Dances with macs?

Question

Cisco

The following situation has arisen.
We have such a vile provider that binds to the MAC of the terminal equipment (greet Comstar / MTS). It was required to poke his link into Tsiska (ISR). And that source device in DMZ (which looks in a tighter tsiska). On Gi0 / 0, the mac of the previous router was registered and everything successfully crowed. And the first router was stuck in the DMZ. So he doesn't want to be friends with Tsiska. Naturally, on the DMZ interface, the MAC is native. Yes, and he (the old router) goes to the Internet through a different channel (although this is no longer important).
In theory, everything should work so quietly, because. Gi0/0 and DMZ do not intersect at the L2 level. However, damn it, it doesn't work. Where to dig to "isolate" interfaces at the L2 level?
PS I really would not want this to be a "feature" of the platform.
PPS Changing the MAC of the first router is not an option, it does not know how to do this.

Answer 1

DMZ is what interface? The case is not a sub gi0 / 0? What does sh int say on it? What will happen if you change the poppy on it? What exactly doesn't work? What does sharp say?