User's Manual

Table Of Contents
417
Users Manual of CS-6306R
from the original route. The routing switch then notifies the source host of the MTU of the new route. The IP
message should be packaged with the minimum MTU of the route as much as possible. In this way, the
segmentation is avoided and fewer messagesare sent, improving the communication efficiency.
Relevant hosts must support the IP route MTU detection. They then can adjust the length of IP message
according to the MTU value notified by the routing switch, preventing segmentation during the forwarding
process.
5. Setting IP maximum transmission unit
All interfaces have a default IP maximum transmission unit (MTU), that is, the transmissible maximum IP
message length. If the IP message length exceeds MTU, the routing switch segments the message.
Changing the MTU value of the interface is to affect the IP MTU value. If IP MTU equals to MTU, IP MTU will
automatically adjust itself to be the same as new MTU as MTU changes. The change of IP MTU, however,
does not affect MTU. IP MTU cannot bigger than MTU configured on the current interface. Only when all
devices connecting the same physical media must have the same MTU protocol can normal communication
be created.
To set IP MTU on special interface, run the following command in interface configuration mode:
Run… To
ip mtubytes
Set IP MTU of the interface.
6. Authorizing IP source route
The routing switch checks the IP header of every message. The routing switch supports the IP header options
defined by RFC 791: strict source route, relax source route, record route and time stamp. If the switch detects
that an option is incorrectly selected, it will send message about the ICMP parameter problem to the source
host and drop the message. If problems occur in the source route, the routing switch will send ICMP
unreachable message (source route fails) to the source host.
IP permits the source host to specify the route of the IP network for the message. The specified route is called
as the source route. You can specify it by selecting the source route in the IP header option. The routing
switch has to forward the IP message according to the option, or drop the message according to security
requirements. The routing switch then sends ICMP unreachable message to the source host. The routing
switch supports the source route by default.
If the IP source route is disabled, run the following command in global configuration mode to authorize the IP
source route:
Run… To
ip source-route Authorizing IP source route.