Peer exchange (PEX) is a feature of the BitTorrent peer-to-peer protocol which, like trackers and DHT, can be utilized to gather peers. Using peer exchange, an existing peer is used to trade the information required to find and connect to additional peers. While it may improve (local) performance and robustness—e.g. if a tracker is slow or even down—heavy reliance on PEX can lead to the formation of groups of peers who tend to only share information with each other, which may yield slow propagation of data through the network, due to the few peers sending information to those outside the group they are in.