MTU on port with tagged VLAN

Hi Carl,

I do not want fragments!!!

That will slow down my traffic. 

BTW., only routers can fragment frames, not L2 switches. I do not use the GS748T as a router, but purely as a L2 switch. 

I also doubt that the L2+ GS748Tv5 (=static L3 switch) can fragment. Can you show me in the manual where it describes that?

The switch manual only states:

• Maximum Frame Size - The maximum ethernet frame size the interface supports or is configured, including ethernet header, CRC, and payload. (1518 to 9216). The default maximum frame size is 1518 .

It does not mention VLAN tag, which is between ethernet header and payload. With a normal maximal payload of 1500, the frame size becomes  1522 for a VLAN tagged ethernet frame.

Why is this not mentioned in the manual?

See this reference from Cisco:

http://www.cisco.com/c/en/us/support/docs/switches/catalyst-4000-series-switches/29805-175.html

This document discusses the support of varying Maximum Transmit Units (MTUs) on Catalyst 4000/4500 series switches 

"Standard Ethernet frame MTU is 1500 bytes. This does not include the Ethernet header and Cyclic Redundancy Check (CRC) trailer, which is 18 bytes in length, to make the total Ethernet frame size of 1518. In this document, MTU size or packet size refers only to Ethernet payload. Ethernet frame size refers to the whole Ethernet frame, including the header and the trailer. Baby giant frames refer to Ethernet frame size up to 1600 bytes, and jumbo frame refers to Ethernet frame size up to 9216 bytes."

So there is a standard MTU size of 1500 of the L3 payload of an ethernet frame. That makes the Ethernet Frame Size 1518 for non-VLAN frames and 1522 for VLAN-tagged frames. 

Does Netgear mean MTU=Ethernet Frame Size?

What happens if the switch receives or sends a frame that is larger than the configured MTU for a port, drop it?

Should the MTU be set to 1522 for ports that carry VLAN tagged frames, in order to prevent dropping frames?

Regards,

Frits.