User`s guide

Remarks
If DHCP is enabled (see SYSTem:COMMunicate:LAN:DHCP command), the
specified Subnet Mask is not used. However, if the DHCP server fails to
assign a valid IP address, the currently configured Subnet Mask will be
used.
Dot-notation addresses ("nnn.nnn.nnn.nnn" where "nnn" is a byte value)
must be expressed with care, as most web software on the PC will interpret
byte values with leading zeros as octal numbers. For example,
"255.255.020.011" is actually equivalent to decimal "255.255.16.9" not
"255.255.20.11" because ".020" is interpreted as "16" expressed in octal,
and ".011" as "9". To avoid confusion, use only decimal expressions of byte
values (0 to 255), with no leading zeros.
For example, the 34410A/11A/L4411A assumes that all dot-notation
addresses are expressed as decimal byte values and strips all leading zeros
from these byte values. Thus, attempting to set a Subnet Mask of
"255.255.020.011" will become "255.255.20.11" (a purely decimal
expression). Be sure to enter the exact expression, "255.255.20.11", in
your PC web software to address the instrument. Do not use
"255.255.020.011" – the PC will interpret this address differently due to
the leading zeros.
A value of "0.0.0.0" or "255.255.255.255" indicates that subnetting is not
being used.
The Subnet Mask is stored in non-volatile memory, and does not change
when power has been off, after a Factory Reset (*RST command), or after
an Instrument Preset (SYSTem:PRESet command).