Networking and Traffic MTU
What is an MTU?
Maximum Transmission Unit (MTU) refers to the largest packet size that can be sent over a network without fragmentation. The standard MTU size for Ethernet networks is 1500 bytes.
What is a Jumbo Frame?
A Jumbo Frame is an Ethernet frame with a payload greater than the standard 1500 bytes.
Why Larger MTUs are needed?
Larger MTUs may be needed when using certain network protocols such as Dot1q Tunneling or QinQ services. These protocols add additional headers to the packet, which increases the overall packet size and reduces the available payload. By using larger MTUs, the network can still transmit the same amount of data in fewer packets, reducing overhead and increasing throughput.
Impact on Layer 2 and Layer 3 Performance
Using larger MTUs can improve performance at the Layer 2 and Layer 3 of the OSI model. At Layer 2, larger MTUs can reduce the number of packets needed to transmit the same amount of data, which reduces overhead and improves throughput. At Layer 3, larger MTUs can reduce the number of packets needed to transmit the same amount of data, reducing the load on routers and improving overall network performance. However, it’s also important to note that larger MTUs can also cause issues with some network devices that don’t support them and can cause fragmentation.
Fragmentation
Fragmentation is the process of breaking a large packet into smaller packets for transmission over a network that has a smaller maximum packet size than the original packet. This is typically done when a packet is too large to be transmitted over a network link that has a smaller MTU than the packet’s size.
Impact on Secure Traffic
Fragmentation can impact secure traffic like HTTPS in a few ways. First, fragmentation can increase the overhead of the network, which can slow down the overall performance of the network. Second, fragmentation can also increase the risk of man-in-the-middle attacks. Third, some security protocols like IPSec and SSL/TLS have a requirement for a certain level of MTU. Therefore, it’s important to ensure that the network is configured with the appropriate MTU size to avoid fragmentation and its potential impact on secure traffic.
Packet header with VLAN tag, payload etc
When a packet is transmitted over a VLAN, the VLAN tag is added to the packet as an additional header. This tag contains information about the VLAN, such as the VLAN ID and priority. The VLAN tag is inserted between the data link layer (Layer 2) and the network layer (Layer 3) headers of the packet. The diagram of packet header with VLAN tag, payload etc, would look like this:
It’s worth noting that fragmentation can cause a reduction in network performance due to the additional overhead involved in creating and transmitting the smaller packets. It’s also worth noting that some network devices, such as some routers and firewalls, may not support fragmentation and may drop packets that are too large to be transmitted.
Conclusion
In conclusion, MTU and Jumbo frame are important concepts when it comes to network performance, and understanding their impact on the network, secure traffic and other aspects of the network is important to ensure that the network is properly configured and optimized for the best performance.
