In a large network, network devices can support a variety of packet sizes that are transmitted across their interfaces. The largest packet (including headers) can be as large as the Maximum Transmission Unit (MTU). An MTU specifies the largest packet size, measured in octets, that can be transmitted through a network entity. It is important to understand the MTU of the entire path (end-to-end) when provisioning services, especially for VLL services where the service must support the ability to transmit the extra large customer packets.
The Path MTU Discovery tool is a powerful tool that enables service providers to get the exact MTU supported between the service ingress and service termination points, accurate to 1 byte.
The sdp-mtu command probes the far-end port using the configured MTU of the near-end port, not the configured MTU of the far-end port. For example, a far-end port that is physically capable of receiving jumbo frames would respond to sdp-mtu probes up to the jumbo frame size, regardless of the configured MTU of the far-end port. This assumes that the intermediate transport network can switch frames of this size.