61f6fbd0ce
Netstack always picks a random start point everytime PickEphemeralPort is called. While this is required for UDP so that DNS requests go out through a randomized set of ports it is not required for TCP. Infact Linux explicitly hashes the (srcip, dstip, dstport) and a one time secret initialized at start of the application to get a random offset. But to ensure it doesn't start from the same point on every scan it uses a static hint that is incremented by 2 in every call to pick ephemeral ports. The reason for 2 is Linux seems to split the port ranges where active connects seem to use even ones while odd ones are used by listening sockets. This CL implements a similar strategy where we use a hash + hint to generate the offset to start the search for a free Ephemeral port. This ensures that we cycle through the available port space in order for repeated connects to the same destination and significantly reduces the chance of picking a recently released port. PiperOrigin-RevId: 272058370 |
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| BUILD | ||
| ports.go | ||
| ports_test.go | ||