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Disappearing IP addresses

Hopefully this will help someone else.

I had a problem with my additional static IP addresses dropping. From reading a few forums I surmise this is a common problem with DSLExtreme. I first opened a ticket with support and was told "we cannot not fix it". Whether that meant DLSExtreme or their support people was unclear. Consequently, I did some experimenting and discovered that the IP addresses stopped responding after about an hour. This was consistent and repeatable indicating it is a "feature" of the DLSExtreme network. From clustering maybe? After a little more testing, I found I could bring them back by sending ARP requests to the gateway.

Since I use a Linux box as my firewall/router I solved this simply by sending an gratuitous arp periodically. I have cron run a short script that executes following command for each of my IPs:

arping -q -c 1 -I [interface] -s [local IP] [gateway IP]

After 24 hours, the IPs are still stable. As a bonus, it also seems to keep my primary IP from occasionally hanging up secure shell sessions to/from work.

If you do not have a Linux box at the edge of your network, most firewalls can be configured to do the same thing for an IP address on an interface or sub-interface. Look for "gratuitous arp" in the configuration utility.

It is the client side router/device that is responsible for renewing the lease. Clients that are configured properly should renew the lease when half the lease time is left as part of the renewal protocol.

See below from the following site. »technet.microsoft.com/en-us/libr···nSection

Renewing
IP addressing information is leased to a client, and the client is responsible for renewing the lease. By default, DHCP clients try to renew their lease when 50 percent of the lease time has expired. To renew its lease, a DHCP client sends a DHCPRequest message to the DHCP server from which it originally obtained the lease.
The DHCP server automatically renews the lease by responding with a DHCPAck message. This DHCPAck message contains the new lease as well as any DHCP option parameters. This ensures that the DHCP client can update its TCP/IP settings in case the network administrator has updated any settings on the DHCP server. Figure 4.9 illustrates the Renewing state.

Figure 4.9 The Renewing State
Once the DHCP client has renewed its lease, it returns to the Bound state. Renewal messages (DHCPRequest and DHCPAck) are sent by media access control and IP-level unicast traffic.
--
George
General Manager
DSL Extreme
Will work for reviews.

These are static IPs not DHCP.