As mentioned, it's probably a DSL modem. As such, the modem may also be a router. Some routers can also block IRC traffic until you change the settings. You can check for the brand and name of your router and try setting it up for mIRC there. Normally that site doesn't explain actually *connecting* to a network, but you can at least see how to get into the settings from that site and then look around for something dealing with IRC.

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