Host Migration

thumb|300px|right|Examples of Host Migration succeeding. Notice how these host migrations occurs after high lag situations rather than the host leaving.

Host Migration is a new feature in Call of Duty: Modern Warfare 2 designed to attempt to continue a game in the event the host player leaves. It was announced in a pre-release trailer that demonstrated the system.

Overview
The Host Migration system is included to address the rampant problem in the previous games where if the host either yielded an unsavory connection or left the game entirely, the game would come to an end with the "Host Ended Game" message. Host Migration had already been a feature in the Halo games as far back as Halo 2, and only became possible since the upgrade to the Call of Duty engine made it possible to implement for Modern Warfare 2.

In the event that either of these two scenarios occur, the game will come to a halt and the words "HOST MIGRATION" will appear in the upper left, along with a message saying that a certain % of packets are sent. Then, a new host gets picked, and if all goes smoothly, a 5-second countdown timer will begin to resume play. If Host Migration occurs due to an unsavory connection to the host then that player will be kicked once host migration is completed.

Limitations
The Host Migration system is merely an attempt to establish a new host in order for the game to continue on. Due to the complex nature of attempting to connect to a new host, the Host Migration may or may not be able to work. Success rate is typically higher for situations where the host leaves the game (where the connection goes smoothly), but in other cases (usually when Host Migration is triggered because of lag problems), the server may simply time out. Also, the Host Migration can only work when the host selects "Leave Game" - exactly what would bring up Host Ended Game in the previous games. If the host quits any other way, i.e. dashboarding, signing out, unplugging, the game will server time out.

Smooth Host Migrations typically take no more than 10-15 seconds, others may take upwards of 30 seconds. If more than 45 seconds has passed, it doesn't look good for continuation of the game.

In addition, any killstreaks that are called in at the time the Host Migration occurs will be affected. This is most apparent for shorter ones like the Predator Missile, where, if being used when Host Migration occurs, will simply hit the ground and not do any damage. Other killstreaks will continue to be used up though for longer ones there may be some time left for them to do damage.