Unsolvable network problem on iMac with Mountain Lion

[d3marcus]

My network issues with my iMac is really driving me nuts.

I'm able to open two or three tabs in Chrome/Safari without any issues, but when I try to open more connections the response times are 30 seconds to several minutes. This occurs both on wifi and ethernet.

* I'm running the latest version of Mountain Lion with default network settings (DHCP).
* I've replaced the router but the problems are still there.
* I have a MacBook 13" Retina on the same network, with the same ML version without any network issues at all.
* I've tried to change the MTU size.
* I'm not running a torrent client or similar applications.

Grateful for all suggestions.

 

[fhall1]

What model iMac for starters? Connected via wire or wireless? More info is needed before anyone can start helping.

 

[BrianBaughn]

What model iMac for starters? Connected via wire or wireless? More info is needed before anyone can start helping.

This, and describe your networking setup (devices).

 

[d3marcus]

Sorry for not supplying all information.

It's a 12 Gb 27" iMac, mid 2011, running OS X 10.8.4. Connected with ethernet but I've tried wifi with same result. Wifi is now disabled so ethernet is the only network adapter running.

Ethernet settings:

IPv4: DHCP
IPv6: Automatic
DNS: No specific servers
WINS: Default (No specific servers)
802.1X: No profiles
Proxies: None
Hardware: Automatic

 

[fhall1]

What are you "wired" to? Direct to cable modem? router? if so, what brand/model router? cable, DSL, dish, dial-up?

 

[d3marcus]

Wired to an Asus router which is connected to a 100 Mbit optical fiber unit. I have tried with a D-link router also but the problems are identical. All other units (MacBook, iPads, PCs and so on) connected to the Asus router works without network issues so I think this is related to the iMac.