Network Troubleshooting Video Series

 

Episode 22, Segment 02 of 07

All Internet protocol packets include a provision for - "expiration" - if they spend too much time traveling around the Internet. This provision is useful because it is possible for misconfigured Internet routers to send packets in the wrong direction. When another router sends them back in the - "right" - direction, they can end up bouncing back and forth forever.

For example, suppose we have a single PC that wants to send a - "Ping" - packet to mit.edu as described in the prior movie on - "Ping".

 

Furthermore, suppose that one of the routers between our PC and mit.edu is misconfigured so that it doesn't know where mit.edu can be found, and it mistakenly sends our packet back in the direction from whence it came.

That packet would end up bouncing back and forth between two routers forever if no special provision had been made.

Accordingly, every Internet packet includes a field named "Time To Live", and each router that forwards a packet always decrements that value.

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Episode 22, Segment 03 of  07