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Strange network connectivity issues

I've ran into some weird problems that started to occur about 3 weeks ago. It seems that everyone in a specific subnet can only receive around 10-15Mbps of Internet connectivity. Yet, when I use my laptop I can continually get 70+Mbps, our internet link is a 100Mbit symmetric connection.

The only difference I see in these computers compared to my laptop is that the computers have been associated to an Active Directoy domain and have Symantec anti virus installed. I removed a computer from the domain and disabled Symantec and the connection rate of 10-15Mbps didn't improve. I am not using a proxy at this location.

So my question is, do you think this can be a network issue? If my laptop runs at full speed yet the computers don't when both devices are on the same switch, and I even swapped the computer with my laptop using the exact wire going to the punch down block, and my laptop still attains the 70+Mbps speed, could this be related to the network? Does anyone know if Active Directory could effect NIC settings that are reducing the speed?

Some more information about this link, it's using a GRE tunnel encapsulated with IPSEC. The MTU size on the tunnel is manually set to 1524 which cisco has told me before that this was too high. So I set it down to 1400 and when doing this I lost the ability to connect to some websites, like yet others would work. This change also further reduced the speed of the computers on the network. I'm trying to remember but i believe my laptop was unfazed by the change.

A packet capture showed many walls of TCP window full messages on the computers running slow yet I don't recall seeing any on my laptop's packet capture.

I appreciate any help!

Also, I need to do more testing but I did an iPerf test between a virtual server that was joined the the domain and a physical server not joined to the domain and the physical server had 4x the amount of bandwidth. I need to further test this though as the virtual servers are sitting on their own switch, tomorrow I'll plug my laptop into the switch and test from them to make sure there isn't an issue with them. I'm anxious to get to the bottom of this...

Community Member

The computer that runs slow

The computer that runs slow has a packet size of 1434 my laptop has a size of 1314 and runs a lot better. The tunnel is set to 1524, I tried to set the packet size to 1314 on the slow computer but a wireshark still shows that packets are 1434... doesn't seem like the Microsoft fix I ran took...

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