Imao sam isti problem i rešio sam tako što sam podesio MTU na 1500. Ako posle njega iamš neki ruter i na njemu treba da su iste vrednosti.

Povecao sam ali nece opet

iz manuala:

Change MSS
It is a well known fact that VPN links have smaller packet size due to
incapsulation overhead. A large packet with MSS that exceeds the MSS of the
VPN link should be fragmented prior to sending it via that kind of
connection. However, if the packet has DF flag set, it cannot be fragmented
and should be discarded. On links that have broken path MTU discovery
(PMTUD) it may lead to a number of problems, including problems with FTP and
HTTP data transfer and e-mail services.
In case of link with broken PMTUD, a decrease of the MSS of the packets
coming through the VPN link solves the problem. The following example
demonstrates how to decrease the MSS value via mangle:

[admin@MikroTik] > /ip firewall mangle add out-interface=pppoe-out \
\... protocol=tcp tcp-flags=syn action=change-mss new-mss=1300 chain=forward
[admin@MikroTik] > /ip firewall mangle print
Flags: X - disabled, I - invalid, D - dynamic
0 chain=forward out-interface=pppoe-out protocol=tcp tcp-flags=syn
action=change-mss new-mss=1300


Ja sam stavio na 1300 i radi mi:))

Promenio sam i ništa
Sve je isto kao pre, sve ide samo ne ide msn i icq

Da ti nisu blokirani neki portovi?

Da bilo je mss-a upravu je mika_vk, nesto sam pogresio pa sam to ispravio i sada je to ok.