Networked computers can't see 2 of my Macs

Please describe or diagram your network topology. Include all switches, hubs, routers, cable modems, DSL modems, wiring runs, patch panels, etc.

Also identify how each computer is connected to the network: wireless or wired, speed (10, 100, 1000), etc.

Finally, have you used Network Utility.app and its Ping tab to test whether the addressed host responds to pings or not? Network Utility is a standard Apple app, located in /Applications/Utilities/.

Macbook and Mac Mini can see the iMac, PC laptop and Dell mini

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Can the Macbook and Mac mini see each other?

Model numbers for cable modem and router?

Please describe exactly what program you're using to determine whether one computer can or can't see another.

In this list:

Dell mini can see the iMac and PC laptop
Macbook and Mac Mini can see the iMac, PC laptop and Dell mini
iMac can see the PC laptop and Dell mini
PC laptop can see the iMac and Dell mini
Dell mini can see the PC laptop and iMac

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The first and last items are logically identical, so the last item is redundant.

What were the results of the ping test?

Are there any other nearby wireless networks, which might be open (unsecured) and the Macbook or Mac mini might be automatically connecting to?

When you say all 5 computers are using DHCP, what is assigning the DHCP addresses? Is it your router, or your cable modem, or does your cable company assign you some static addresses, or is there a DHCP server upstream from your cable modem? To find out, use the Network pane of System Preferences to see the Router address.


Things to try.

1. What does Bonjour Browser show? Run it on each Mac and compare the results. Enable screen-sharing on each Mac (or disable then re-enable) and see what changes, if anything.
http://www.tildesoft.com/Programs.html

2. Does the whatismyip website show the same IP address for all 5 computers? If not, are they all addresses assigned to you?
http://whatismyip.com/

3. On either the Macbook or Mac mini, disable wireless, enable ethernet, and connect it to the router with an ethernet cable. Does this change the visibility of this computer relative to the trio that can all see each other? From your description, the trio of mutual visibility is iMac, PC laptop, Dell mini.

4. On either the Macbook or Mac mini, temporarily disable the firewall. System Preferences > Security > Firewall, then click the Allow all incoming connections radio button (Leopard), or click Stop after unlocking the pane (Snow Leopard).


Things to compare, and even consider posting.

On each of the 3 Macs, launch Terminal.app, then enter or paste the following command-line:

This command lists a number of networking parameters, for every known (active or inactive) network interface. If you know something about networking, make sure all active interfaces are on the same subnet with the same subnet mask.

flyersgl said:

I could not figure out what to enter on the ping test, so I did not perform.

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Enter the IP address of the target computer. A total of 5 pings should suffice.

For example, in your original post, the iMac could not see the Mac mini, but the Mac mini could see the iMac. So step 1: run Network Utility on the Mac mini and enter the iMac's IP address to ping. Step 2 reverses that: run Network Utility on the iMac and enter the Mac mini's IP address to ping.

Any computer should also be able to ping itself by entering its own IP address. It can also ping itself by entering the special self-referencing address 127.0.0.1.
http://en.wikipedia.org/wiki/Localhost

1. Bonjour Browser showed exact same services for all 3 Macs.

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What you should be looking for is the presence or absence of all 3 Macs. Did every Mac show a total of 3 Macs: itself and two others?

If all 3 are visible from each Mac running Bonjour Browser, then the network is fundamentally working.

The next step would be to look at the services that each Mac is providing. If a Mac is not providing a sharing service, then it won't show up in Finder's sidebar. Two things that I'm certain cause a host to appear in the sidebar are file-sharing and screen-sharing.

Exactly what are your non-visible Macs sharing, i.e. under which services does Bonjour Browser list each computer?

I did not enable/disable screen sharing as it seemed to require iChat set up, which I haven't done and wouldn't otherwise be inclined to.

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The screen sharing service is enabled and disabled on the Sharing pane of System Preferences. It should not require iChat setup, AFAIK. Can you explain or describe why you think it does?

I wasn't asking you to use iChat to connect to any of the computers that were sharing their screens. All I wanted was to enable and disable a service that does two things: 1. show up in Bonjour Browser, 2. show up in Finder's sidebar.

2. same ip address for all computers.

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This indicates they are all on the same subnet, going through your router and cable modem. It confirms they aren't accidentally using some other wireless network.


Given the rest of your results, the only other thing I can think of is that 'ipfw' is turned on, and is blocking something that the application firewall would let through. See the following, and consider using one of the apps to make sure ipfw isn't enabled.
http://www.hanynet.com/comparison.html


EDIT:
One more thing. On the computers that can't see your "missing" Macs, bring up the Finder Preferences window, choose the Sidebar icon, and make sure the "Bonjour computers" item is checked under Shared.