RE: Slow Network Speed over WAN

Hi David,

Have a look to make sure you are not fragmenting encrypted packets on either
end of the tunnel. If the packets are put into the VPN or otherwise
encrypted, they'll grow, potentially pushing them past your MTU. This means
that they'll fragment as they are shipped into the WAN. This is further
complicated by Windowing as it allows more packets through before it
validates making the reassembly processor intensive. You can lose half of
your bandwidth ore more due to retransmits and the routing of nearly empty
fragments. This theorem is supported by the fact that wrenching up the
window size makes the problem less visible.

You could attack this by dropping the MTU on the servers or by forcing the
encryption after fragmentation. The latter option is done on your router (or
switch if you're running one of the big ones for IP distribution -- sup 720
or the like).

Finally, you might also look at your QoS -- it is possible that you are
being bumped in the transfer or aren't maintaining priority. Check this
both locally and as you enter the IP cloud.

Oh, and looking at SMB signing might also be worth while -- you can see a
30% overhead there.
--
Ryan Hanisco
MCSE, MCTS: SQL 2005, Project+
http://www.techsterity.com
Chicago, IL

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"David" wrote:

1. West Coast Site and Remote Site are on Gigabit Ethernet LAN with Gigabit
to the public Internet and are interconnected to each other by private IP
transport (Routed Gigabit). Both are connected directly to the external
router, bypassing the Firewall (Public IP addresses entered directly on the
Windows NIC). They each also have a second interface/NIC on our private LAN
(10.x.x.x IP range).
2. Each site has a Fibre-connected gigabit router, no rate limit set.
3. The servers can communicate with each other by either their public
interface or their private interface. The private interface uses the private
IP transport (effectively a site-to-site VPN), the Public interface uses the
internet. Both have the same performance.
4. Copies from the West Coast server to another in the same site happen at
the expected speed (20%-40% utilization of the max interface speed), the same
is seen at the remote site.
5. Any server in the West Coast site has the same performance limitations
when communicating with any server in the remote site.
6. When using some of the available network speed performance test
websites, I’ve gotten speeds of:
Download Speed: 201673 kbps (25209.1 KB/sec transfer rate)
Upload Speed: 18124 kbps (2265.5 KB/sec transfer rate)
Those speeds are representative of either site (when testing against a test
site geographically close).

Additional information: When I test using iPerf, I can see 30%-40% NIC
utilization when I adjust up the TCP window size. I can also see this
performance when using multiple simultaneous copy operations (either FTP or
Robocopy).

"Jian-Ping Zhu [MSFT]" wrote:
1. Please describe the detailed Network Topology.
2. Is there any routing/NAT devices between your two Windows Servers? If
yes, please check whether there are any bandwidth limitation policies set
on them.
3. Please tell me the way how these two Servers communicate with each
other. (Though VPN or WAN connection directly.)
4. Please test the copy speed between two Windows Servers in the same local
LAN and check whether the issue still occur.
5. Please choose a different Windows Server located in remote side and test
the copy speed between local site's Windows Server and remote site's
Windows Server via WAN connection.
6. Please try to download some big document from the internet on local
site's Windows Server and test the download speed.

.

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