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I have a stupid question, there are at most 65536 ports and some are not usable. There is also a file descriptor limitation. How to have that many concurrent co

I have a stupid question, there are at most 65536 ports and some are not usable. There is also a file descriptor limitation. How to have that many concurrent connections? https://unix.stackexchange.com/questions/84227/limits-on-the-number-of-file-descriptors https://unix.stackexchange.com/questions/84227/limits-on-the...

chmod775 8y ago
There are at most 65536 ports per remote IP. TCP connections are basically identified with an (ip, port) tuple. Also you can set the file descriptor limits to whatever you want.
- LinuxBender 8y ago
  To further clarify, even if you only had 1 host behind a proxy, you can create multiple listeners for that application on different ports or IP's. I do this for a few of my servers to avoid fin-wait / time-wait assassination attacks. i.e. have apache listen on 127.0.0.* and set up ifcfg-lo-range with IPADDR_START=127.0.0.10 IPADDR_END=127.0.0.99 PREFIX=8 CLONENUM_START=10 Or have the server behind haproxy listen on a few hundred ports.
- Florin_Andrei 8y ago
  > TCP connections are basically identified with an (ip, port) tuple. I believe the full identifier is a quad: (source ip, source port, dest ip, dest port).
  - mrkstu 8y ago
    Also note that DNS will load balance the IP presented. For instance 'dig'ing yahoo.com gives me the following: ;; ANSWER SECTION: yahoo.com. 92 IN A 72.30.35.9 yahoo.com. 92 IN A 98.138.219.231 yahoo.com. 92 IN A 72.30.35.10 yahoo.com. 92 IN A 98.137.246.7 yahoo.com. 92 IN A 98.138.219.232 yahoo.com. 92 IN A 98.137.246.8 So you can now multiple the quad by the number of public IPs you load up into your DNS record.
- zokier 8y ago
  Aren't TCP connections more accurately identified by (srcip, srcport, dstip, dstport) tuple? This is somewhat significant as you can easily have tons of IPs in a single box.
  - toredash 8y ago
    Correct
  - guiambros 8y ago
    Yes, but after the initial syn/ack, the daemon will allocate an outgoing port number for the connection. So if you have a single IP address and a burst with hundred of thousands of requests, you will run into problems..
  - chmod775 8y ago
    Yes, but local port and IP are usually fixed when running a HTTP server (unless you're binding to multiple IPs on one machine).
- dorfsmay 8y ago
  > Also you can set the file descriptor limits to whatever you want. Isn't limited by the amount of memory?

chmod775 8y ago

There are at most 65536 ports per remote IP. TCP connections are basically identified with an (ip, port) tuple. Also you can set the file descriptor limits to whatever you want.

LinuxBender 8y ago
To further clarify, even if you only had 1 host behind a proxy, you can create multiple listeners for that application on different ports or IP's. I do this for a few of my servers to avoid fin-wait / time-wait assassination attacks. i.e. have apache listen on 127.0.0.* and set up ifcfg-lo-range with IPADDR_START=127.0.0.10 IPADDR_END=127.0.0.99 PREFIX=8 CLONENUM_START=10 Or have the server behind haproxy listen on a few hundred ports.
Florin_Andrei 8y ago
> TCP connections are basically identified with an (ip, port) tuple. I believe the full identifier is a quad: (source ip, source port, dest ip, dest port).
- mrkstu 8y ago
  Also note that DNS will load balance the IP presented. For instance 'dig'ing yahoo.com gives me the following: ;; ANSWER SECTION: yahoo.com. 92 IN A 72.30.35.9 yahoo.com. 92 IN A 98.138.219.231 yahoo.com. 92 IN A 72.30.35.10 yahoo.com. 92 IN A 98.137.246.7 yahoo.com. 92 IN A 98.138.219.232 yahoo.com. 92 IN A 98.137.246.8 So you can now multiple the quad by the number of public IPs you load up into your DNS record.
zokier 8y ago
Aren't TCP connections more accurately identified by (srcip, srcport, dstip, dstport) tuple? This is somewhat significant as you can easily have tons of IPs in a single box.
- toredash 8y ago
  Correct
- guiambros 8y ago
  Yes, but after the initial syn/ack, the daemon will allocate an outgoing port number for the connection. So if you have a single IP address and a burst with hundred of thousands of requests, you will run into problems..
- chmod775 8y ago
  Yes, but local port and IP are usually fixed when running a HTTP server (unless you're binding to multiple IPs on one machine).
dorfsmay 8y ago
> Also you can set the file descriptor limits to whatever you want. Isn't limited by the amount of memory?