Hi Rene,
I tried this on WAN interface because my ISP uses DHCP, but didn’t make any difference to client-id.
interface GigabitEthernet0/1
ip address dhcp client-id GigabitEthernet0/1
ip access-group INTERNET in
ip nat outside
ip inspect FIREWALL out
ip virtual-reassembly in
Aug 13 23:42:47 UTC: Retry count: 1 Client-ID: cisco-c471.fec5.39d9-Gi0/1
Aug 13 23:42:47 UTC: Client-ID hex dump: 636973636F2D633437312E666563352E
Aug 13 23:42:47 UTC: 333964392D4769302F31
Aug 13 23:42:47 UTC: Hostname: c2901
Aug 13 23:42:47 UTC: DHCP: SRequest - ciaddr: x.x.x.x
Aug 13 23:42:47 UTC: DHCP: SRequest placed class-id option: 636973636F706E70
Aug 13 23:42:47 UTC: DHCP: SRequest: 304 bytes
Aug 13 23:42:47 UTC: DHCP: SRequest: 304 bytes
Aug 13 23:42:47 UTC: DHCP: Received a BOOTREP pkt
Aug 13 23:42:47 UTC: DHCP: Scan: Message type: DHCP Ack
Aug 13 23:42:47 UTC: DHCP: Scan: Client ID: cisco-c471.fec5.39d9-Gi0/1