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- From: Ray Burkholder
- Date: Tue Jan 21 17:39:47 2003
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
> -----Original Message-----
> From: Mark J. Scheller [mailto:email@example.com]
> Sent: January 21, 2003 18:26
> To: firstname.lastname@example.org
> 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@example.com)