Many parts to discuss with linking cdjs and mixers together. Basically this is the process of connecting your cdjs and mixer to a network via ethernet cables. There are several features and advantages to doing this. I'll take it one section at a time.

Option 1: Linking 2 cdjs together with 1 Ethernet cable

This is the simplest way to create the network is to plug in one Ethernet (cat5) cable into each CDJ. Models that support this are the CDJ 900, 2000, 900NXS, 2000NXS and 2000NSX2. This allows you to plug in one USB into one CDJ. Then press the "LINK" option on the other CDJ. This will display all the contents of the USB on the 2nd CDJ and you can play tracks over the "linked network".

Advantages: 

• Shared History and Playback
• Play all tracks only using 1 USB
• Use beats and cue point markers on some models of CDJ for both decks

Option 2: Linking 2 or more CDJS via Ethernet Router/Switch/Hub

This method you will need to connect each CDJ with a separate ethernet cable to your router/switch/hub. This will also allow you to connect the mixer to the router for additional features. If you use a wireless router, this also unlocks additional features with rekordbox and phones/tablets. You can also connect a laptop via ethernet and use the Rekordbox function on the CDJS that support that option, such as the 900NXS or 2000NXS. 

Tag DJ Sets:
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Linking provides some more flexibility when tagging with another DJ. The first DJ can load a USB into deck A and then on deck B can click on LINK. Then the 2nd DJ can put a UBS into deck B and click LINK on deck A. I'll admit, it can get a bit confusing, but it does allow for pretty seamless tag sets and not having to load out USB sticks while tunes are playing, possibly ejecting the wrong one, etc.

Suggestions / Troubleshooting:

I suggest to always have a back up USB in each deck, just in case there is an issue with LINK status. If you see a message like "EMERGENCY LOOP" on one of the LINKED cdjs, it usually means that there some sort of interruption in the network. Could be a bad network cable, or the cable is loose or unplugged. Always bring back up ethernet cables as well. 

If you own or encounter a Pioneer DJM 750, 850, 900 NXS or 900 SRT, use the following guide to record your mixes via a USB cable. This is a big advantage for recordings live sets if you play on cds, vinyl or rekordbox and do not have Serato setup.

1. Download the driver / utility for each mixer from Pioneer:
www.pioneerdj.com/en-us/support/software/djm-750/
https://www.pioneerdj.com/en-us/support/software/djm-850/
​www.pioneerdj.com/en/support/software/djm-900nxs/
www.pioneerdj.com/en/support/software/djm-900srt/ 

2. Install each driver for either your mac or windows laptop

Once this has been done, you will be able to access each utility. Here is what it looks like for windows:​

3. Open utility for each mixer and set ALL channels to REC OUT. Also set the USB Output Level to -15dB

4. Download a program to record your mixes with. I use Audacity, which is FREE!
www.audacityteam.org/download/

​5. Install the program and connect the mixer to your laptop. You will need a USB A to  USB B cable. This is commonly referred to as a "usb printer cable". The square side of the usb cable will plug into the the usb port on the mixer, located in the top left of the mixer. Plug the other side into your laptop.

6. Open up Audacity and set the recording source to LINE IN - PIONEER DJM XXX

7. Click the record button. You should see music being recorded into the software. 

So a number of cool things about using this method to record:

• Everything is free! The mixer utilities and Audacity do not cost anything.
• You do not need a Serato box to record a live mix
• You do not have to make any configuration changes to the gear @ the club, just plug in the usb cable to the mixer! 

Here @ 404 Audio, we want to push relevant Atlanta Drum & Bass content to the masses. Our new "404 Audio DJ" section will post tips, tricks, how-to's and guides on various aspects of dj'ing. Countless times I have had to dig through manuals, posts on forums and websites to get the info I need on recording via usb on the DJm 900 or how to copy tracks from Serato to a usb stick, but still keep cue points / track analysis. We aim to bring this info together for local Atlanta local djs. Bookmark the site to keep up with our content! Big up!