print-autonomous-system-number-in-asdot-notation.md

Print Autonomous System Number in ASDOT notation

The ASN (Autonomous System Number, and you can think it as port number) will be outputted in ASPLAIN format by default. However, if -b option is specified (code is here):

	......
	case 'b':
		++ndo->ndo_bflag;
		break;
	......

The ASN will be displayed in ASDOT notation when the number is bigger than 65535 (code is here):

static char *
as_printf(netdissect_options *ndo,
          char *str, int size, u_int asnum)
{
	if (!ndo->ndo_bflag || asnum <= 0xFFFF) {
		snprintf(str, size, "%u", asnum);
	} else {
		snprintf(str, size, "%u.%u", asnum >> 16, asnum & 0xFFFF);
	}
	return str;
}