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Can anyone explain to me how the Hold Queue works, and what it's default settings should be?  What does the hold queue do, and what are it's benefits.

Here's how we have it setup:

 hold-queue 500 in
 hold-queue 1200 out

Lets say it's on a serial interface of a full T1.  Also would the hold-queues change for interfaces that are not set to full T1? (maybe decrease the amount, etc.).

Just curious.



RE: Hold-Queue

The hold-queue is simply a place where it holds packets while one is being transmitted out the interface.  And no the queue does not change with the bandwidth.  It is however possible to change the size of the queue manually if needs be, but usually not recommended.


RE: Hold-Queue

Would there be any noticeable impact on an interface by removing the hold-queues that we already have setup?  I'm looking at this from an ISP standpoint trying to see which way would benefit the customer (or hinder them with incorrect settings).  I have no problem removing our hold-queues but I want to make sure we aren't going to run into any issues by doing this (increased router CPU utilization, performance degradation, etc.).

Right now we have many many serial interfaces setup with hold-queues on each one.  If there isn't a reason for them I'd like to remove them (or adjust them to proper values).


RE: Hold-Queue

Hold Queues are absolutely neccesary.  If 2 packets enter the router at the same time destined out the same serial interface, the router can only send one at a time.  Of course, in real time, it only takes a few milliseconds to send the packet, but if there are no hold queues, the second packet would be simply dropped, cause the router has no where to store it thereby causing the sending end to retransmit and thereby 1/2ing the speed of the link.  Now that is only for 2 packets.  Say you have 60 packets headed out the same interface, that means 59 of them would drop and need to be retransmitted.

Dumping hold queues is a bad idea.  Just leave them the way they are.


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