What version are you running? There should be no 63 peer limit since v0.8, or I've missed something weird.

Thank you for your answer.
I'm running the current latest release, 0.10.2 Linux x64 on a Debian Wheezy

What errors are you seeing then?

When I exceed 63 peer, for each connection I got the following error =>

[IABET] 21:07:38 INFO: Established secure connection to XXXXXXX-XXXXXXX-XXXXXXX-XXXXXXX-XXXXXXX-XXXXXXX-XXXXXXX-XXXXXXX at [ServerIP]:[Port]-[ClientIP]:[Port]
[IABET] 21:07:38 INFO: Connection to XXXXXXX-XXXXXXX-XXXXXXX-XXXXXXX-XXXXXXX-XXXXXXX-XXXXXXX-XXXXXXX closed: EOF

Is there another log that I can give to you ?

Anything on the other side?

On the "client" side, I get this message =>
[2BNTH] 21:14:39 INFO: Established secure connection to [NodeID Server] at [ClientIP]:[Port]-[ServeirIP]:[Port]
[2BNTH] 21:14:39 INFO: Connection to [NodeID Server] closed: xdr read: EOF

Are both sides running the same version?

Yes, we're all running on 0.10.2

@calmh why was there a 63 limit in the first place?
I found this which is interesting:

Folder Structure:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Length of ID                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                                                               /
\                     ID (variable length)                      \
/                                                               /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Number of Devices                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/                                                               /
\                Zero or more Device Structures                 \
/                                                               /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


struct Folder {
    string ID<64>;
    Device Devices<64>;
}

!!!

That's the cause, for sure. That shouldn't be there any more, that limit on number of devices should be removed (and the error message should be fixed so we can figure out why when similar things pop up in the future).

(As for why; in the early days, internally the index was based on a bitfield stored in an uint64. Bit zero was the local host, the rest of the bits where remote nodes. Checking for availability was a simple AND operation.)

Resolved by #886.

(Note to self: remember to investigate and fix that error message. "EOF" sucks to signal a protocol error.)

Okay, i'm glad you guys have find out the problem. Thanks a lot for your reactivity.
Until it's released, I'll run 2 syncthing simultaneously on 2 differents ports, dividing the peers.
It's a good workaround for now.

I guess you could compile master branch and tell us if its fixed :)

... or just download a copy from http://build.syncthing.net/job/syncthing/

Yes! good point

Hi guys, I just tried the latest dev-build, and the problem is still there =/
Still can't have more than 63 peers.

Are all nodes using the latest dev build?

No, the other nodes use the 0.10.2 release.
We deal with people with very a low understanding of the situation, they only use the update from the Web GUI

I guess you'll have to wait till the next release, as this is a two way issue.

Okay no problem, thank's for you answer !
We will continue to use 2 different Syncthing until then.

Just to clarify - this is in theory fixed in the current 11.0 beta6 or 10.3? I don't see this ticket number referenced in any of the release notes.

check this one: #886

This was fixed in v0.10.3.