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Here is my network connectivity:

cable modem
  wrt54g (default gateway, -- earth
Simple Switch1
|          |
|          |
|      SimpleSwitch2- neptune      
|        |      |   
|      mars  mercury
|- venus  
|- laptop
saturn (Windows AD DC)

simpleSwitch2 was hanging off the wrt54g. I moved it to SW1 during troubleshooting. Nothing described below was any different. To answer some questions:

The switches have NO configuration possible. I power cycled the entire network "stack."

earth is connected via wireless to the wrt54g.

I can ping from laptop to mars, neptune & mercury. I can ping from earth to venus, saturn & laptop.

However, pinging mars, mercury or neptune from earth gives the following result.

Pinging mars.XXX.XXX [] with 32 bytes of data:
Reply from Destination host unreachable.
Reply from Destination host unreachable.
Reply from Destination host unreachable.
Reply from Destination host unreachable.

Ping statistics for
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),

.122 is the address of the machine from which I am pinging.

Pinging earth from laptop gives this result:

Pinging earth [] with 32 bytes of data:

Request timed out.
Request timed out.
Request timed out.
Request timed out.

Ping statistics for
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

earth is a Vista machine. Windows firewall is off.

saturn is my DNS & DHCP server.

This is the wrt54g routing table(running linksys firmware)

Routing Table Entry List        
Destination LAN IP  Subnet Mask Gateway Interface   XX.XXX.XX.50    WAN (Internet)         XX.XXX.XXX.1    WAN (Internet)
XX.XX.XXX.0   XX.XXX.XXX.XX   WAN (Internet) LAN & Wireless      

Can anyone give me any ideas what the h*ll is going on? Clearly the topology is a factor

And yes, I am a space geek.

share|improve this question
Have you power-cycled both switches? El Cheapo switches are known for occasionally messing up MAC address tables. Maybe also wrt for good measure. – Aleksandar Ivanisevic Mar 26 '10 at 8:27
power-cycled the entire stack. No joy. – user18199 Mar 28 '10 at 3:42

wrt54g has an option for wireless segregation/isolation (can't remember terminology) which isolates Wireless from LAN. Worth a check to ensure not switched on...

share|improve this answer
I checked every option possible on the WRT54g, which is running stock FW, and nothing indicated such a thing. As a matter of fact, the routing table (above) indicates the opposite. – user18199 Mar 26 '10 at 14:01
  1. Is there any switching configuration on "Neptune"?
  2. Did you specify any static routing on "Earth"?
  3. Is there any switching configuration on "Simple Switch 1"?
share|improve this answer
How would I find out about static routing on a Vista box? (I don't think I did, but I don't know how to check.) – user18199 Mar 26 '10 at 13:47
you can drop to a commend prompt and type "route print" will display the routing table of the local machine. It should so any manually added routes under the section "persistent routes" – Rex Mar 26 '10 at 14:29
No manual routes. – user18199 Mar 28 '10 at 3:41

have you also checked the network configuration of each client.. specifically that the netmask is set correctly on each?

share|improve this answer
I did - it's good. Thx. – user18199 Mar 28 '10 at 3:39

This must be an issue with earth not being able to resolve either the MAC address of mars, mercury or neptune or another option is that it's a layer 3 (ip layer) issue, like routing as mentioned in bioanarchism's post.
To check these things, go to a command line (cmd from the run line):

  • Ping the host in question, even if it fails, then type "arp -a" and verify that the MAC addresses for mars, mercury and neptune are in your ARP cache. If they aren't, then one of your switches is blocking ARP broadcasts to those hosts.
  • Type "route print" from the cmd line to check the routing table on Vista. It should show an entry with: On-link xxx If it doesn't, then you have a static route configured, or the netmask on your wireless link is incorrectly configured. It should be
share|improve this answer
On the second point: it is there. On the first point: the MAC addresses aren't in the ARP cache. Clearly one of the switches aren't passing the ARP broadcast, but since I can get to mars from laptop, but not from earth, it must be the wrt54g. – user18199 Mar 28 '10 at 3:37
Is there a way to add a static route to vista? – user18199 Mar 28 '10 at 3:38
Marc, one thing I forgot to mention on the arp -a... you need to try and ping one of the "forgotten" planets first, then check the arp cache. Logically, it doesn't make sense if it's the wrt54g, that it would pass broadcasts for one switch, but not the other. It will either allow LAN access, or it won't. You can add a static entry to ARP cache and it will last until you reboot again using "arp -s <ipaddress> <mac address>". If you still can't contact the host, then something is blocking all traffic to those hosts. – Scott Lundberg Mar 28 '10 at 10:32
To add a static route, you would use the syntax as follows: route add <iptoadd> MASK – Scott Lundberg Mar 28 '10 at 10:37
Another thought. Verify that you don't have a bad switch by swappiing the two switches. If the problem follows the switch, then you have a bad switch. If it doesn't follow the switch, then I would focus on the topology of the Mars, Neptune, Mercury connections. – Scott Lundberg Mar 28 '10 at 10:40

Are there any config options for either switch?

I have been doing some testing with some inexpensive switches / routers. My opinion is that they play foot-loose, fancy-free with some of the RFC's. A couple of years ago I caught one of them fooling around with DHCP. It is almost as if they write code by using a sniffer, and duplicating the output based on what they saw in the capture.

I still have a tracert problem with my config, that runs remote desktop without issue. Remote desktop runs, I can ping one direction, but not the other. Good luck.

Can you do anything else between the machines, telnet, ftp, http, etc.

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