cURL to the VIP, can we do that?

It sounds like you were sniffing traffic on the BigIP. Did you try sniffing traffic on the server? Does the traffic look any different.

 

Is there anything showing up in /var/log/ltm on the BigIP?

 

Try using an irule to log the request headers and compare the curl requests and requests coming through the browser.

 

 

Finally, I would try making the request from the DOS-based device using telnet (assuming it's available to you) and do all the same testing.

 

 

I test VIPs using wget/curl and telnet/netcat and haven't run into any issues like you are describing.

 

 

HTH

 

 

Richard