2023-03-28

Network interface drop 1518 bytes Ethernet frame received from direct Ethernet link cable sent by tcpreplay. why?

I have two server linked to each other. I tried to send a pcap from one of the servers via direct link using tcpreplay command. The pcap contains an HTTP POST session which size of some frames is 1518 bytes [Ethernet header(14 bytes)][payload(1500 bytes)][fcs(4 bytes)], but the receiver server's interface drops packets with size over 1514 bytes.

Everything works correctly when I remove last 4 bytes(FCS) of all packets and send pcap. Or when I change MTU of the sender and receiver interface from 1500 to 1504. I can understand why the sender's interface MTU needs to be 1504. But why does the receiver's interface MTU need to be 1504? I expect the receiver's interface doesn't consider FCS bytes just like Ethernet header, because This is what is happening when the actual Ethernet frame of size 1518 is coming toward receiver's interface from internet.

Is there any difference between when the receiver consumes Ethernet frames from internet and when two servers are linked and one is sending to another by tcpreplay?

Thanks in advance.



No comments:

Post a Comment