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On my network, my edge-router, a windows 2003 r2 server router with all the latest updates, will drop packets, but only under specific circumstances. I have troubleshot and isolated it down to the most simple configuration i can. There is NO NAT involved. Only fully-public IP addresses. No Firewalls are running either, all ahve been disabled. no packet filters on any interfaces anywhere either.

I have a single Windows XP virtual machine and my edge-router(the windows 2003 r2 server, and also a virtual machine) running on a windows 2008 x64 r2 system (running virtual server 2005 as i dont have Intel-VT compatible chip yet).

The edge router can access any external http site just fine, no issues. However the windows XP machine is only able to access certain sites. These work: www.google.com www.txstate.edu www.workintexas.com www.thedailywtf.com . These Dont: www.yahoo.com www.utexas.edu en.wikipedia.org slashdot.org www.bing.com.

I have removed all possibility of DNS issues by connecting with net-cat from the XP box and sending GET /\r\nHost: \r\n\r\n and that connection replicates the issue as well.

The network setup: My statically assigned IP block: x.x.x.168/29

     DSL Modem  -----PPPoE Connection---- x.x.x.169[EdgeRouter]
     [EdgeRouter]x.x.x.170 -----Virtual Ethernet----- x.x.x.174 [Test2]

Test2's Default gateway is x.x.x.170 and test2 can ping any and every valid, accessible, public IP address with no packet loss what-so-ever. If i connect directly over PPPoE from test2 (the XP box) everything works just fine...

Im at my wits end, i have NO IDEA whats causing this.

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1 Answer 1

I resolved my issue. Turns out it wasnt restricted to just HTTP, but thats where it would manifest most obviously. The issue was related to the drop in MTU caused by PPPoE and its resulting impact on TCP MSS. The MSS' negotiated by the internal endpoint and external hosts did not take into account the reduced MTU available to the network and as such would exceed it causing the packets to drop.

I resolved this by on my OpenBSD router setting up a scrub PF rule to limit the MSS.

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