The Path Maximum Transmission Unit (PMTU) is the maximum size of the entire IP packet including the IP header, UDP header, and UDP <del> payload.  The UDP payload includes the QUIC packet header, protected payload, and any authentication fields.  The PMTU can depend on path characteristics, and can therefore change over time.  The largest UDP payload an endpoint sends at any given time is referred to as the endpoint's maximum packet size. </del> <ins> payload.  The UDP payload includes one or more QUIC packet headers and protected payloads.  The PMTU can depend on path characteristics, and can therefore change over time.  The largest UDP payload an endpoint sends at any given time is referred to as the endpoint's maximum datagram size. </ins> An endpoint SHOULD use DPLPMTUD (dplpmtud) or PMTUD (pmtud) to determine whether the path to a destination will support a desired <del> maximum packet size without fragmentation.  In the absence of these mechanisms, QUIC endpoints SHOULD NOT send IP packets larger than the smallest allowed maximum packet size. </del> <ins> maximum datagram size without fragmentation.  In the absence of these mechanisms, QUIC endpoints SHOULD NOT send datagrams larger than the smallest allowed maximum datagram size. </ins> <del> Both DPLPMTUD and PMTUD send IP packets that are larger than the current maximum packet size, referred to as PMTU probes.  All QUIC </del> <ins> Both DPLPMTUD and PMTUD send datagrams that are larger than the current maximum datagram size, referred to as PMTU probes.  All QUIC </ins> packets that are not sent in a PMTU probe SHOULD be sized to fit <del> within the maximum packet size to avoid the packet being fragmented or dropped (RFC8085). </del> <ins> within the maximum datagram size to avoid the datagram being fragmented or dropped (RFC8085). </ins> If a QUIC endpoint determines that the PMTU between any pair of local and remote IP addresses has fallen below the smallest allowed maximum <del> packet size of 1200 bytes, it MUST immediately cease sending QUIC </del> <ins> datagram size of 1200 bytes, it MUST immediately cease sending QUIC </ins> packets, except for those in PMTU probes or those containing CONNECTION_CLOSE frames, on the affected path.  An endpoint MAY terminate the connection if an alternative path cannot be found. Each pair of local and remote addresses could have a different PMTU. QUIC implementations that implement any kind of PMTU discovery <del> therefore SHOULD maintain a maximum packet size for each combination of local and remote IP addresses. </del> <ins> therefore SHOULD maintain a maximum datagram size for each combination of local and remote IP addresses. </ins> A QUIC implementation MAY be more conservative in computing the <del> maximum packet size to allow for unknown tunnel overheads or IP </del> <ins> maximum datagram size to allow for unknown tunnel overheads or IP </ins> header options/extensions. 14.2.1. Path Maximum Transmission Unit Discovery (PMTUD; RFC1191, RFC8201) relies on reception of ICMP messages (e.g., IPv6 Packet Too Big <del> messages) that indicate when a packet is dropped because it is larger than the local router MTU.  DPLPMTUD can also optionally use these messages.  This use of ICMP messages is potentially vulnerable to off-path attacks that successfully guess the addresses used on the </del> <ins> messages) that indicate when an IP packet is dropped because it is larger than the local router MTU.  DPLPMTUD can also optionally use these messages.  This use of ICMP messages is potentially vulnerable to off-path attacks that successfully guess the addresses used on the </ins> path and reduce the PMTU to a bandwidth-inefficient value. An endpoint MUST ignore an ICMP message that claims the PMTU has <del> decreased below the minimum QUIC packet size. </del> <ins> decreased below QUIC's smallest allowed maximum datagram size. </ins> The requirements for generating ICMP (RFC1812, RFC4443) state that the quoted packet should contain as much of the original packet as