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Strange issue browsing when router put into place:

Posted on 2006-05-31
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Last Modified: 2010-04-17
Coming in on the backend of a problem that another guy was working on.  Here is situation:

Remote office with VPN (just GRE tunnel) going back to headquarters.  DSL connection going into router, where pppoe is setup with correct authentication and standard config taken straight from Cisco sight (and used in other locations for this customer, where everything is working hunky-dory).  Nat is basic, and looks correct, and there are only three routing statements.  A default going out the DSL line, where nat is on the outside interface (ie dialer in this case).  Also routes for central company location going over tunnel interface.  

Okay, now the weirdness.  I can sit on a PC at the central company and telnet to this router fine.  The strange bit has been all of a sudden the PCs cannot browse on the Internet to certain sites.  Don't believe it to be DNS, because the name resolves, the page just gets stuck.  That being said, I did manage to load logmein on a remote PC there (with users assistance), and my logmein session works really well, no strange speed issues, etc.

The other guy said he has run adware removal.  I'm going to try going to Trend Micro this morning.  The wrinkle (I'm told), is that when you take the router out of the picture, everything apparently works fine going to the Internet.  They have tried multiple routers as well.  

Any suggestions?  I'm not in the office yet, but I will be this morning.  So if you guys need to see router config I can do that.  
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Question by:neowolf219
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lrmoore earned 2000 total points
ID: 16800354
DSL line sounds like a MTU issue. PPPoE adds 8byte overhead and packets get fragmented.
Set DSl interface to MTU 1492 from default 1500 ??
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by:neowolf219
ID: 16800736
yeah, did that.  

i'm starting to really think this isn't a routing issue.  matter of fact, i'm almost positive it isn't.  

Just really weird stuff, where I can browse to www.logmein.com or www.cnn.com, but I can't get to www.msn.com, www.windowsupdate.com, or www.espn.com.  It gives me a white screen, and then when I wait it just pops up with links to that page, if anything.  

I've run through Trend Micro, checked the host file to make sure nothing got hijacked.  Totally stumped.  waiting on a guy to get on site, and I'm going to get him to plug the workstation straight into the DSL line.  

If you can think of anything else, let me know.  I'll post when I know more.  
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by:neowolf219
ID: 16802630
okay, something new.

Under the DSL modem (Bellsouth), if I do straight PPPoE there, plug it into the LAN switches, everything works like a champ.

Once I switch it over to bridge mode to have the router in place, it stops working.  Same issue, some websites I can get to, some I can't.

This is something with the DSL modem. Any thoughts.
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by:neowolf219
ID: 16803182
well, this is really interesting.  I actually had to go under the network adapter in the registry, then add an MTU D-Word value, and set it up as 1492.  

So lrmoore, you basically were right on, it just didn't make sense, as I've never had to do that on the NIC (and yes, scouts honor, that mtu is setup as 1492 on the dialer interface on the router).  But it is working now.  
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by:lrmoore
ID: 16804333
Sometimes..... if icmp is not allowed in the firewall (unreachables) then the PathMTU Discovery mechanism breaks in Windoze systems.. go figure...
Glad you got it working!
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by:neowolf219
ID: 16807565
Yeah, I tried it both with my router mitigation ACL in on the outside, and then I also took it off (we were in "punt mode", as I like to call it, you know, were theory is thrown out the window and you are just trying random things that don't make sense).  

Still scratching my head as to why that is happening, don't know.  If I come across any revelations I'll let you know.  
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