I am having trouble finding specifics on this topic. The following articles touch on MTU calculation but doesn't specify exactly how PAN calculates MTU "on the wire".
This states you can configure standard MTU as 1500 plus 1518 L2 on the wire. This is a typical Cisco response where they have a hidden buffer of up to 24 bytes to cover the uneducated Windows user that only knows the number 1500. But then the article goes on to cover jumbo frames with ambiguous language -
PAN-OS 5.0, 5.1:
With jumbo frames is disabled, the maximum supported MTU is 1500 bytes at layer 3, and 1518 bytes at layer 2.
With jumbo frames enabled, the maximum supported MTU is 9192 bytes for both layer 3 and layer 2.
PAN-OS 6.0 and newer: With jumbo frames are enabled, the default value will be 9192 bytes. The maximum supported MTU is 9216 bytes:
I don't see how it's possible to have the same maximum MTU value at both Layer 3 and Layer 2. If you set a Layer 3 interface MTU to 9216, how do you account for the L2 Header, any 802.1q tagging or the FCS? Is there a hidden buffer like in Cisco IOS that accounts for these larger values or does PAN calculate MTU like Juniper? The following article covers this very well in terms of Cisco vs Juniper.
The only hint I could find that makes me lean towards a hidden buffer is the following PAN support article on MRU. But this only defines a hidden buffer for ingress packets, not egress.
Scratching my head at this point. Any help, information, articles on this topic would be appreciated.
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