I have a Juniper Networks Netscreen firewall connected to an ADSL bonding device (xrio UBM 400). The firewall has a static IP address (as does the bonder) but the firewall keeps disappearing and becomes completely unaccessible - PING fails and so on. This happens unpredictably but regularly when the Internet connection is being used.
The bonder manufacturer says that the bonder sends out an ARP request to the firewall immediately prior to it disappearing and that no response is returned. They are replacing the firewall with a Cisco unit but I'm interested/concerned to know what the problem here might be - why would the firewall do this? It seems to remain accessible perfectly well by the static IP address when the internet connection isn't being used.