Intermittent Connectivity

[ToryDav]

Hi

I just installed a MS210 3 switch stack and 2 MX84s in H/A configuration using 2 ISPs and a VIP for each of those. My customer is experiencing an issue where the switch stack will alert "DNS is misconfigured, switch disabled" intermittently. I configured the DNS settings on both the MX uplinks the same on the warm and spare, but the DNS setting differ on the switches. Would this even matter? This doesn't affect the MX's they never lose connectivity, only the switch stack and therefore the clients attached to the network. This actually resolves itself after 20 minutes or so. Meraki support took a PCAP this morning working with the customer and could see DNS queries going out of the WAN interface on our MX, but could not see replies coming back from the DNS server. This does feel like an ISP issue, as we configured the MX to use Verizon DNS servers.

I'm looking for any insight and/or gotchas and best practices known around configuring DNS settings on these devices. 

Has anyone experienced this issue? You can see in the snip below in yellow over the last 1 day the intermittent connectivity for SW1 on my switch stack.

[BlakeRichardson]

@ToryDav If you hover your cursor over the orange and red part of the bar it should say what the issue was. 

[ToryDav]

Hi @BlakeRichardson, it does, it says DNS is misconfigured - switch disabled. It really does not give me anything more that that. It happens on and off while using their primary ISP, but if we send all their traffic through the secondary isp, they don't seem to have the same issues. 

Everything works as expected, but out of nowhere DNS will fail for 10 or 15 minutes and then it will resolve itself if we don't intervene. 

[SoCalRacer]

Is the MX doing DHCP?

Is the Switch getting DHCP?

[ToryDav]

@SoCalRacer The MX is doing DHCP for a couple subnets they have, including their new client subnet. Their legacy subnet is statically assigned, so some of the switch ports are on the new, and others on the old until they can re-IP all of their servers and printers. All hosts that are on the new subnet receive DHCP addresses just fine from the MX. The switch stack is Layer 2. 

[SoCalRacer]

I would check the LAN IP settings on the switch, make sure it got DHCP from the MX and 2 DNS servers configured, preferably the primary on LAN if available

[ToryDav]

@BlakeRichardson The LAN IPs on those switches are statically configured with 2 DNS servers, 8.8.8.8 and 1.1.1.1. 

The MX upstream is set to 2 servers that are Verizon DNS servers. 

[cmr · Accepted solution]

@ToryDavIF the MXs are using the ISP DNS and are fine, why not just use the ISP DNS for the switches as well?