In the case that the MTU is less than 1500 bytes, the bandwidth will increase, all this is taken based on the control information of the various protocols, specifically the header.

On the other hand, if the MTU is greater than 1500 bytes, the bandwidth taken in the headers will decrease and the maximum possible payload will be sent in each packet. However, if an intermediate node through which the packet passes cannot handle such large packets, packet fragmentation and reassembly will be performed, which also decreases the efficiency of the connection.

Having an MTU (Maximum Transmission Unit) set to a value less than 1500 bytes on a network can cause browsing or connectivity problems with some web pages or online services. Here I explain why this happens and what you can do about it.

Why might an MTU less than 1500 bytes cause problems?

The MTU represents the maximum size of data packets that can be transmitted on a network. The standard for Ethernet is an MTU of 1500 bytes, and many networks are configured with this value by default. When a data packet exceeds the configured MTU size, it must be fragmented into multiple smaller packets for transmission, which can lead to several problems:

1. Fragmentation: Packet fragmentation increases the load on network devices and can reduce the efficiency of data transmission. Additionally, some end systems or intermediate devices may not correctly handle the reassembly of fragmented packets.
2. Packet Loss: If fragmentation occurs and a segment is lost, the entire original packet must be retransmitted, which can lead to reduced performance and slower speeds.
3. Problems with Protocols and Applications: Some applications and protocols are sensitive to fragmentation and may not function correctly when packets are fragmented. This is particularly true for security protocols such as IPsec, which may require a lower MTU to accommodate additional headers without fragmenting packets.
4. Timeouts and Connection Errors: Excessive fragmentation and packet handling issues can cause connection timeouts and errors, which can manifest as problems loading web pages or performing certain online actions.

Solutions

If clients on your network are experiencing browsing issues and you suspect the MTU may be the culprit, here are some actions you can take:

1. MTU Path Discovery: Make sure MTU Path Discovery is enabled on your devices. This allows the network to automatically determine the best MTU along the path between the host and server, minimizing fragmentation problems.
2. MTU Value Setting: Consider adjusting the MTU value on your network devices. In some cases, setting a slightly lower MTU (for example, 1492 bytes, common on PPPoE connections) on the client side can help, but it is important that this setting be made with knowledge of the implications and tested appropriately.
3. Review VPN Settings: If problems occur over VPN connections, check the MTU settings on the VPN. VPNs often require a lower MTU due to encapsulation overhead, and adjusting this value can resolve connectivity issues.
4. Communication with the ISP: If local settings do not resolve the issue, it may be helpful to contact your ISP. The MTU issue may be occurring outside of your local network, and the ISP may need to make adjustments.

In conclusion, while an MTU less than 1500 bytes may be necessary in certain circumstances, it is important to understand and carefully manage its effects to ensure an optimal browsing and connectivity experience.