the requests, the SD light goes on, but
> never receives a reply, no RD light.
> 
> I've been experiencing this problem for the last week
> to 10 days.  Does anyone have any thoughts as to what
> might be the cause?  I've replaced some hardware
> including the hub and cabling and I've tried using an
> analog modem but the same problem persists.  The Linux
> box has been running for a very long time without any
> changes.  (For those of you heavily in the Windows
> world, a user rebooted the Linux box the other day to
> see if it would fix the problem but it, obviously,
> didn't.)

Sounds like a typical broken DNF issue.  Try lowering the MTU on the
Linux box' connection to your ISP and see if that helps:

ifconfig <dev> mtu 296

If not, does your ISP permit multiple systems behind a NAT box?  There
are ways to detect nat'd systems, and he _might_ be blocking them (would
be the first time I've heard of this happening though).

Ciao,

David A. Bandel
-- 
Focus on the dream, not the competition.
		Nemesis Racing Team motto
GPG key autoresponder:  mailto:david_key at pananix.com
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