MSS clamping related query

What is MSS clamping? How it works?
Can we implement it on L2 interface or only on L3?
When we should implement it?

Let’s say you have a network setup where the Maximum Transmission Unit (MTU) of a particular link is set to 1400 bytes.

However, the default Maximum Segment Size (MSS) value set by the operating systems like windows on the connected devices is 1500 bytes.

In this scenario, if MSS Clamping is not implemented, the devices would attempt to send TCP segments of 1500 bytes over the link. Since the MTU is smaller than the MSS, fragmentation would occur. This means that the TCP segments would be broken down into smaller fragments before transmission, and the receiver would need to reassemble them, which can impact network performance and efficiency.

To avoid fragmentation and optimize the transmission, MSS Clamping can be applied. It would limit the MSS value to match the MTU of the link, in this case, 1400

By clamping the MSS, the devices will now send TCP segments of 1400 bytes or less, ensuring they fit within the constraints of the network link’s MTU. This helps prevent fragmentation and allows for smoother and more efficient data transmission between the devices.

Config t
Int fa0/1
Ip tcp adjust-mss 1400

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hi sir,

consider i have topology like machine A and machine B.

My interface is set to 1500 bytes but my connecting(machine B) is at MSS 1420bytes. How to sense the other(machine B) end MSS. Whether it is in 1420 or 1500?