Hi all,

I load balance between 5 WAN lines. Pre-3.17 I just set my WAN interface MTU to 1454 as tested using TCPOptimizer.
Recently my users are experiencing problems with some sites, seemingly a MTU problem. Then I heard that I should mangle the Change-mss to MTU-40
I do not use PPTP, just plain routing & NAT
A)Is it needed to change the MSS with a mangle rule?
B)Must I also use MSS=MTU-40 or can it be less (without PPTP)
C)Where do I do this, below is the existing rules for my 5 WAN lines.
Must I add a seperate mangle rule in between each connection-mark/routing mark below or can 1 'global' rule do it?

add action=mark-connection chain=prerouting comment=CM1 connection-state=new \
disabled=no in-interface=TRUE new-connection-mark=Cone nth=5,1 \
passthrough=yes
add action=mark-routing chain=prerouting comment=RM1 connection-mark=Cone \
disabled=no in-interface=TRUE new-routing-mark=Rone passthrough=no


add action=mark-connection chain=prerouting comment=CM2 connection-state=new \
disabled=no in-interface=TRUE new-connection-mark=Ctwo nth=4,1 \
passthrough=yes
add action=mark-routing chain=prerouting comment=RM2 connection-mark=Ctwo \
disabled=no in-interface=TRUE new-routing-mark=Rtwo passthrough=no


add action=mark-connection chain=prerouting comment=CM3 connection-state=new \
disabled=no in-interface=TRUE new-connection-mark=Cthree nth=3,1 \
passthrough=yes
add action=mark-routing chain=prerouting comment=RM3 connection-mark=Cthree \
disabled=no in-interface=TRUE new-routing-mark=Rthree passthrough=no


add action=mark-connection chain=prerouting comment=CM4 connection-state=new \
disabled=no in-interface=TRUE new-connection-mark=Cfour nth=2,1 \
passthrough=yes
add action=mark-routing chain=prerouting comment=RM4 connection-mark=Cfour \
disabled=no in-interface=TRUE new-routing-mark=RFour passthrough=no


add action=mark-connection chain=prerouting comment=CM5 connection-state=new \
disabled=no in-interface=TRUE new-connection-mark=CFive passthrough=yes
add action=mark-routing chain=prerouting comment=RM5 connection-mark=CFive \
disabled=no in-interface=TRUE new-routing-mark=RFive passthrough=no

You can try this to force mss to 1440 for example:
Also ensure that you dont have a conflicting rule popping up as a result of an "change tcp mss = yes" in the profile for the connection (PPP|Profiles inside winbox)