The Data Link Layer refers to “Layer 2″ in the OSI model. I assume when you say monitoring you mean a “Sniffer” to watch traffic at layer two. There are a number of them out there that are great and sometimes very useful, called wireshark it has both Windows and Linux distributions and really is quite powerful… and <b>FREE</b>!!!
This will capture and let you see traffic at layer 2 just fine. If you look at others out there you will likely want to be sure it operates in “Promiscuous mode”, basically if it doesn’t it will only allow you to see traffic sent to or from the device you are monitoring with. Most sniffer programs do offer this feature these days.
Keep in mind that a Switch will only send traffic to a port if the destination MAC address has been “seen” on the port, so you may need to configure the port as a monitor port to see all layer 2 traffic on monitor traffic with it, this in effect will make all traffic be sent to that port and I would recommend only using the port to monitor traffic and not for hosts on your network. You do not have to worry about this if you have a true network hub, but these are farther and fewer in between these days since switches are better at managing traffic than a hub.
Hopefully that helps, happy capturing!