Ethernet frame and MTU

Here is story about MTU.

 

1. Etherent frame size (without 802.1q) = 1518 Bytes

Destination mac(6) + source MAC(6) + type(2) + data(1500) + FCS(4)

 

2. Etherent frame size (with 802.1q) = 1522 Bytes

Destination mac(6) + source MAC(6) + type(2) + 802.1q(4) + data(1500) + FCS(4)

 

3. IP header size?

20Bytes

 

4. TCP header size?

20Bytes

 

5. UDP header size?

8Bytes

 

6. VXLAN header size?

8Bytes

 

7. What is MTU?

MTU = IP packet (which is included TCP header)

 

8. MSS?

MSS = MTU – (IP header + TCP header) = 1500 – 40 = 1460 (in general)

 

9. When you ping with -f bit, packet size did get over 1472 bytes, why?

MSS = 1472 = MTU – (IP header + ICMP header) = 1500 – (20 + 8) = 1472 bytes.

 

10. Best MTU for VPN?

Being updated