A little while back I posted an entry called MTU Vs MSS – Part One. At the time the plan was to follow it up with Part Two a short time later, however, here it comes over a year late :) I do apologise for that.
What prompted me to get back to writing Part Two was an e-mail from a reader who asked how I came to the conclusion that using the “ip tcp adjust-mss” command affects a SYN packet’s MSS regardless of whether it is applied to the inbound or outbound interface. The reader also asked if I have any links to documentation that describes this. The way in which I came to the conclusion was by labbing it up. Unfortunately though I do not have any documentation that backs me up.
This blog post will demonstrate the lab I used to come to the above conclusion.
Here is the topology that I used. I have marked each link with a letter to mark the points at which the proceeding packet captures were done. (Note that PC1 and PC2 are GNS3 routers with their icons changed).