Questions about setting up a VPN in OVZ

For more information about how to set up a VPN in OVZ-Linux general technology-Linux technology and application, see the following. I bought a new server and was about to build a firewall. when setting up a VPN, I encountered the following problem: VPN can be used to log on, but I cannot read Internet data through VPN, query/var/log/messages and find an error message like Cannot determine ethernet address for proxy ARP.
Netstat-r indicates that the IP address of the device is correctly allocated, but the network adapter is ppp0, and other network adapters are venet0, iptable-related content is iptables-t nat-a postrouting-s 192.168.5.0/24-o venet0-j SNAT -- to-source (external IP address of the local machine)
Iptables-t nat-a postrouting-s 192.168.5.0/24-o venet0-j MASQUERADE.
After querying the error message, the result is that the mac address of the NIC used by the ip address needs to be specified using the arp command, however, my venet0 Nic does not have a mac (if ifconfig shows that HWaddr is a full 0 address), try to modify the mac and use/sbin/ifconfig venet0 hw ether 00: 01: 02: AB: CD: if the EF command is modified, the error message SIOCSIFHWADDR: Operation not supported is returned.

Help = _ = has been stuck here