Some servers dropping network connectivity intermitantly, other servers are fine

Starting on Sunday, our network started reporting a handful of servers and devices dropping network connectivity, then coming back up, and all at the same time. We have a SQL server, two servers for Solarwinds Orion, and a couple other devices that are having the issues. Using the SQL server as an example, when it drops, I am unable to ping the default gateway, which is a Sonicwall NSA 2400, or outside to the internet. This happens with either the primary or secondary Sonicwall. Internally, our terminal server can connect to the SQL server without any issues, and our Exchange server has had no issues. I can connect to it no problem from my desk as well, but other users in the building cannot connect directly to the SQL server. The general manager can, at his desk, ping it by its DNS name, but cannot ping the IP address itself. (Yes I said that right, it will respond with the DNS name, but not IP address). Other users cannot ping either. I have checked all of the servers for potential viruses, all came back clean. I have rebooted the switch, both Sonicwalls, the DHCP server and the DNS servers. Cleared ARP cashes and flushed DNs on the servers. The servers connect to a Cisco 2930 switch, and from the switch to the Sonicwall. And this happens with both LAN and DMZ connections. There have been NO changes done over the weekend that could be the culprit. Any thoughts?
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Blue Street TechConnect With a Mentor Last KnightsCommented:
Hi signaltelcom,

Verify the Interfaces have the correct IP addresses & subnets (Network > Interfaces).

Make sure Ping is enabled on the WAN, LAN and DMZ Zones. Check in Network > Interfaces click on configure for the aforementioned Interfaces and Ping should be enabled...if not that's your issue. Then verify the Access Rules (Firewall > Access Rules) are in-place. By design this should be an automatic function of selecting the "enable Ping" within the Network > Interfaces area but we must always verify! You should see tje auto-created Access Rules under LAN > LAN, WAN > WAN, etc.

There are no such "hidden rules" that I'm aware of in SonicWALLs. All Access Rules are plainly viewable at all times.

Let me know how it goes!
sharjeel ashrafConnect With a Mentor Senior Network EngineerCommented:
i have seen the same problem on another site the problem (believe it or not), was a rule in the sonicwall pointing back to the internal LAN, it took us days to work it out and even sonicwall support didn't find it the first 10 times we called them.

from memory , the rule had the internal range, sub-net mask, and then the internal interface as the gateway, after this was removed the the unit was rebooted and so far (1 year) no problems.
signaltelcomAuthor Commented:
Did you remove the rule entirely, or just the internal interface as the gateway?
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sharjeel ashrafSenior Network EngineerCommented:
the whole rule had to be deleted. there is a way to show hidden or old rules as well, im not a sonicwall expert by any means. check both of them.
sharjeel ashrafSenior Network EngineerCommented:
please take a full backup of the config before trying anyhting.
Blue Street TechLast KnightsCommented:
Any updates with this?
signaltelcomAuthor Commented:
We checked all the rules and everything was fine. We did another simultaneous reboot of both Sonicwalls (that I found out are set up as High Availability units) and it helped. We still havent found the root cause, but so far the issue seems to have resolved itself. My Network tech is looking into it now that hes back.
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