Internet Core Protocols: The Definitive Guide

Clients Can’t Connect to Network Resources

If your DHCP clients are coming and going frequently (due to short DHCP lease timers or due to clients releasing their leases when they aren’t needed), then it is likely that you will encounter connectivity problems due to old entries in other systems’ ARP caches.

You may also encounter this problem with users who frequently connect and disconnect from multiple dial-in servers on the same Ethernet LAN, and who always use the same IP address regardless of the dial-in server that they connect to. Since these servers will provide Proxy ARP services to the remote users, it is highly likely that the ARP caches on the various network devices will get out-of-synch at some point.

One solution to this problem would be to cut back on your DHCP or dial-in lease activity. Essentially, this solution suggests that you try to minimize the hardware and IP address changes, and do your best to keep them synchronized for as long as possible.

Another option would be to seek out DHCP and dial-in servers that support UnARP or Gratuitous ARP. UnARP would cause the cache entries on the local devices to get flushed when the DHCP or dial-in addresses were released, while Gratuitous ARP would update any devices on the local network with the new hardware address associated with the dial-up system’s IP address.