Hi David IP_BIND_ADDRESS_NO_PORT did not fix your somewhat similar problem in your Haproxy setup, because all the connections are to the same dst tuple <ip, port> (i.e 127.0.0.1:ExtORPort). The connect() system call is looking for a unique 5-tuple <protocol, srcip, srcport, dstip, dstport>. In the Haproxy setup, the only free variable is srcport <tcp, 127.0.0.1, srcport, 127.0.0.1, ExtORPort>, so toggling IP_BIND_ADDRESS_NO_PORT makes no difference.
The following should help (unless found a bug in Linux): 1. Let tor listen on a bunch of different ExtORPort 2. Let tor listen on a bunch of ips for the ExtORPort (so we have #ExtORPort * #ExtOrPortListenIPs unique combinations) 3. Connect from different src ips (what you already implemented) 4. sysctl -w net.ipv4.ip_local_port_range="1024 65535" For 1 and 2 to make a difference, if you do a 3 (i.e bind before connect), you need IP_BIND_ADDRESS_NO_PORT enabled on the socket. Tor relays already connect to many different dstip:dstport pairs, so enabling IP_BIND_ADDRESS_NO_PORT should solve our problem. I rest my case ;) Best regards Anders Trier Olesen On Sat, Dec 10, 2022 at 5:41 AM David Fifield <da...@bamsoftware.com> wrote: > On Fri, Dec 09, 2022 at 09:47:07AM +0000, Alexander Færøy wrote: > > On 2022/12/01 20:35, Christopher Sheats wrote: > > > Does anyone have experience troubleshooting and/or fixing this problem? > > > > Like I wrote in [1], I think it would be interesting to hear if the > > patch from pseudonymisaTor in ticket #26646[2] would be of any help in > > the given situation. The patch allows an exit operator to specify a > > range of IP addresses for binding purposes for outbound connections. I > > would think this could split the load wasted on trying to resolve port > > conflicts in the kernel amongst the set of IP's you have available for > > outbound connections. > > This sounds similar to a problem we faced with the main Snowflake > bridge. After usage passed a certain threshold, we started getting > constant EADDRNOTAVAIL, not on the outgoing connections to middle nodes, > but on the many localhost TCP connections used by the pluggable > transports model. > > > https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/-/issues/40198 > > https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/-/issues/40201 > > Long story short, the only mitigation that worked for us was to bind > sockets to an address (with port number unspecified, and with > IP_BIND_ADDRESS_NO_PORT *unset*) before connecting them, and use > different 127.0.0.0/8 addresses or ranges of addresses in different > segments of the communication chain. > > > https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/-/merge_requests/120 > > https://gitlab.torproject.org/dcf/extor-static-cookie/-/commit/a5c7a038a71aec1ff78d1b15888f1c75b66639cd > > IP_BIND_ADDRESS_NO_PORT was mentioned in another part of the thread > ( > https://lists.torproject.org/pipermail/tor-relays/2022-December/020895.html > ). > For us, this bind option *did not help* and in fact we had to apply a > workaround for Haproxy, which has IP_BIND_ADDRESS_NO_PORT hardcoded. > *Why* that should be the case is a mystery to me, as is why it is true > that bind-before-connect avoids EADDRNOTAVAIL even when the address > manually bound to is the very same address the kernel would have > automatically assigned. I even spent some time reading the Linux 5.10 > source code trying to make sense of it. In the source code I found, or > at least think I found, code paths for the behvior I observed; but the > behavior seems to go against how bind and IP_BIND_ADDRESS_NO_PORT are > documented to work. > > > https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/-/issues/40201#note_2839472 > > > Although my understanding of what Linux is doing is very imperfect, my > > understanding is that both of these questions have the same answer: > > port number assignment in `connect` when called on a socket not yet > > bound to a port works differently than in `bind` when called with a > > port number of 0. In case (1), the socket is not bound to a port > > because you haven't even called `bind`. In case (2), the socket is not > > bound to a port because haproxy sets the `IP_BIND_ADDRESS_NO_PORT` > > sockopt before calling `bind`. When you call `bind` *without* > > `IP_BIND_ADDRESS_NO_PORT`, it causes the port number to be bound > > before calling `connect`, which avoids the code path in `connect` that > > results in `EADDRNOTAVAIL`. > > > > I am confused by these results, which are contrary to my understanding > > of what `IP_BIND_ADDRESS_NO_PORT` is supposed to do, which is > > precisely to avoid the problem of source address port exhaustion by > > deferring the port number assignment until the time of `connect`, when > > additional information about the destination address is available. But > > it's demonstrable that binding to a source port before calling > > `connect` avoids `EADDRNOTAVAIL` errors in our use cases, whatever the > > cause may be. > _______________________________________________ > tor-relays mailing list > tor-relays@lists.torproject.org > https://lists.torproject.org/cgi-bin/mailman/listinfo/tor-relays >
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