MR30.6 - Multiple DHCP servers detected

[RaphaelL]

Hi ,

I'm testing MR30.6 in a Lab.  Since the upgrade , my event logs are flooded with : 

Vlans are configured on the MX , and the MX relays the DHCP requests to multiple DHCP servers , so of course multiple DHCP responses will be received. 

Support says this is expected... 

Anyone experiencing the same thing ? That doesn't make any sense to me... Clients connected to the MX or the MS on the same vlan do not generate these logs despite receiving multiple dhcp offers.  

[RaphaelL]

Mmmm.... we were having these before MR30.X , still I don't think that this makes any sense. Or am I missing something ?

[cmr]

Well, I guess the event log is just telling you that you have set up multiple DHCP servers...  I guess you could just filter it, but that doesn't explain the difference in behaviour compared to the MS.

[alemabrahao]

I've seen this behavior in much older versions than this one. Is this really expected? I can't say, but I've observed this behavior since 2015 as far as I can remember.

[alemabrahao]

Maybe it will help you.

https://documentation.meraki.com/MX/DHCP/Tracking_Down_Rogue_DHCP_Servers

[cmr]

@RaphaelL this is in the original 30.6 fix list, but is now not...

• Multiple DHCP servers detected when clients use DHCP relay (Wi-Fi 5 Wave 2, Wi-Fi 6 and Wi-Fi 6E APs)

[RaphaelL]

Support told me that this fix is for single DHCP relay ( one DHCP reply ) and not for multiple DHCP servers like my setup 😣

[cmr]

It does say multiple DHCP servers and it is now not fixed, so I wouldn't be so sure...

[RaphaelL]

This is the reply I got : 

After discussions with a few different members of my team that worked on the original bug report, the reason why the fixes weren't working for us here is because I originally misinterpreted what the report sought to fix. The original report was related to seeing the Multiple DHCP servers detected in the event log when only one dhcp server was specified as dhcp relay. In short, activating any DHCP relay at all even with one relay agent upstream would trigger this and that behavior specifically was what was fixed*. With that said, it was explained to me that since more than 1 DHCP server is specified as a relay for the same vlan upstream in this situation, then the Multiple DHCP servers detected alert is actually true in this case since clients could receive offers from two separate servers, and therefore the DHCP server detection feature is functioning as intended in this case.

+ They had me test a private build ( 30.7 ? ) which didn't fix anything. Per support there is nothing to fix since this is expected. This is debatable. 

*Not fixed since removed from the changelog as you mentionned