User's Manual

395
Command Purpose
ip mtu bytes
Sets 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. 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:
Command Purpose
ip source-route
Authorizes IP source route.
(7) Allowing IP Fast Exchange
IP fast exchange uses the route cache to forward the IP message. Before the SWITCH forwards message to
a certain destination, its system will check the routing table and then forward the message according to a route.
The selected route will be stored in the routing cache of the system software. If latter message will be sent to
the same host, the SWITCH will forward latter message according to the route stored in the routing cache.
Each time message is forwarded, the value of hit times of the corresponding route item is increasing by 1.
When the hit times is equal to the set value, the software routing cache will be stored in the hardware routing
cache. The following message to the same host will be forwarded directly by the hardware. If the cache is not
used for a period of time, it will be deleted. If the software/hardware cache items reach the upper limitation,
new destination hosts are not stored in the cache any more. This SWITCH series can hold 2074 hardware
cache items and 1024 software cache items.
To configure the hit times required when the software cache items are stored to the hardware cache, run the
following command in global configuration.
Command Purpose
ip route-cache hit-numbers hitnumber
When the hit times of the routing item in the software
cache reaches the value of the parameter hitnumber, the
routing item in the software cache will be stored as a