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I have recently been made the IT administrator in our organization. We have in-house servers; DNS, Windows Authentication, etc, and we have 2 switches with around 25 computers and devices connected to the internal network. 

There are problems with the 'older' computers, by older I mean that they have been present in the network for a longer period of time. These older computers randomly disconnect from the network; Internet not available. They completely lose the Default Gateway and Connection-specific DNS suffix, and the only solution is to do the following;

ipconfig /release
ipconfig /renew

*After the commands, the computers have internet; they still use the same IP address but they now receive the gateway and DNS suffix again. Example below;

after internet drop;

Connection-specific DNS Suffix  . :       
Link-local IPv6 Address . . . . . : X       
IPv4 Address. . . . . . . . . . . : 192.168.1.200 
Subnet Mask . . . . . . . . . . . : 255.255.255.0    
Default Gateway . . . . . . . . . :

after ipconfig/release and ipconfig/renew (internet available):

Connection-specific DNS Suffix  . : domain-org.local    
Link-local IPv6 Address . . . . . : X    
IPv4 Address. . . . . . . . . . . : 192.168.1.200    
Subnet Mask . . . . . . . . . . . : 255.255.255.0    
Default Gateway . . . . . . . . . : 192.168.1.6

I am suspecting that there may be a problem with the DNS server which is randomly disconnecting these users. In some computers it happens at specific times; at around 01:30PM.

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  • Please note that protocols above the transport layer and host configurations/issues are off topic here. DHCP and DNS are only on topic when used on an on-topic network device. The vendor needs to offer optional, paid support, see the help center.
    – Zac67
    Nov 13, 2023 at 10:23

2 Answers 2

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I am suspecting that there may be a problem with the DNS server which is randomly disconnecting these users. In some computers it happens at specific times; at round 01:30PM.

(Bordering on this board's scope)

Nope. A DNS server can't usually do that. A DNS service does not talk to network devices (in extenso: switches) to make them bounce-off connected end systems. Other/Special software/services on servers could do that, e.g. those from the area of Network Access Control, but such setups require quite advanced cooperation between NAC admins and network admins - too far fetched, here.

You might want to check if the DHCP scope for that subnet is exhausted, and if the DHCP service for that subnet is running reliably.

A DHCP client, if can't renew its lease in timely fashion (either because the DHCP service is unreachable or won't answer, or because the DHCP services keeps returning DHCPNAK messages), will eventually have to reset its IP interface, forget everything it learned from DHCP options (such as gateway information, connection specific DNS domain, recursive DNS servers), and eventually start over and hope to be given a new DHCP lease.

If the DHCP service for this subnet is running on a device covered by the scope of this board (a router, a L3-Switch, possibly a firewall) we might be able to help; you would need to show us (sanitized) config snippets of that DHCP service's configuraton and running state.

If the DHCP service is running on a server, ServerFault (right next door at https://serverfault.com/) might be a better place to ask.

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You're not provided much detail on your network and end-node handling (infrastructure, firewalls, ...).

The general troubleshooting steps are working your way up the network layers:

  1. Physical layer - rule out cabling/interface/port problems, do link LEDs light up? (doesn't seem to be the case here)
  2. Data link layer - make sure the connected nodes are visible in the intended VLANs, check the switches' MAC tables
  3. Network layer - are the IP addresses correct? can you ping important hosts by IP address - default gateway, DHCP server, DNS server, file server?
  4. Transport layer - can you query the DNS server(s)? connect to servers by IP address on the socket level?
  5. Application layer - do DNS names resolve? can you access servers by name?

Since a DHCP renew solves your problem, I suspect something like an incorrectly configured or malfunctioning DHCP snooping. If you see a problem in the network layer (step 3) that would match. Another possibility is a broken DHCP server that doesn't honor renewal requests and only processes full DORA cycles.

Alternatively, you should find out what happens in your network around 1:30pm.

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