Check Network and TCP/IP Performance¶

Measure SCP throughput without writing to disk.
```
$ SCP 192.168.20.131:"test/linux.bck" NL:

linux.bck               |   60MB | 7716.7 kB/s | TOC: 00:00:08 | 100%
```
Uses a null device (NL) as the destination rather than a disk, allowing network/TCP/IP throughput to be measured independently of disk performance.
Compare performance with FTP.
If OpenVMS is the FTP serverIf OpenVMS is the FTP client
FTP> PUT [filename] NL:
FTP> GET [filename] NL:
If these tests are significantly faster than disk writes, the bottleneck is unlikely to be the network/TCP/IP layer. Proceed to SCP and SFTP Tuning.
Check for duplex mismatches.
```
$ MCR LANCP SHOW DEVICE/INTERNAL_COUNTERS
```
If "possible duplex mismatch" is reported, adjust the NIC duplex settings.
Disable PMTU.

Caution

Changing the PMTU setting affects all TCP/IP traffic and may cause connection loss. Use only as a last resort.
```
TCPIP> SYSCONFIG -R INET PMTU_ENABLED=0
```
PMTU affects WAN performance only.
Increase TCP send and receive buffers.

Caution

SB_MAX setting affects all of TCPIP and may result in increased memory load on a system. TCP_SENDSPACE and TCP_RECVSPACE setting affects all TCP connections and may result in increased memory load on a system. Use only as a last resort.

Check current values:
```
TCPIP> SYSCONFIG -Q SOCKET

TCPIP> SYSCONFIG -Q INET TCP_SENDSPACE TCP_RECVSPACE
```
Increase the buffer sizes:
```
TCPIP> SYSCONFIG -R INET TCP_SENDSPACE=1000000 TCP_RECVSPACE=1000000
```
If OpenSSH is the SCP/SFTP server, restart SSH:
```
$ @SYS$MANAGER:TCPIP$SSH_SHUTDOWN.COM
$ @SYS$MANAGER:TCPIP$SSH_STARTUP.COM
```
If OpenVMS is the FTP client, start a new FTP session.