Blackhole Detection

Posted on 2005-03-02
Medium Priority
Last Modified: 2010-03-17
Blackhole Detection sounds like a good thing.  Who wants to be caught in a blackhole?
But System Mechanic Internet speedup turns that off.
What are pro/cons of Blackhole Detection?  (briefly)
Question by:raymm
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Expert Comment

ID: 13444739
Black hole detection provides a means for end devices to work efficiently over links with different MTU sizes.  For example, your local ethernet has an MTU of 1500 Bytes.  If there's a link somewhere along the line with some encapsulation that lowers the MTU to 1450 bytes, you'll end up with fragmented or dropped packets.  

A Black hole router is one that drops the packets without telling you.

With Black hole detection enabled, your end device will notice the loss of packets and start dialing down the MTU until packets get through.  This allows the end device to operate at max efficiency even though an intervening router may not be playing nicely.

Author Comment

ID: 13444757
Will it dial up after?

Author Comment

ID: 13444765
Would you turn it on if your main concern was speedy responsiveness from internet.

BTW, nicely explained.

Accepted Solution

jeopboy earned 2000 total points
ID: 13446278
the MTU will adjust to the maximum size packet that can get through the path between source and destination once it detects that packets are being lost.  Once that maximum size has been determined, it won't change.

As for responsiveness, it is going to depend on the application.  If you're online gaming, I think most of your packets are going to be small so you shouldn't need BHD.  For apps that use larger packets, without BHD, you could end up having problems with connectivity.  With it, you might have a bit slower response initially but should be good after that.

The other option is to lock in the MTU to some small size (576 is minimum) that should always get through.  This option will definitely slow things down for large file transfers but shouldn't have much effect on the more interactive apps like instant messenger or online gaming.

Good luck!

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