Put switch between ISP's modem and my firewall then bandwidth drops dramatically

[users keep me busy]

ISP's modem: Telco 2141
that plugs directly into my firewall which is a SonicWall NSA 220.
Speeds are great, 100up/100down.

When I place a dummy, gigabit switch between the Telco 2141 and the firewall's WAN port, my speeds drop dramatically. Somewhere around 18down/15up.

The switches that I've tried: Netgear GS108, Netgear GS605v5 and Amped RTA15 (only using ethernet ports on back to bypass router, etc.) All have the same results but the speeds do vary slightly, however still much less than 100/100.

When the switch was installed between the modem and firewall, I assigned my laptop a static IP that was given to us by ISP and plugged directly into the switch (this bypasses my firewall) and my speeds were still degraded. I'm led to believe that the problem is with my ISP's modem and/or the switches that I'm using.

Can anyone offer some insight as to why or what is causing my bandwidth to drop so much after installing a dummy gigabit switch?

Many thanks in advance!

 

[bill001g]

Did you assign the same IP the firewall is using on its wan port and you did not unplug the firewall ?

You can not use the same IP on 2 devices you get massive strange issues including slow transfer speeds.

If you have 2 different IP from the ISP it should not have much impact. I would be guessing somehow you have a half duplex connection between the switch and the modem. That is not very common anymore since things autonegotiate better but if the ISP has set theirs to full duplex you will have to set yours to full duplex which may not be possible on some switches

 

[users keep me busy]

Thanks for your reply bill001g,

You raise an interesting point. I was using an IP that's part of the block assigned to my WAN port (although not used) and I will test a completely different IP.
I will also disconnect the firewall which will allow me to test from my laptop through the switch to ISP's modem without any interference from firewall.
Will have to do so after hours but will post back shortly.

 

[users keep me busy]

Speed negotiation was the answer and many thanks bill001g!
I set my laptop's NIC to match the speed setting of the ISP's modem (under the Advanced properties of NIC) and it worked flawlessly while plugged directly into the ISP modem.
When I put a dummy gigabit switch between, my speeds dropped.
Turns out I need a switch that can be configured to 100mb Full Duplex.
Any suggestions aside from Cisco?

 

[bill001g]

First is to find a simple managed switch. Then you are going to have to dig through the manual to see if it has that option not all do. You could I suppose find a used small 10/100 commercial switch and use it as a media converter with one port on 100full and the other on auto to connect to your gig switch. It will not hurt performance to have 2 switches and you can get older 10/100 cisco or hp commercial switches for very cheap since nobody wants 10/100 anymore.

 

[users keep me busy]

Went out and got me a D-Link DGS-1100-05 gigabit smart switch that allows me to specify the port speeds of each individual port.
Switch cost: $40
Will implement tonight, fingers crossed.

 

[users keep me busy]

Works perfectly well. Cannot thank you enough bill001g.