Installation and Configur ation 95
Default MTUs for framing protocols are:
• Frame Relay: 4352 bytes
• HDLC: 4352 bytes
• Point-to-Point Protocol: 1496 bytes

MTU discovery facility

MTU sizes are generally selected at the host end of the route. This is
accomplished by turning on the host’s MTU discovery facility and allowing
the host to send packets. The MTU discovery facility operates by default
on the SP Switch Router. AIX4.3.1 provides MTU discovery; however, you
have to enable it with the /etc/no command.
In effect, the discovery facility tells the router not to fragment, but instead
to advise the host when the packet size is larger than the given path can
handle. This allows the host to discover the largest packet that the most
restrictive of the media components within the same path can handle.
Once "discovered", the host then sends only packets in sizes matching the
reported maximum, and so packets are not fragmented.
3.10.3 Putting grifconfig.conf Additions into Effect
Additions made to /etc/grifconfig.conf after first-time installation take effect
only after the file is reloaded and the media card reset.
Use the grreset command to reset each configured SP Switch Router
Adapter card by specifying the slot number where each card is installed, as
follows:
grreset <card_slot_number>
3.11 Step 3. Change Profile Settings
As mentioned, this step is optional and explained in detail in

GRF 400/1600

Configuration Guide 1.4,

GA22-7366. The SP Switch Router will work happily
with the default settings shipped with the system and there really is no need
to change anything at this time.
3.12 Step 4. Run dev1config
If you followed the advice in Section 3.10.1, “Method 1: Use SP SNMP
Manager - Recommended” on page 89, running the command dev1config
should be all that needs to be done.