PPTP throughput very imbalanced with windows SBS 2003
Hello chaps What can cause imbalance in the throughput with PPTP VPN connections? I have this simple topology: PC1----SBS2k3 ^---PC2--^ PC2 is running Ixia Chariot performance console PC1 and SBS2k3 are the end points With raw ethernet performance is about 750mbps+ in either direction (test in single direction at any one time). When PC1 establishes a PPTP VPN to SBS2k3 the performance changes dramatically: Traffic from SBS2k3 to PC1 becomes 230mbps Traffic from PC1 to SBS2k3 is 106mbps Why this imbalance? There is no imbalance in raw ethernet tests only in PPTP VPN. So I tried another setup to rule out PC1: LAPTOP----SBS2k3 ^-----PC2----^ Results is very similar: Raw eth: SBS2k3 to LAPTOP is 655mbps Raw eth: LAPTOP to SBS2k3 is 853mbps PPTP: SBS2k3 to LAPTOP is 210mbps PPTP: LAPTOP to SBS2k3 is 108mbps Still sending from the pc to the server is similar - very imbalanced. So I tried taking out the server altogether and doing this using incoming connections on the laptop, so I had: PC1-------LAPTOP ^-----PC2----^ With PPTP VPN I get 188mbps in either direction. So it would appear on the face of it that sending TO the SBS2k3 is always slow but receiving from the SBS2k3 is always fast. WHY? And how do I fix this? What should I look out for? I looked (using wireshark) at the packets - the packet sizes were similar - there was no obvious MTU issues, both sides were sending 1437 byte payloads in IP when in 'full flow'. The only thing I did notice was the PC/Laptop advertises a PPTP window of 64 to the server and the server advertises 16384 to the client - but surely this should in fact IMPROVE sending to the server not degrade it? Oh and I ensured that things like virus scanning was turned off. *confused* Cheers Gareth
March 30th, 2010 6:30pm

Sorry I should have said that the pc and laptop are both using win7 pro
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March 30th, 2010 6:41pm

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