MTU here. MTU there too?

[senser]

DSL (over PPPoE) home user here.
So my WAN interface (pppoe0) uses an MTU of 1492. To avoid fragmentation - should I set my LAN and OPT interfaces MTU to 1492 too - or is it enough to set that MTU on the client computers that connect at LAN/OPT?
Links that nicely describe the whole MTU MSS issue will work too! Thx :)

PS: I wish my DSL provider would just use DHCP auth… I just called the support of my DSL provider here in germany and asked about the possibility of using DHCP instead of PPPoE and since he never even heard about the possibility he always tried to taught me about the real use of DHCP and said that I am confusing things...he even laughed at me in the end. :(

[cmb]

On WAN alone is adequate, we enable MSS clamping to prevent TCP from being bigger than that.