Which feature mitigates fragmentation issues caused by endpoint hosts?
A. TCP Flow Control
B. ICMP DF bit
C. PMTUD
D. TCP MSS
Which feature mitigates fragmentation issues caused by endpoint hosts?
Which feature mitigates fragmentation issues caused by endpoint hosts?
A. TCP Flow Control
B. ICMP DF bit
C. PMTUD
D. TCP MSS
The keyword here is “caused by endpoint hosts”. That tells me that it is TCP MSS, not PMTUD.
C
TCP MSS takes care of fragmentation at the two endpoints of a TCP connection, but it does not handle the case where there is a smaller MTU link in the middle between these two endpoints. PMTUD was developed in order to avoid fragmentation in the path between the endpoints. It is used to dynamically determine the lowest MTU along the path from a packet’s source to its destination.
PMTUD is only supported by TCP and UDP. Other protocols do not support it. If PMTUD is enabled on a host, and it almost always is, all TCP and UDP packets from the host will have the DF bit set.
B
The way MSS now works is that each host will first compare its outgoing interface MTU with its own buffer and choose the lowest value as the MSS to send. The hosts will then compare the MSS size received against their own interface MTU and again choose the lower of the two values.
Scenario 2 illustrates this additional step taken by the sender in order to avoid fragmentation on the local and remote wires. Notice how the MTU of the outgoing interface is taken into account by each host (before the hosts send each other their MSS values) and how this helps to avoid fragmentation.
In Scenario 2, fragmentation does not occur at the endpoints of a TCP connection because both outgoing interface MTUs are taken into account by the hosts. Packets can still become fragmented in the network between Router A and Router B if they encounter a link with a lower MTU than that of either hosts’ outbound interface.
https://www.cisco.com/c/en/us/support/docs/ip/generic-routing-encapsulation-gre/25885-pmtud-ipfrag.html#anc3
C.
TCP MSS – feature, that mitigate only for Tcp fragmentation issue. – in the question nothing about TCP.
So only C, seems are corrct.
C
PMTUD was developed in order to avoid fragmentation in the path between the endpoints. It is used to dynamically determine the lowest MTU along the path from a packet’s source to its destination
I agree. Whereas PMTUD was developed to manage fragmentation in the path between endpoints, TCP-MSS manages fragmentation issues at the end points themselves
D
https://www.cisco.com/c/en/us/support/docs/ip/generic-routing-encapsulation-gre/25885-pmtud-ipfrag.html#anc3
The TCP Maximum Segment Size (MSS) defines the maximum amount of data that a host is willing to accept in a single TCP/IPv4 datagram. This TCP/IPv4 datagram might be fragmented at the IPv4 layer. The MSS value is sent as a TCP header option only in TCP SYN segments. Each side of a TCP connection reports its MSS value to the other side. Contrary to popular belief, the MSS value is not negotiated between hosts. The sending host is required to limit the size of data in a single TCP segment to a value less than or equal to the MSS reported by the receiving host.
correct, its D