Waht is the minimum MSS captured by wireshark?
I found out that the default MSS is 536 bytes, is that what the wireshark will capture or can be there be a lower MSS that gets captured?
I found out that the default MSS is 536 bytes, is that what the wireshark will capture or can be there be a lower MSS that gets captured?
The MSS has nothing to do with packet capture. MSS is a setting of the TCP/IP stack to define what the TCP segment size may be, so from 0 up to MSS. And Wireshark will happily dissect TCP packets with segments of any size.
And note that the "default" MSS is usually not the MSS that's used. An Ethernet packet has a maximum payload of 1500 bytes, an IPv4 header is a minimum of 20 bytes long, and a TCP header is a minimum of 20 bytes long, so the maximum TCP payload is 1500-(20+20) = 1460 bytes. That's the usual MSS that's negotiated.
Wireshark will, by default, capture the entire packet, however big that might be; as Jaap notes, that is not affected by the MSS.
While it looks like a MSS value is been negotiated, it is actually announced (advertised) in each of the two flows individually, instead of being negotiated.
Sidenote: This can lead to problems when routes are assymetrical over links with different MSS adjustments due to different MTU sizes or different amounts of encapsulation of each link.
Please start posting anonymously - your entry will be published after you log in or create a new account.
Asked: 2022-04-20 19:29:57 +0000
Seen: 489 times
Last updated: Apr 21 '22