[SOLVED] Slow DHCP between Meraki MS250 => Cisco SG220 => Macbook(s)

[Marco_812]

Hello:

I'm serving DHCP from an MS250 layer 3 interface down through a Cisco SG220 switch and ultimately to some Macbooks. If I've got a Windows machine connected it picks up the DHCP info fairly quickly but the Macs are very slow to pick up the DHCP and usually self-assign an IP address before eventually obtaining an IP address from the Meraki

Does anybody have any tips/ideas to speed DHCP up for the MacBooks, especially perhaps in the settings for the Cisco SG220? I'm sure some of it is on the Mac side, especially if I'm using a USB to RJ45 adapter. A thunderbolt to RJ45 adapter, or if I've got an older MacBook that actually has a network port will get better results but will still self-assign an IP address before getting one via DHCP

On the layer 3 interface I have no boot options set, and multicast routing is disabled

The port on the Meraki is set to Trunk, with RSTP enabled and Trusted Mode not enabled

On the Cisco SG220 I can ping the layer 3 interface with no problem, not really sure what else I should be looking at

Any tips appreciated, or if you can point me in the direction of what I should be researching that works too, thanks much!

[BlakeRichardson]

@Marco_812  I would start running a packet capture, then connect on of the Macbooks, give it time until the device self assigns and then end the packet capture.

Then you can have a look at that capture and it should give you an idea of what is going on. I wonder if there is some odd routing loop on your network thats been created by accident. 

If you are unsure how to read packet capture files upload it here and I am sure someone can have a look.

[jdsilva]

Totally agree with @BlakeRichardson on this one. Packet capture is the way to go. I would also capture on the MS to compare to the capture from the Mac. 

https://documentation.meraki.com/zGeneral_Administration/Cross-Platform_Content/Packet_Capture_Overv...

[cmr]

Can you connect a Mac directly to the MS250 to eliminate the Cisco SG (or prove it)?

[PhilipDAth · Accepted solution]

Have you configured the port that the Mac is plugged into as an "access" port or configured the equivalent of "port fast"?

I'm not familiar with that model switch, but look for those things

[WD]

OS X 10.9.4 fixes a long-standing bug in Mavericks related to wi-fi connections coming out of sleep.

http://support.apple.com/kb/HT6281?viewlocale=en_US&locale=en_US

Also if the Mac have many AP in their list try to drag your AP higher as this can cause delays.

[Marco_812]

Hey thanks everybody, didn't mean to drop out on ya but I had a little unexpected Covid break and I'm back on it and I believe I have it solved!

Big extra thanks to @cmr and @PhilipDAth for the clues I needed. Hooking the MacBook up directly to the Meraki MS250 did result in getting an IP address almost instantly, no interim self-assigned address. I should have read Philip's response a little more closely as I went off in my own direction researching the SG220s which led me to the Port Fast setting you referenced, although in the SG220 this is referred to as Edge Port, at least in the GUI

I changed the port setting to Edge Port for a couple of the ports, connected the MacBook and Boom! 4 seconds to an IP address, even with these clunky USB to Ethernet adapters

Obvious in hindsight but it turns out this wasn't a problem with the Macs at all. I had noticed that the SG220s were slow to pick up an IP address as well, but I didn't connect the dots

On Cloud 9, this has been a thorn for several months. Wondering if I can pull a Costanza and leave work early on a high note

[cmr]

Excellent @Marco_812 , glad you got it working, definitely time to go home early now for a well earned 🍺