---
title: client.socket.tcpi_snd_mss
summary: null
url: >-
  https://www.fastly.com/documentation/reference/vcl/variables/client-connection/client-socket-tcpi-snd-mss
---

**Type:** INTEGER  
**Access:** read-only

**Available in:** recv, deliver, log, error

The current maximum segment size (MSS), in
bytes, used for transmitting packets in the current TCP connection to
the client. Its initial value is the minimum of the MSS option
received from the client during connection handshake and the
historical MSS available on this path.

Changes detected in path maximum transmission unit 
(PMTU), even by other connections to the same peer, can result in the
MSS changing during the lifetime of the connection. Larger values are
more efficient as the per-packet overhead is reduced, but smaller
values transit the internet more reliably. MSS values are slightly
smaller than PMTU to allow room for TCP and IP overhead.