Different MTUs are displayed in the display isis interface command output on an S series switch

Q: In the display isis interface command output, why is the MTU on a broadcast network 1497 bytes whereas the MTU on a P2P network 1500 bytes?
A: By default, the physical MTU of Ethernet interfaces are 1500 bytes.
On a P2P network that has PPP enabled, the MTU is 1500 bytes in the display isis interface command output.
On a broadcast network, a 3-byte Local Link Control (LLC) field is added to the data field according to the 802.3 link protocol encapsulation format, and the value of the LLC field is FEFE03. Therefore, in IS-IS, the actual length of the data to be transmitted is 1497 bytes, which is 3 bytes shorter than the physical MTU.

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