Diagnostic tools are critically important. It’s something that often gets forgotten in product development, but it can make or break a product, especially in a product’s formative years (or during big code updates) while the kinks are being worked out.
The swiss army knife of diagnostic tools, and the one most essential in the entire networking realm, is tcpdump. Most load balancers these days have this installed, from the big-budget F5 BIG-IP to the value boxes, tcpdump is included.
It’s one of the benefits of the proliferation of x86-based load balancers, and an advantage they have over some of their switch/ASIC-based counterparts. While it’s possible for the switch-based system to just set up a mirror/span port and use a sniffer (or Linux box with tcpdump installed), it’s far more convenient when tcpdump is installed on the device itself.
