Why does tc-netem on loopback also affects other interfaces?

I'm trying to modify the network behaviour of my server(s), to simulate *external/WAN connection behaviours* (what ever that means). After doing tc qdisc add dev lo root netem delay 100ms, I can successfully add 100ms delay to all traffic from (and to?) 127.0.0.1. E.g. ping 127.0.0.1 will have 200ms response time. However, this also affect my traffic to other interfaces. For example, I have interface eth1 with IP address 192.168.0.1 on the current server A. If I do ping 192.168.0.1, it will also have the 100ms delay (resulting in 200ms response time). I'm confused by this behaviour. I would expect lo has nothing to do with eth1, but it seems not to be the case. I assume this means Linux kernel automatically identifies 192.168.0.1 is a local address, and re-routes all traffic (originally to eth1) to lo? And if so, is there a way to **disable** this behaviour? ---- Background: I would like to simulate *external network* behaviour even when processes on server A want to communicate to each other (through TCP/IP on the given local addresses and ports, of course). Essentially I want to add delay to eth1, but that's above this question (see my other question ). My servers are running Ubuntu 18.04, but I believe that does not matter.