User's Manual

Table Of Contents
416
Users Manual of CS-6306R
Run… To
ip unreachables
Enable the function to send an
ICMP-unreachable message.
2. Sending ICMP redirection message
Sometimes the host selects an unfavorable route. After a routing switch on the route receives a message from
the host, it is to check the routing table and then forward the message through the message-receiving
interface to another routing switch that is in the same network segment as the host. In this case, the routing
switch notifies the source host of directly sending the message with the destination to another routing switch
without winding itself. The redirection message requires the source host to discard the original route and take
more direct route suggested in the message. Many host’s operating system adds a host route to its routing
table. However, the routing switch is more willing to trust information obtained through the routing protocol.
Therefore, the routing switch would not add the host route according to the information.
The function is enabled by default. If the hot standby routing switch protocol is configured on the interface, the
function is automatically disabled. However, the function will not be automatically enabled even if the hot
standby routing switch protocol is cancelled.
To enable the function, run the following command in interface configuration mode:
Run… To
ip redirects
Permit sending the ICMP redirection
messafge.
3. Sending ICMP mask response message
Sometimes the host must know the network mask. To get the information, the host can send the ICMP mask
request message. If the routing switch can confirm the mask of the host, it will respond with the ICMP mask
response message. By default, the routing switch can send the ICMP mask response message.
To send the ICMP mask request message, run the following command in interface configuration mode:
Run… To
ip mask-reply Send the ICMP mask response
message.
4. Supporting route MTU detection
The system supports the IP route MTU detection mechanism defined by RFC 1191. The IP route MTU
detection mechanism enables the host to dynamically find and adjust to the maximum transmission unit (MTU)
of different routes. Sometimes the routing switch detects that the received IP message length is larger than
the MTU set on the message forwarding interface. The IP message needs to be segmented, but the
“unsegmented” bit of the IP message is reset. The message, therefore, cannot be segmented. The message
has to be dropped. In this case, the routing switch sends the ICMP message to notify the source host of the
reason of failed forwarding, and the MTU on the forwarding interface. The source host then reduces the
length of the message sent to the destination to adjust to the minimum MTU of the route.
If a link in the route is disconnected, the message is to take other routes. Its minimum MTU may be different