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My Sonicwall TZ200 is Killing My Internet Speed

By steve - Posted on 22 October 2013

I have a fairly sophisticated setup for my Sonicwall TZ200. I have 3 internet connections: 1) A traditional T1 @ 1.544mbps, 2) AT&T DSL at 6mbps, and 3) Comcast at 24mbps.

I've played with various load balancing schemes, but what has worked best, until recently, is a simple failover system where all my outbound traffic goes out and comes in via Comcast, my email traffic uses the T1, and the AT&T connection acts as a backup connection.

When I tried some percentage based stuff, it worked, but when some users reported the connections being slow, it was always hard to tell who (which connection) was responsible.

Anyway, things were going swimmingly until just a few weeks ago when users began complaining about connections being really slow.

We had been making some changes recently because the TZ200 had been freezing up and Sonicwall had me redo the entire configuration by hand because of that. That issue turned out to be because we were using the DHCP server in the Sonicwall and that didn't cooperate with our Sonicpoint setup. The Sonicpoint would freeze up and stop shipping traffic for no reason. As soon as we moved the DHCP server to a Windows Server and shut that down, our Sonicpoint problem went away.

(I digress again...)

Anyway, after that, things had gone very well until, suddenly a few weeks ago, the performance on the wired network was just horrible! We are supposed to be getting 24mbps down from the Comcast connection, but we were lucky to get 10% of that. Our ping times were horrible at 500 to 1000 msec instead of the usual 20 or 30 msec.

Well, as sometimes happens, it took a lot of serious investigation to finally figure out what was wrong...

First, I figured out that the connection between the Comcast modem and the Sonicwall TZ200 wasn't quite right. The Comcast modem was set to NOT auto-negotiate, but the Sonicwall WAS set to auto-negotiate. As soon as I set the Sonicwall to Full duplex-100mbps, my ping times dropped right to the desired sub-20msec times.

I was still only getting 3 or 4 mbps, though!

I knew it wasn't Comcast (all though other times it had been) because I could hook up directly to the modem and get the desired speeds. I could also hook up a wireless access point to the Comcast and get fast access there, too.

I googled all over the place and tried lots of different things including removing all other devices, swapping cables, making sure the DPI services were off, making sure the extra secruity services were off (we don't subscribe), making sure the bandwidth management services were off (never turned them on!), etc., but not of that made a difference. Nor did rebooting devices or putting switches between the various connections.

Finally, I was reading yet another article about people having problems with Sonicwall performance and I read about gigabit switches not working well with non-auto-negotiated settings on other devices. I didn't think much about it because my Sonicwall is a 100 and my Comcast is a 100, so no problem.

As I was later doing some wire testing, I found out something odd. I knew my direct-to-Comcast wireless (our guest network) was getting getting better than 10mbps, but I didn't release my inside the network wireless was also!


It meant that the problem was not in the Sonicwall nor in the Comcast (after fixing the ping issue), it meant the problem was between the Sonicwall and my network! What??

I have a gigabit switch as the backbone of my network and that is what is hooked up to the Sonicwall. It should be working flawlessly, in fact, I had moved my Sonicwall cable from one port to another just to make sure it wasn't a port problem.

So, it seems what was happening was that the Sonicwall was set to 100 and not auto-negotiate. The Dell gigabit switch was unable to deal with that (a common problem apparently with gigabit copper) and was probably negotiating the connection down to 10mbps or less.

As soon as I changed the Sonicwall LAN connection (X0 in my case), my speeds INSTANTLY jumped to full 24mbps with Comcast.


Problem solved!

That was it, after all that work. Just make sure your Sonicwall stuff is connected to the Gigabit switch with auto-negotiate and you should be just fine. I'm guessing that perhaps the Dell switch WAS set to 100 at some point, but it lost that setting. Or it could be that it just got out of spec enough that having things set to 100 just freaked it out :-)


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