NetEng here, I'm usually troubleshooting lower layer issues (Ethernet, MPLS, IP) than HTTP however, tcpdump is one of my go-to tools every time.

If anyone is interested I've made some notes here: https://null.53bits.co.uk/index.php?page=tcpdump-notes

For example, imagine spanning/mirroring a 10G backbone link, how many people are pinging 8.8.8.8 all the time. I can ping with a specific DSCP value set to isolate my pings from anyone elses, looking into the reported issue of 8.8.8.8 latency, then apply a filter to tcpdump on my mirrored port that matches ICMP traffic to a specific IP, with a specific DSCP value, inside specific L3 VPN (specific MPLS labels) etc.

sudo tcpdump -nlASX -s 65535 -vvv -i eth3 '(mpls 52634 and (ip and (ip[1] & 0xfc) >> 2 > 0x01) and host 11.22.33.44 and icmp)'

I love tcpdump's filtering capabilities.