探测目的地址是否存活，多用于多链路出口探测使用。可用于关联路由、策略路由、防火墙双机切换等。实现高可用性，各个厂商都有相关技术，以下举例思科、华为、Juniper配置方法。

思科

ip sla 2 //SLA 编号
icmp-echo 192.169.9.66 source 192.168.1.2 //探测目的地址并指定源地址
timeout 10000 //超时时间10000毫秒
frequency 20 //探测频率20秒一次
ip sla schedule 2 life forever start-time now //sla探测策略为永久，开始时间为现在
track 2 ip sla 2 reachability //track与sla 关联
ip route 192.192.9.0 255.255.255.0 192.168.1.1 track 2 //关联路由

华为：ip-link
ip-link check enable // 全局使能ip-link 功能
ip-link 1 destination x.x.x.z timer 5 mode icmp //ip-link 编号、超时时间、模式（除ICMP外还有arp模式）
ip route-static 0.0.0.0 0.0.0.0 x.x.x.z preference 50 ip-link 1 //关联IP-link

Juniper： ip monitor

RPM Configuration
set services rpm probe Probe-Server test testsvr target address 1.1.1.1 >> RPM Probes test for the target in first ISP.
set services rpm probe Probe-Server test testsvr probe-count 10
set services rpm probe Probe-Server test testsvr probe-interval 5
set services rpm probe Probe-Server test testsvr test-interval 10
set services rpm probe Probe-Server test testsvr thresholds successive-loss 10
set services rpm probe Probe-Server test testsvr thresholds total-loss 5
set services rpm probe Probe-Server test testsvr destination-interface ge-0/0/0.0
set services rpm probe Probe-Server test testsvr next-hop 1.1.1.1

set services rpm probe Probe-Server1 test testsvr target address 2.2.2.2 >> RPM Probes test for the target in second ISP.
set services rpm probe Probe-Server1 test testsvr probe-count 10
set services rpm probe Probe-Server1 test testsvr probe-interval 5
set services rpm probe Probe-Server1 test testsvr test-interval 10
set services rpm probe Probe-Server1 test testsvr thresholds successive-loss 10
set services rpm probe Probe-Server1 test testsvr thresholds total-loss 5
set services rpm probe Probe-Server1 test testsvr destination-interface ge-0/0/1.0
set services rpm probe Probe-Server1 test testsvr next-hop 2.2.2.2
IP-Monitoring Configuration
set services ip-monitoring policy Server-Tracking match rpm-probe Probe-Server
set services ip-monitoring policy Server-Tracking then preferred-route routing-instances FBF-1 route 0.0.0.0/0 next-hop 2.2.2.2 >> Installs route in the first routing-instance

set services ip-monitoring policy Server-Tracking1 match rpm-probe Probe-Server1
set services ip-monitoring policy Server-Tracking1 then preferred-route routing-instances FBF-2 route 0.0.0.0/0 next-hop 1.1.1.1 >> Installs route in the second routing-instance