Cisco Systems OL-8241-02 Manual De Usuario

By default, the CSS establishes an implicit (or internal) service for the gateway 
address when a static route is defined. When you do not want the CSS to start an 
implicit service for the next hop of a static route, use the ip no-implicit-service 
command. The ip no-implicit-service command specifies that no implicit service 
is established to the next hop of the static route, which disables the internal 
service ICMP keepalive. In this case, if the ARP address for the next hop is not 
known to the CSS, the address will not appear in the routing table.

The purpose of the implicit service to the next hop of a static route is to monitor 
the availability of the next hop to forward data traffic. When the ip 
no-implicit-service command is in effect, traffic is forwarded to the next hop 
even when the next hop is unavailable. Because of the possibility of data being 
lost if the next hop becomes unavailable, use of the ip no-implicit-service 
command is strongly discouraged. 

Static routes can sometimes appear in the CSS routing table even when you have 
an implicit service for the next hop address (the default setting) and the internal 
keepalive is down. When the CSS detects the ARP mapping for the next hop in the 
static route, the CSS continues to list that route in the routing table regardless of the 
state of the ICMP service keepalive (Down or Up). 

When you implement the ip no-implicit-service global configuration command, 
this action does not affect previously configured static routes. The ip 
no-implicit-service command affects only those static routes added after you 
enable the command. We recommend you reboot the CSS after you modify the 
configuration to ensure all static routes are the same, which is useful for network 
monitoring and troubleshooting. If you wish to stop the implicit service for a 
previously configured static route, then you must delete and reconfigure the static 
route.