pppd errors bring down NFS?

[Marty <martyb@ix.netcom.com>]

I'm getting intermittent errors on my DSL connection, which
I think is a telephone line issue that I've seen before.

It seems that each time my connection drops, I lose my NFS
connections.  In /var/log/messages I find many repetitions of:

  kernel: RPC: sendmsg returned error 1
  kernel: nfs: RPC call returned error 1

Once my PPP connection is re-established, NFS comes back.  Other
LAN traffic seems inaffected, or at least not for as long a
period.  From watching ps output it seems ipdown/ipup may be
getting called, which could explain the disrupted NFS
connection.  Is this Debian or some anomaly in my system?
How do I find out?  Thanks for any ideas and suggestions.