The test process

• If we issue two bind(2) system calls to two sockets with the same port number, will it go successful, or either of/both of them fails?
• For the failure case, does the ordering of bind(2) matter?
• If the two bind(2) attemps go successful, which socket will get incoming traffic?
• For TCP case, does the order between bind(2) and listen(2) affect the behavior?

The list of addresses to be tested with bind(2) are as below:

wildcard: :: and 0.0.0.0

 

loopback: ::1 and 127.0.0.1

 

IPv4 mapped wildcard and loopback:

::ffff:0.0.0.0 and ::ffff:127.0.0.1

invalid address:

::ffff:0.0.0.1 and 0.0.0.1. Their goal is to test common programming mistakes in the implementation.

When two sockets become ready after bind(2), bindtest attempts to send some packets to see which socket accepts which packets. For UDP cases, it tries to issue sendto(2) for each address bound to each socket, and for the additional address if specified by the -o option. For TCP cases, the program tries to issue connect(2) for one destination specified by the -1, -2, or -o IPv4address options. -1 and -2 let bindtest connect(2) to the address that the program has used for bind(2). With -o, bindtest connects to the address specified by the extra argument, IPv4address. Note that the options -1 and -2 are meaningful only when -t is specified.

When the -o IPv4address option is specified, the address can be any valid IPv4 address in theory, but, for the testing purpose, the address is meaningful only when it is an IPv4 address assigned on the testing node itself.

The -l option is meaningful only when the corresponding socket is TCP. It specifies bindtest to issue bind(2) for both two sockets first, and then to issue listen(2) for the sockets. Normally, the program calls the two calls for the first socket, and then calls them for the second socket. This option exists because there is an operating system that behaves differently for those two cases.

Summary output

starting tests, socktype = SOCK_DGRAM, SO_REUSEADDR, V6ONLY
wild4 wild6 loop4 loop6 wildm loopm onem one4 wild4: x o[--1x] o[-21x] o[-21x] ?2(49) ?2(49) ?2(49) ?2(49) wild6: o[--2x] x o[-20x] o[-20x] ?2(49) ?2(49) ?2(49) ?2(49) loop4: o[1-2x] o[1-0x] x o[120x] ?2(49) ?2(49) ?2(49) ?2(49) loop6: o[1-2x] o[1-0x] o[120x] x ?2(49) ?2(49) ?2(49) ?2(49) wildm: ?1(49) ?1(49) ?1(49) ?1(49) ?1(49) ?1(49) ?1(49) ?1(49) loopm: ?1(49) ?1(49) ?1(49) ?1(49) ?1(49) ?1(49) ?1(49) ?1(49) onem: ?1(49) ?1(49) ?1(49) ?1(49) ?1(49) ?1(49) ?1(49) ?1(49) one4: ?1(49) ?1(49) ?1(49) ?1(49) ?1(49) ?1(49) ?1(49) ?1(49)

bindtest will make a two set of socket(2) and bind(2). The first set is presented on the lefthand side. The second set is presented above the table.

o

The second bind(2) attempt was successful after the first bind(2). “o” is followed by three letters enclosed in square brackets. The first letter shows the test result after sendto(2) to the first socket address (listed on the topmost row). The second letter shows the test result after sendto(2) to the second socket address (listed on the leftmost column). The third letter shows the test result after sendto(2) to the IPv4 additional address, when specified by the -o option, through an AF_INET socket. The fourth letter shows the test result after sendto(2) to the additional IPv4 address, when specified by the -o option, through an AF_INET6 socket using IPv4-mapped IPv6 address.

-

The address is wildcard (:: or 0.0.0.0) and no attempts were made to test send/recv behavior.

0

None of the sockets received the packet.

1

The first socket received the packet.

2

The second socket received the packet.

b

Both sockets received the packet. This result is not supposed to happen, but exists just in case.

x

The attempt of sendto(2) failed. UDP cases only.

c

The attempt of connect(2) failed. TCP cases only.

The meaning of the result table is the same for TCP cases, whereas only one of the three possible cases should be tried in a single execution of the test.

x

bind(2) failed for the second set, with EADDRINUSE.

!1

socket(2) failed for the first set. Normally you will not see this, unless you run bindtest on IPv4-only/IPv6-only kernel. Will be followed by errno(2) in paren.

!2

socket(2) failed for the second set. Normally you will not see this, unless you run bindtest on IPv4-only/IPv6-only kernel. Will be followed by errno(2) in paren.

?1

bind(2) failed for the first set. Will be followed by errno(2) in paren.

?2

bind(2) failed for the second set, with some error other than EADDRINUSE. Will be followed by errno(2) in paren.