4 ms·

I thought you can make only 65k connections per port because of TCP limitations.

by ValleZ 8y ago

hathawsh 8y ago
The limit is 65k connections per client IP address, limited by the number of available ports on the client. You can theoretically accept connections from all possible client IP addresses simultaneously. This means that in order to test 1M simultaneous connections, you would need to use at least 16 client IP addresses. Probably more.
- e-r-a-n 8y ago
  And most linux distros limits the ephemeral range even further to about 30K ports If you take a deeper look, the solution uses Docker to connect clients from different network namespaces to mitigate this
- athenot 8y ago
  As a fun aside, you can do this on localhost by defining additional addresses tied to the loopback interface: 127.0.0.2 127.0.0.3 etc. I once had to test a piece of software that identified its connections by the source IP, so I had a script to create thousands of loopback addresses within 127.0.0.0/8 and then run against that software and verify the connections were doing what they were supposed to do. (This was on Mac OS X.)
sempron64 8y ago
The limit is only between a single client and server ip, since there can only be up to 65k source port/ip pairs (assuming the destination port is a single port, which it seems to be in the code examples). So if there are multiple client ips it seems like it's not an issue. https://stackoverflow.com/a/2332756 https://stackoverflow.com/a/2332756
foobiekr 8y ago
Deep down, the key for a connection is the concatenation of SA DA SP DP. DA and DP are constant for a given service in the simple case and the others are 4 octets [although not all of it usable] for IPv4 and 2 octets (for port).
shereadsthenews 8y ago
This comment appears routinely on HN. I'd love to find out how something so basic about TCP came to be so widely misunderstood.
- wmf 8y ago
  Because almost everyone tests with one client IP and one server IP.
kondro 8y ago
An open connection is identified by all 4 values of the unique tuple source IP, source port, destination IP, destination port.
lessclue 8y ago
UNIX sockets can help.
- e-r-a-n 8y ago
  How?

I thought you can make only 65k connections per port because of TCP limitations.

by ValleZ 8y ago

I thought you can make only 65k connections per port because of TCP limitations.

The limit is 65k connections per client IP address, limited by the number of available ports on the client. You can theoretically accept connections from all possible client IP addresses simultaneously. This means that in order to test 1M simultaneous connections, you would need to use at least 16 client IP addresses. Probably more.

e-r-a-n 8y ago
And most linux distros limits the ephemeral range even further to about 30K ports If you take a deeper look, the solution uses Docker to connect clients from different network namespaces to mitigate this
athenot 8y ago
As a fun aside, you can do this on localhost by defining additional addresses tied to the loopback interface: 127.0.0.2 127.0.0.3 etc. I once had to test a piece of software that identified its connections by the source IP, so I had a script to create thousands of loopback addresses within 127.0.0.0/8 and then run against that software and verify the connections were doing what they were supposed to do. (This was on Mac OS X.)

sempron64 8y ago

The limit is only between a single client and server ip, since there can only be up to 65k source port/ip pairs (assuming the destination port is a single port, which it seems to be in the code examples). So if there are multiple client ips it seems like it's not an issue. https://stackoverflow.com/a/2332756 https://stackoverflow.com/a/2332756

foobiekr 8y ago

Deep down, the key for a connection is the concatenation of SA DA SP DP. DA and DP are constant for a given service in the simple case and the others are 4 octets [although not all of it usable] for IPv4 and 2 octets (for port).

shereadsthenews 8y ago

This comment appears routinely on HN. I'd love to find out how something so basic about TCP came to be so widely misunderstood.

wmf 8y ago
Because almost everyone tests with one client IP and one server IP.

kondro 8y ago

An open connection is identified by all 4 values of the unique tuple source IP, source port, destination IP, destination port.

lessclue 8y ago

UNIX sockets can help.

e-r-a-n 8y ago
How?