Layer 2 MTU issure

[Jia Hao]

As the Pic below, It says that C1 can send the packet to C2, and the SW's port 2 would not do the fragment, but I still don't get it.

I thought MTU liked  the size of the pipe, if set the MTU = 1514, it means that the pipe size is 1514, every frame bigger than 1514 should not pass through.

And would the layer 2 switch check the FCS field in layer 2 frame ?

[Joseph W. Doherty]

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Posting

Yes, the picture says that, but that doesn't guarantee the picture is correct.

What it shows, if the (Juniper?) EX4200 supports, is poor practice, i.e. having (it appears) two ports on the same switch with the same VLAN with different MTUs.

I would expect a switch to drop a too large MTU frame on ingress or (L2) egress, but perhaps an EX4200 has some "quirk" that it doesn't enforce port MTU, for (L2) egress, if the frame is already within the VLAN.

[Jia Hao]

Hi Joseph,

I just want to know how does the switch process the packet when the packet is bigger than the MTU of the switch's interface.

From this Pic, it appears that the switch would forward the frame and don't check the MTU in the egree interface.