Slow Performance via RED15 / RED15w related to CITRIX- Sessions and RDP- Sessions - SG330 Cluster

Question

Hello, 
 we have two SG330 devices that operate in a hot-standby cluster. 
 The internet connection in our main office, where the firewall cluster are located, is 50.000 Mbit/s SDSL (Up- and Download). 
 If we use a new RED15w device on a good performing internet connection (20.000 Mbit/s) and let it connect to our main office, 
 rdp sessions to server 2012 servers are slow and laggy. 
 If we connect to our CITRIX- Farm it results in a very poor connection performance! We wait three to ten minutes, 
 until the user login process is finished. And after that its impossible to work in the CITRIX- Session (very very laggy). 
 (We see in CITRIX Director that after tge CITRIX- Login the disk latency peaks up from 40.000 to 90.000 ms - normal: 30-70 ms...) 
 The problems only occur, if we connect via RDP or CITRIX behind a RED- Box. 
 On direct Internet or SSL- VPN- Connections the problems don't occur! 
 
 Does anyone have an idea? 
 
 Thank you so far. 
 
 Best regards 
 Ben

SaschaParis · Accepted Answer

Do not lower MTU on the RED Interface or even worse the WAN interface. 
 https://support.citrix.com/article/CTX115434 
 
 Configure a appriopriate MTU directly on the Citrix Servers Interface (there was once in the past a KB from Citrix, how and where this in the registry can be done), or on the internal interface of the UTM, where the Citrix Server sits (not the preferred way, as it also affects nono Citrix traffic too) 
 
 /Sascha

SaschaParis · Answer

Hi Ben 
 
 Any news on that one ? Wonder if the hint did help ? 
 
 /Sascha