R1 R2 R3 each have a isp link to internet ，and each have a default-route to internet，and config the src-nat for all lan ip to internet
R1 R2 R3 together is a Independent part ，the LAN-Network just for R1 R2 R3 connect-use
R1 - R3 and R2 - R3 each have a pptp-vpn tunnel
R1 R2 R3 config the ospf-ipv4 , make PC 1234 in a local-network
question：
when i config the PC1 and PC3 access internet through R3，a bug be found
when PC1 PC3 use explorer（IE）access the internet web site，PC1 is Normal ，but PC2 is abnormal
in PC2 some web site cant be opened，but some site is very very very normal and very fast
i tried to set the mtu mru mss for fix but failed still some web site cant be opened，but some site is very very very normal and very fast
so ， if anybody take this bug ？ share the solution thank you