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Internet Bottleneck somewhere in my network, how to find?

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Internet Bottleneck somewhere in my network, how to find?

SliderUK
Hi

I've just upgraded our modem to an ADSL2+ modem and connection rate has gone from 6mb to 16mb but yet i still download files at around 6mb within the network.

I've connected directly to the modem with my laptop and it does download at 16mb so there seems to be something in my network thats slowing the internet down.

Here is the network structure.

I've got the zyxel broadband modem going into a sonicwall firewall which is then going into a netgear gigabit switch. Plugged into the switch is an SBS2003 domain server and mainly xp clients. On SBS there is exchange configured.

The sonicwall has a bandwidth limiter which is switched off. I turned it on just to make sure it works and turned it off again. Apart from that i can't see where i'm getting the bottleneck.

Any help in finding the problem would me greatly appreciated.

Thanks

Clarifications

Rob Kuhn

Is there a proxy server in use?

Maybe a duplexing issue between the new modem and your firewall.

Try this: Put a 100MB or faster Ethernet switch inbetween the modem and your SonicWall. The switch can be a cheap/simple desktop switch. See if the transfer speed is where it should be.

I sort of ran into a similar issue when I bonded four T-1 lines. I wasn't getting the full bandwidth which was a duplexing problem/issue between the router and our Netscreen firewall (Juniper support was the ones who referred to it as a duplexing problem). Anyway, the switch "corrected" the duplex. Later I replaced the swtich with a L2 10/100/1000 MB switch just so I had some level of management.

HTH...

SliderUK

Hi thanks for your reply

I tried a switch between my firewall and the modem and it made no difference.
I also tried the switch between my firewall and the netgear switch. Also made no difference.

Just to note the SBS is also the DHCP and DNS server. Have i messed up the DNS somewhere? The client machines point to the SBS for DHCP and DNS. But they point to the sonicwall for the gateway. Is that correct or should i change it?

Thanks again for comments

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    0 Votes
    SliderUK

    Hi thanks for your reply.

    I tried a switch between my firewall and the modem and it made no difference.
    I also tried the switch between my firewall and the netgear switch. Also made no difference.

    Just to note the SBS is also the DHCP and DNS server. Have i messed up the DNS somewhere? The client machines point to the SBS for DHCP and DNS. But they point to the sonicwall for the gateway. Is that correct or should i change it?

    Thanks again for comments

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    0 Votes
    machinegun_kelly

    Maybe you got some cheap wire, weird, so your in full duplex only getting 6 MB, well if it makes no difference what switch you hook to the modem then the problem has to be in the modem or the wire, I haven't played around with ADSL modems in a while, call the Verizon tech support team, or who ever gave you the modem, I bet they can help you trouble shoot it. Sometimes these things are hard to troubleshoot online. I'm mostly the hands on type. When in doubt, swap it out!

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    1 Votes
    SliderUK

    After much troubleshooting yesterday i've found out that my sonicwall was causing the problem.

    I believe the sonicwall i got TZ-180 isn't quick enough to handle the throughput on higher broadband speeds. So i changed the security setting from "Maximum Security" to "Performance Optimized" and speeds are much quicker. They have jumped from being about 6mb to 12mb. But i do wonder how much i've compromised on my security by doing this.

    Anyone that can enlighten me on changing that security setting would be much appreciated.

    Thanks

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    the_harper

    Do a "shields up" scan and see what ports are exposed.

    https://www.grc.com/x/ne.dll?bh0bkyd2

    Also, when nobody else needs to use the network, unplug it from the internet, connect one computer and see what throughput you get. ADSL2+ will seldom give you the throughput that the connect speed indicates.

  • +
    0 Votes
    SliderUK

    Hi thanks for your reply.

    I tried a switch between my firewall and the modem and it made no difference.
    I also tried the switch between my firewall and the netgear switch. Also made no difference.

    Just to note the SBS is also the DHCP and DNS server. Have i messed up the DNS somewhere? The client machines point to the SBS for DHCP and DNS. But they point to the sonicwall for the gateway. Is that correct or should i change it?

    Thanks again for comments

    +
    0 Votes
    machinegun_kelly

    Maybe you got some cheap wire, weird, so your in full duplex only getting 6 MB, well if it makes no difference what switch you hook to the modem then the problem has to be in the modem or the wire, I haven't played around with ADSL modems in a while, call the Verizon tech support team, or who ever gave you the modem, I bet they can help you trouble shoot it. Sometimes these things are hard to troubleshoot online. I'm mostly the hands on type. When in doubt, swap it out!

    +
    1 Votes
    SliderUK

    After much troubleshooting yesterday i've found out that my sonicwall was causing the problem.

    I believe the sonicwall i got TZ-180 isn't quick enough to handle the throughput on higher broadband speeds. So i changed the security setting from "Maximum Security" to "Performance Optimized" and speeds are much quicker. They have jumped from being about 6mb to 12mb. But i do wonder how much i've compromised on my security by doing this.

    Anyone that can enlighten me on changing that security setting would be much appreciated.

    Thanks

    +
    0 Votes
    the_harper

    Do a "shields up" scan and see what ports are exposed.

    https://www.grc.com/x/ne.dll?bh0bkyd2

    Also, when nobody else needs to use the network, unplug it from the internet, connect one computer and see what throughput you get. ADSL2+ will seldom give you the throughput that the connect speed indicates.