Where outer switch is Netgear DS524 (previously some Linksys). NSA TS and NSA HA are Sonciwall 2400 family. Internet test gateway and WiFi are network devices before a firewall (a PC and a wireless guest AP).
I have tested if there are packet loss on VLANs behind a firewall but all work as should.
What can cause those packet loss on that outer switch? Any good suggestions for a hardware replacement (up to 8 ports, rack mountable)?