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A few days ago I rewired two racks at my local datacenter. They are side by side and have about 40 servers.

I was using an old office type switch and two Dell PowerConnects 5324 and I wanted to remove the old switch (which had about 80% of the machines hooked to it) and rewire everything to use the two PowerConnects instead (which had about 20% of the machines hooked up to them).

Basically what's happening is that I can't SSH/FTP/Ping/etc from the servers (locally) to each other, but ALL servers are accessible remotely. Some will connect fine, but others won't (error: no route to host). It's extremely odd because the servers are all connected to the two Dell PowerConnect 5324 Switches, and the two switches are connected to each other. Most servers can access each other but some, seems very randomly picked, can't connect to other random servers even if they are on the same switch.

Ex:

Same Switch, Rack #1:

Server 1 can connect to Server 2 and Server 3 Server 2 can connect to Server 2 but not Server 3 Server 3 can connect to Server 2 but nto Server 3

My guess is that the PowerConnects have some type of a route cache, which is telling them that the old (office style) switch is handling the traffic for the request.

I've rebooted the switches, and router and it made no difference.

I'm stuck scratching my head here and I would really appreciate some feedback. Is there some type of cache on here that I can clear? Could it be the router doing this?

No settings were changed on the servers, router or switch. Firewalls are not causing this.

Thanks for your help, Luc

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any VLANs set up in either the old switch or the new ones? –  Devnull Sep 13 '10 at 0:47
    
No. They are all on globally accessible IPs. –  Luc Sep 13 '10 at 0:49
    
Are all the subject IPs on the same IP net? –  user48838 Sep 13 '10 at 0:54
    
They are on the same router, and there are two C classes. –  Luc Sep 13 '10 at 1:26
    
Smells like VLANs to me too –  Rob Olmos Sep 13 '10 at 2:21

1 Answer 1

It sounds like there may be VLANs set up on the switches. That's probably the first place to look. If so, mapping out the VLANs will probably shed light on what you are experiencing.

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Does anyone know how to reset the VLAN on the PowerConnect 5324? –  Luc Sep 13 '10 at 3:17
    
Based on the configuration example of: "interface ethernet 1/g3 switchport mode general switchport general pvid 10 no switchport general acceptable-frame-type tagged-only switchport general allowed vlan add 10,20 exit" It appears the vlan command is "switchport general allowed vlan add 10,20" where "10.20" is the vlan identifier. You may want to make sure all the ports either do not have the command associated or are set to the same vlan identifier - assuming you want to switch(es) to be "flat" across the switching plane. –  user48838 Sep 13 '10 at 4:14
    
One more try... It appears the vlan command is "switchport general allowed vlan add 10,20" where "10.20" is the vlan identifier. You may want to make sure all the ports either do not have the command associated or are set to the same vlan identifier - assuming you want the switch(es) to be "flat" across its switching plane(s). –  user48838 Sep 13 '10 at 4:19
    
Thanks guys. I'll hitup the data center tomorrow and try it. –  Luc Sep 13 '10 at 6:47

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