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Re: Stumper
- From: William Warren
- Date: Tue Jan 21 17:45:26 2003
Most DSL providers want an MTU of 1492..also there are some issues with
older firmwares and some DSL providers. You may want to also check for
an updated firmware on the Linksys site.
Ray Burkholder wrote:
This might be an MTU setting issue. If pppoe, then on my Cisco stuff,
an MTU of 1492 (I think that is the right value) seemed to clear things
up.
Ray Burkholder
-----Original Message-----
From: Mark J. Scheller [mailto:[email protected]]
Sent: January 21, 2003 18:26
To: [email protected]
Subject: Stumper
I have run into a problem that has me completely stumped, so
I'm tossing it out to NANOG for some help.
Before I lay out the specifics, I'm not trying to point
fingers at any particular ISP or vendor here, but this
problem only exhibits itself in very specific configurations.
Unfortunately, the configuration is common enough as to get
unwanted attention from the higher-ups.
Here's the particulars:
Users that have Verizon DSL and a Linksys cable/DSL router
have difficulties accessing sites on my network -- whether
they are trying with http, https, smtp, pop3, ssh, ftp, etc.,
etc. Oh, but pings seem to be fine. Low latency, no loss.
This is true even for access to a server brought up in the
DMZ, to keep the firewalls out of the equation.
Doing some packet sniffing on the ethernet side of my router,
I could see specific http requests never showed up (and the
user saw the broken image icon). This was for an mrtg graph
page with +/- 30 images. I saw the request for almost all
the image files, save for one and the user reported the
broken image icon for the one. So this looks and smells like
a packet loss issue..... but who/where/how?
Taking the Linksys out of the pictures (connecting their PC
directly to the Verizon DSL modem) makes the problem go away.
These same users report no trouble whatsoever accessing many
other common sites across the internet.
Here's another interesting data point: when one user runs
Morpheus (on any machine in his home network) he then has
absolutely no problems accessing servers/services on my network.
Other users with Linksys routers and, say cable modem, do not
have this problem!
So I'm looking for some pointers. What could I have done to
my edge router (a Cisco 3640 if that helps any) that would
make it drop packets from Verizon DSL customers with Linksys
routers so long as they aren't running Morpheus?
Mark J. Scheller ([email protected])
--
May God Bless you and everything you touch.
My "foundation" verse:
Isaiah 54:17 No weapon that is formed against thee shall prosper; and
every tongue that shall rise against thee in judgment thou shalt
condemn. This is the heritage of the servants of the LORD, and their
righteousness is of me, saith the LORD.
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