Re: stale connections, keepalive?
Tomasz Sterna writes: > See io.keepalive [1][2] options. > Setting this up will flush single whitespace character over the wire > when the connection dangs idle. This triggers the TCP layer connection > validation. I set this up as: check every 300 close connections idle for 86400 (1d) send keepaliave after 14400 (4h) I realized I was seeing the problem on my other server too, just less (because I usually don't use my phone to it). I'll see if this resolves the issue. (My phone getting a wakeup every 4h is going to be zero compared to what happens in between, I think.) signature.asc Description: PGP signature
Re: stale connections, keepalive?
W dniu 29.08.2016, pon o godzinie 12∶41 -0400, użytkownik Greg Troxel napisał: > dropping idle connections from its NAT table without > > telling anyone, so later when mobile network closed a connection it > > silently dropped RST packets not knowing who to NAT them to. [...] > Are you saying that a cell provider tracks TCP state and when the > data connection is lost sends RST packets for open connections? I am blissfully oblivious to inner workings of wide area switching networks, but it sure looked like so when I was investigating the dangling connections issue. And a quick look at PDP_context[1] gives impression that it has specific knowledge of the established connections. [1] https://en.wikipedia.org/wiki/GPRS_core_network#PDP_context -- /o__ (_<^' All generalisations are dangerous, including this one. signature.asc Description: This is a digitally signed message part
Re: stale connections, keepalive?
Tomasz Sterna writes: > jabberd2 has support for application layer keepalives. > > See io.keepalive [1][2] options. > Setting this up will flush single whitespace character over the wire > when the connection dangs idle. This triggers the TCP layer connection > validation. Great - thanks very much for that pointer. > Having said that, I am running my server without both application layer > and TCP keepalives turned on and see no issues with dangling > connections. I run two jabberd2 servers. One of them is not behind a buggy firewall and does not have dangling connections. However, I'm not sure anyone is using a phone. > But.. I had them a lot, when my server was behind a buggy Cisco router > doing NAT. It was dropping idle connections from its NAT table without > telling anyone, so later when mobile network closed a connection it > silently dropped RST packets not knowing who to NAT them to. This was > causing a lot of dangling connections on my server. This is probably more or less the issue, and if so I can't fix it. Are you saying that a cell provider tracks TCP state and when the data connection is lost sends RST packets for open connections? I hadn't realized that, but it seems obviously sensible if a little bit of a layer violation. signature.asc Description: PGP signature
Re: stale connections, keepalive?
Christof Meerwald writes: > On Sun, Aug 28, 2016 at 02:13:34PM +0200, Tomasz Sterna wrote: >> W dniu 27.08.2016, sob o godzinie 14∶55 -0400, użytkownik Greg Troxel >> napisał: >> > should jabberd2 force TCP keepalive on? >> I'm not sure whether it is possible. >> At least on Linux it is a system-wide setting and requires root to >> change. > > Are you sure? There appear to be some socket options that can be set > for each socket: > > http://www.tldp.org/HOWTO/html_single/TCP-Keepalive-HOWTO/#setsockopt I'm not running Linux, so we're talking more or less about what POSIX specifies for the BSD sockets interface. But, that page describes in the SO_KEEPALIVE case exactly the traditional BSD socket option for keepalive, which I suspect dates from about 4.2BSD but my memory of the late 80s is now a bit fuzzy. So yes, I meant to have a way to enable keepalive via SO_KEEPALIVE on all sockets. But that's not really the right thing. Tomasz's point about Linux and system-wide setting is probably about what the default value is if a program doesn't ask for keepalives. OS X has a sysctl for this. NetBSD doesn't; it's up to the program, as it was historically. On the system in question, it is surely behind a buggy firewall. However, that's beyond my control. It's interesting that this doesn't show up, because I would expect the mobile to lose the data connection and fail to close the TCP connection fairly often. Arguably I have a system-wide problem, not a jabber problem. But still, given that clients just vanish, it seems like there should be some mechanism for connections to get cleaned up. I will check out the application-level keepalive. What I think I want is that for a connection from a client, if there has been no traffic in or out for 24h, to send a space. That will break the stale connections after a day, and it should not cause any additional traffic on real connections. For now I can just send a keepalive every 24h, and that's close enough. signature.asc Description: PGP signature
Re: stale connections, keepalive?
W dniu 28.08.2016, nie o godzinie 22∶45 +0200, użytkownik Christof Meerwald napisał: > > I'm not sure [...] > > Are you sure? [...] 😄 -- /o__ (_<^' One good turn deserves another.
