No network upsets gnome

Question

An issue that has been bothering me for over a year now. My notebook, running ubuntu 10.04, is almost all the time using a wired connection, with static IP address. And a remote DNS server. Network is configured with entries in /etc/network/interfaces and /etc/resolv.conf, rather than whatever the gnome UI tool was (*)

But if I'm out, or simply unplug the network cable, a few things get weird. Specifically the gnome-panel stops working - it is still there, but isn't updating. And opening a nautilus window (e.g. to look at files on the local disk) has huge time-outs. By that I mean it will not open the window for something like 30 or 60 seconds; but when it does finally open it I can see the files and it is perfectly usable.

Everything else works fine, alt-tab between windows, etc. I use the commandline to find the pid of gnome-panel, kill it, wait a couple of seconds, and it opens up a fresh panel which is normally usable.

(Something like 10 minutes later it will have locked/crashed again; the same for the nautilus windows.)

I'm guessing this is a DNS issue? Would setting up a local DNS server help? [No, see UPDATE#2 below] Guess number 2 was related to having a file server mount (samba, though running on another linux box), and symbolic links to files and directories on that file server on my desktop.

My question is a bit vague... Does anyone recognize these symptoms, and have a suggestion? Or do you have some troubleshooting suggestions for narrowing down the problem?

I mount my samba drive with an entry in /etc/rc.local:

mount -t cifs -o "user=guest,rw,iocharset=utf8,nounix,uid=darren,gid=darren,dir_mode=0775,file_mode=0664" //10.0.1.99/xxx /mnt/xxx

(This approach has worked well for the almost-always-have-a-wired-connection setup I have.)

My /etc/hosts:

127.0.0.1   localhost
127.0.1.1   myhost

# The following lines are desirable for IPv6 capable hosts
::1     localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

127.0.0.1      testsite.local

#Other test website URLs here

UPDATE: Some timings to open some desktop folder icons. This is after pulling out the network cable. A sub-directory of the desktop took 23 secs to open up. Content appears immediately (just 8 files, it has no further subdirectories). The home directory icon took 12 seconds to open up, but then took about 30 seconds for the files to appear. I closed it and tried again. This time it took 18 seconds to open up, but then 70 seconds before anything appeared.

UPDATE #2: I tested the DNS server by installing bind9 package. It seems to come ready configured as a cache-only DNS server, so all I did was add 127.0.0.1 to the top of /etc/resolv.conf. (I also added my previous DNS server in the forwarders section of /etc/bind/named.conf.options.) It did not help. But I was tail-ing syslog, and this is what I saw when clicking the home icon on my desktop, after removing the network cable:

Jun 12 09:06:54 myhost kernel: [479308.182192]  CIFS VFS: Unexpected lookup error -112
Jun 12 09:07:04 myhost kernel: [479318.179143]  CIFS VFS: Unexpected lookup error -112
Jun 12 09:07:14 myhost kernel: [479328.186138]  CIFS VFS: Unexpected lookup error -112
Jun 12 09:07:24 myhost kernel: [479338.900497]  CIFS VFS: Unexpected lookup error -112
Jun 12 09:07:34 myhost kernel: [479348.897468]  CIFS VFS: Unexpected lookup error -112
Jun 12 09:07:44 myhost kernel: [479358.894431]  CIFS VFS: Unexpected lookup error -112
Jun 12 09:07:54 myhost kernel: [479368.891429]  CIFS VFS: Unexpected lookup error -112

(I double-clicked at 09:06:49, so the first complaint was at 5 seconds. The window appeared at the 20 second point, but the contents of the window did not until 09:07:54. Then syslog went quiet again.)

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*: I couldn't work out how to use the gnome network tool for my needs, which include 3-4 static IPs for testing virtual hosts locally.