ASR9k and 7600 (when using EVC configuration) are so-called EFP platforms. This means that dot1q tag is not stripped off by default, but you have to use ‘rewrite’ commands like: “rewrite ingress tag pop 1 symmetric” In case of Type 4 pseudowire (Ethernet VLAN), if you strip off the tag with rewrite you’ll be left without any tags. To facilitate this we add so-called ‘dummy tag‘. ‘transport-mode vlan passthrough‘ is special version of Type 4 PW, which doesn’t insert dummy tag. So, in this case in order to keep original dot1q tag, we should not use ‘rewrite’ command.