The Environment: Tuning for Performance - The Data Access - page 104

Driver

Router Router Router

MTU = 1500 MTU = ? MTU = ? MTU = ? MTU = ?

Figure 4-19 Network analysis of MTU

In the following examples, we use the ping (Windows) and traceroute
(UNIX/Linux) commands to determine if packet fragmentation occurs along
this network path for a 1500-byte packet, and we find the optimal packet size for
the network path.

Example A: Detecting Packet Fragmentation on Windows

1. At a command prompt, enter the ping command to test the connec-

tion between the client and database server. The -f flag turns on a
“do not fragment” (DF) field in the header of the packet, forcing the
ping command to fail if the packet needs to be fragmented at any
network node along the path. The -l flag sets the packet size. For
example:

ping UK-server-03 -f -l 1500

If packet fragmentation is needed, the ping command fails with the
following message, which indicates that the packet was not frag-
mented because the DF field was set:

Packet needs to be fragmented but DF set

2. Reissue the ping command repeatedly, each time lowering the size

of the packet in logical increments (for example, 1500, 1475, 1450,
1425, 1400, and so on) until a message is returned indicating that
the command was successful.