Well, the mtu size should normally be left at the default size of 1500. however, when encrypting traffic using IPSec you may want to lower your mtu to something like 1400. The reason is that IPSec encrypts and encapsulates the traffic which results in packet size being higher then 1500 bytes if you leave at the default size of 1500. This means that you are now transmitting two smaller packets instead of one. If you lower to 1400 then the packet, after encryption, will still be under 1500 and can be transmitted as one packet. This is an example of one of those rare instances when one might want to change the default mtu size.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...