An interesting question. In terms of ICMP you could alway ping between hosts behind your routers for manual testing. However for automated testing then ip sla would be the way to go. Also some traffic types are more tolerant of loss than others. For example TCP traffic e.g. HTTP can recover from lost segments whereas UDP cannot (unless this is done at an upper layer of course like in TFTP or SIP). UDP is used extensively for real time traffic like voice vans video, so those applications would become unusable if there is high packet loss, delay, or jitter (variance in delay).
Ip sla allow you setup monitors for different types of traffic as required, which can then tracked and thus generate management information.
Tools like this form the basis for Pfr (formerly OER) but this is probably out of scope for this post.
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