Auto-bypassing a parent when parent is down

I have the following setup:

Computer A is running a generic/non-squid proxy server.
Computer B is running Squid.

I want computer B to use computer A as a parent for ALL requests unless
computer A is down for some reason/not-accepting requests/etc in wich
case computer B can fetch pages directly from the source.

I know how to configure squid to do this, but I can't get squid on
computer B to automatically switch back to fetching pages exclusively
through A in the event that A comes back up.

Anyone know how to do this? I've messed with the squid config file for
hours trying to acomplish this.

______________________________________________________________________________
 Matthew J. Probst | Never underestimate the bandwidth of a station
 Sys. Programmer, BYU CS Dept |wagon full of tapes hurtling down the highway.
 mprobst@cs.byu.edu | -Andrew Tanenbaum
Received on Thu May 21 1998 - 15:50:40 MDT