Stumper

Tue Jan 21 22:35:31 UTC 2003

Could this be a packet size issue ?
You might try

ping -s

and see if, say, 1500 byte and 4500 byte packets get through.m

On Tuesday, January 21, 2003, at 05:25 PM, Mark J. Scheller wrote:

>
>
> 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 (scheller at u1.net)
>
>
>
                                  Regards
                                  Marshall Eubanks

T.M. Eubanks
Multicast Technologies, Inc
10301 Democracy Lane, Suite 410
Fairfax, Virginia 22030
Phone : 703-293-9624       Fax     : 703-293-9609
e-mail : tme at multicasttech.com
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