if someone use router, try turnoff IGMP option, restart router, turnon IGMP option (needed), maybe is router bug, but is known problem "MTU black hole" when in network path someone turn off IGMP and packets are lost, this is why some sites open, some not
if someone use router, try turnoff IGMP option, restart router, turnon IGMP option (needed), maybe is router bug, but is known problem "MTU black hole" when in network path someone turn off IGMP and packets are lost, this is why some sites open, some not