The helper-address is not just relaying DHCP

• Port 37: Time
• Port 49: TACACS
• Port 53: DNS
• Port 67: DHCP/BOOTP server
• Port 68: DHCP/BOOTP client
• Port 69: TFTP
• Port 137: NetBIOS name service
• Port 138: NetBIOS datagram service

By default, the ip helper-address command forwards the following eight UDP services: