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Internet Speed drops with use of router?

I had an issue with cable provider having upgraded speeds, but as I was using an older 1721 router, I was unable get pass 10MBps. So obvious solution was to replace the 1721. However I have encountered a problem that is both mind boggling and intrigueing me. The cable modem is a Cisco 2100, when I directly connect using my laptop I can get 15-19MBps. When I connect any type of router or firewall, behind them I can only get between 1-4MBps. My first thought was maybe the 1721 was going bad? But testing between two LANs (i.e. laptop to another laptop) showed me this was not the case. Again simply limited by the 10MBps routing throughput.

So essentially if a PC is directly connected to modem, thus on same WAN subnet as the cable provider, I can get the higher speeds. If connected via router/firewall and on seperate subnet, speed drops too significantly. Same router shows the me that getting 1-4MBps is not a problem with the device itself.

Now I should mention, at moment I have not bothered to even consider anything in the config. Why? Because the config is a pretty standard one that I have in use on two other 1721....of which I do not have this problem (one if which I am in use with daily as it is connected to Wifi). So for learning and understanding purposes, I would love to know what could possibly cause such a significant drop in speed just being nothing more than1 more hop?

Edit: I should add even tried Sonicwall that was currently in use in another location that was getting about 15MBps from the internet provider, but here it is same speed of 1-4MBps.

2 REPLIES

Internet Speed drops with use of router?

Hello Sean:

This issue could be cause due to mismatch in speed and duplex of the media access layer.  For example, have you check if when you connect your PC directly it works at 100/10 / full duplex(I suppose you are using the ethernet port), now what if you connect the 1721 back again.  Is it getting the same speed and duplex?

If there is a mismatch, I suggest to hardcode speed and duplex in both devices.

Regards.

Wilson B.

Internet Speed drops with use of router?

Definitely check the router port facing the provider for errors, fragmentation, check things like MTU settings facing your provider


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