What additional issue arises when using Q-in-Q tunneling related to MTU?

When using Q-in-Q tunneling, a significant issue related to Maximum Transmission Unit (MTU) is that the MTU for tunneled frames exceeds the default limit. Q-in-Q, or VLAN stacking, encapsulates a customer's original VLAN frame within an additional VLAN tag. This encapsulation effectively adds extra bytes to each frame, leading to an increase in the frame size.

Standard Ethernet frames have a default MTU size of 1500 bytes. When you add an additional tag through Q-in-Q, the size of the frame can increase up to 1522 bytes, which surpasses the default MTU. If network devices do not properly handle frames that exceed the standard MTU size, they may drop the encapsulated packets, causing connectivity issues and fragmenting the traffic.

Adjusting MTU settings on network devices is essential when implementing Q-in-Q to ensure that the encapsulated traffic can be transmitted without issues. By configuring devices to accommodate the larger MTU, you can prevent packet loss and maintain the integrity of the data being transmitted across the network. Thus, understanding the implications of MTU in relation to Q-in-Q tunneling is critical for effective network performance and reliability.