** updating to correct this a bit **
adding to what Colin has said - indeed local probe request threshold (LPRT) of 10-15 is now the best practice - partly due to client match (CM), partly due to a change in the way LPRT is implemented in 6.3 which adds some extra margin that is used to block 802.11 auth frames (which can be too agressive on the fringe of coverage). In early 6.3 the margin was a little agressive, this was eventually fixed. In 6.4 this was split into a separate configuration called "auth request threshold" - but for the purpose of this post, let's leave that well alone, it's one of those "don't change unless advised to" items.
More often than not, people complaining of inability to associate - especially after upgrade to 6.3 or 6.4 for the first time - can be tied back to LPRT=25 or higher hanging around from previous attempts to solve roaming issues.
The other thing that changed was CM got better and handling various edge cases and quirk devices. It was common in some cases in 6.3 to have CM disabled and whatever value of LPRT configured.
Regretfully we have no easy way to handle this on upgrades, so let's put it in a list:
- AOS is < 6.x - LPRT whatever value was deemed workable
- AOS is 6.3.x (early) - best to either turn LPRT off or reduce it to 10-15 due to overzealous padding that got added. This was fixed (reduced) later - but it's still more agressive than older code
-
AOS 6.3.x (later) - if CM is on, 10-15... if CM is off, you could *maybe* go as high as 20, but 25 would still be considered a bit too high (since the padding is still there).
- AOS 6.4.x - same a 6.3.x (except more often than not, CM is still on)
>>>>> !! the short answer: 10 to 15 in all recent Aruba OS !! <<<<
10 or 15 ? make a judgement on density and whether you want the worst case client SNR to be 10 or 15. If AP density is good, make it 15; if sparse and maximal coverage is desired make it 10 etc. Can't make a call, don't know, unsure - then err on the side of caution and use 10.
regards
-jeff