Cisco Recommends Dual NIC deployment for Expressways. But single NIC deployment can be achieved.
Points to be noted for single NIC:
> Firewall must support NAT Reflection, if not then you can use dual NATing to achieve NAT reflection on unsupported firewall like Fortigate.
> If you're geolocation doesn't support PSTN calls over internet then you need to block them through Device Mobility.
> Need to resolve SRV's.
The DNS configuration should be:
externaldomain.com on the external:
resolving only the Expressway-E.
externaldomain.com on the Internal:
Resolving only the CUCM & IM&P servers.
If you still have more queries feel free to comment.
