NE40 and client's GSR connect ISIS and it is unusable. Display isis peer and there is no neighbor.
1. Check ISIS configuration and it is not problematic.
2. The isis level of both sides is consistent. network-entity is correct.
3. Check interconnected POS of NE40 and C client's GSR and the MTU is 1500, but default MTU of NE40 POS is 4470. It is possible that POS MTU of opposite device is not 1500 and the MTU mismatches.
Through check client GSR POS is default value (not 1500). ISIS requires that the MTU of interconneted interface is consistent. Change MTU as 1500. ISIS neighbor relation is established and the route can be learnt.
It is possible that the mismatch of parameter configuration causes negotiation not to pass.