The tracer has the ability to "skip" probes which fail with either AddressInUse or AddrNotAvailable errors.
This was added for TCP, where the the network layer performs a socket connect() after binding to the local socket address for each probe. By default for TCP tracing, the src port is set to be the sequence number and so if any of the src ports are in use (i.e. TIME_WAIT status) then the connect() operation will fail. The tracer can detect this situation and "skip" probes which cannot be bound.
Currently the tracer will do this if for both AddressInUse or AddrNotAvailable errors, however this is incorrect, it should only do this for the AddressInUse error.
macOS defines these errors as:
[EADDRINUSE] The address is already in use.
[EADDRNOTAVAIL] The specified address is not available on this machine.
Linux defines these errors as:
EADDRINUSE
Local address is already in use.
EADDRNOTAVAIL
(Internet domain sockets) The socket referred to by sockfd had not previously been bound
to an address and, upon attempting to bind it to an ephemeral port, it was determined that all
port numbers in the ephemeral port range are currently in use.
Testing on macOS confirms that only EADDRINUSE occurs in this scenario. Note that the stream socket sets SO_REUSEPORT which, on Linux, prevents this error from occurring. It does not appear to have any effect on macOS, the man page for setsockopt(2) says it should, but for UDP only:
SO_REUSEPORT allows completely duplicate bindings by multiple processes if they all set SO_REUSEPORT before binding the port. This option permits multiple instances of a program to each receive UDP/IP multicast or broadcast datagrams destined for the bound port.
The tracer has the ability to "skip" probes which fail with either
AddressInUseorAddrNotAvailableerrors.This was added for TCP, where the the network layer performs a socket
connect()after binding to the local socket address for each probe. By default for TCP tracing, the src port is set to be the sequence number and so if any of the src ports are in use (i.e.TIME_WAITstatus) then theconnect()operation will fail. The tracer can detect this situation and "skip" probes which cannot be bound.Currently the tracer will do this if for both
AddressInUseorAddrNotAvailableerrors, however this is incorrect, it should only do this for theAddressInUseerror.macOS defines these errors as:
Linux defines these errors as:
Testing on macOS confirms that only
EADDRINUSEoccurs in this scenario. Note that the stream socket setsSO_REUSEPORTwhich, on Linux, prevents this error from occurring. It does not appear to have any effect on macOS, the man page forsetsockopt(2)says it should, but for UDP only: