iOS TLS/SSL Handshake Adding Overhead to F5 VPN Connections

Number:rdar://452145415 Date Originated:6.20.2017
Status:open Resolved:no
Product:iOS Product Version:10.3.2 (14F89)
Classification:Network Reproducible:Always
I am seeing increased overhead in TLS handshakes from the iPad device to the server over VPN.  The device VPN we are using is F5 and our application is distributed through a mobile device management system (AirWatch). The iPad application has a lot of networking activity running under the hood and the current server configuration requires the application to make a SSL handshake on every network request going through the F5 VPN to the server.  Many the TLS/SSL handshakes that are made between the device and the server happen within the 100-250ms range.  However, there are many that take between 400-600ms also to complete.  My concern is that with the large amount of networking requests that are made, and with a TLS handshake on every request, is there anything that can be done to reduce the overhead in the TLS/SSL handshake? 

Device Configuration:
1. Cellular connected iPad Air 2 (iOS 10.3.2) with AirWatch (MDM).
2. Connect on Demand with F5 BIG-IP VPN.

1. Upon opening the application observe 100+ network connections being run through the VPN in the background.
2. From the device logs observe variable TLS/SSL handshake times ranging anywhere from 100ms to 600ms.

10.3.2  (14F89)

WiFi connections observe similar TLS overhead but not as significant.


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