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I am running a campus wide network of a University and experienced a very unusual scenario for my network. The problem is two folds and therefore i would like to explain that separately after briefly defining my network.

  1. My campus network is supported by a backbone Cisco 3560 Catalyst Switch
  2. The access switches are mostly Cisco 2900 family

The IP scheme that i am using is :

  1. 10.10.0.x (2 to 20) with mask of 255.255.255.192 mostly assigned to trunks and management interfaces
  2. DHCP pools for end nodes are (10.12.0.x & 10.13.0.x) having mask of 255.255.254.0

Now, the entire network was running just fine and had absolutely no issues, but recently an entire department connected to a 2900 series switch started having limited internet connectivity.

The rest of the network is working just fine, that includes all other access switches, the core catalyst switch, servers, AD (DHCP Pool and DNS as well) where i experience absolutely no problem in internet connectivity.

However, the nodes connected to this problematic switch always gives me limited connectivity, and to resolve that here's what i have already done:

  • Double checked Switch Configuration, even restored a working backup config, saved, rebooted the switch
  • The error stats on switch shows no abnormal activity
  • Checked every single port with the tester
  • Made new Ethernet connectors for both ends (switch and end nodes)
  • Reset IP & DHCP on clients using (netsh int ip reset)
  • Flushed DNS using (ipconfig /flushdns)
  • Reset WinSocket Using (netsh winsock reset)
  • Rebooted end terminals
  • Tried my clients to get an IP from DHCP which they all failed and then tried providing them with manual IPs (Same IPs as were previously assigned to these clients)

Here are the issues that i am getting:

  • Clients are unable to ping the access switch to which they are directly connected and therefore unable to ping any other network resource
  • Clients unable to ping open DNS such as 8.8.8.8
  • However, all the ports on which I have my Cisco Aironet APs running are running just fine and clients are having absolutely no issues in accessing internet resources as well as our domain based resources using WiFi
  • There is one and only particular IP from the pool which if configured to any of those clients gives internet connectivity (10.12.0.45). Now, this is just another IP address from the pool and never had any static entry in DNS or a DHCP reservation. I accidentally configured this IP and found that every client having this IP can have internet connectivity whereas they show limited connectivity for every other IP from the pool.

Now, despite trying all my technical knowledge and troubleshooting skills, I am unable to understand the underlying problem. To add to my difficulties, the smooth operation of AP ports and the internet connectivity using that particular IP address is something that makes no sense to me at all.

I have almost tried everything but i am unable to get the internet connectivity on all of those 20 clients connected to that switch.

I completely understand that my problem statement has gone so huge and boring, but I really really hope that i get some insight and help from one of our community professionals.

I would be more than happy to provide network topology or any other info demanded.

Tom O'Connor
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Omer Ali
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1 Answers1

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Do you have a spare switch you can test with? It almost sounds like ports are on the wrong vlan. I have experienced older Cisco equipment with no changes begin to stop working as installed. We replaced the switch after a ton of testing that turned up nothing. The new switch solved all our problems.

Thenooner
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