An analyst is reviewing a packet capture from a large sample of mixed protocols. Which of the following tcpdump Berkeley Packet Filter (BPF) filters would reduce the data set to the information below?

'client' and 'server' are not valid BPF filter keywords, and '>' alone is not a recognized BPF comparison expression, making this an invalid and non-functional filter.

NTP operates over UDP on well-known port 123, so 'udp and port 123' uses valid BPF primitives to precisely isolate NTP packets and exclude all other traffic. This filter is syntactically correct and uses the standard tcpdump 'proto and port' construction to target the exact transport and port combination that NTP requires.

'not icmp and (src host 173.14.48.133)' would return all non-ICMP traffic from one IP address across every protocol and port, producing a far broader dataset than NTP traffic alone.

'ntp' is not a named protocol primitive in the BPF filter language; tcpdump does not recognize NTP by name, making this filter syntactically invalid and non-functional.