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halmartin / meraki-builder

Scripts and tools to assemble firmware images for various Meraki MS switches and MX routers
GNU General Public License v3.0
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DHCP Broadcast not passed through #13

Closed ben-oxley closed 3 years ago

ben-oxley commented 3 years ago

Whilst I've not fully tested this yet, I seem to see a weird behaviour when following these steps:

  1. Connect DHCP Server and upstream network to Port 1.
  2. Boot up MS220-8P
  3. Connect POE powered device (MR-18 flashed with OpenWRT) to Port 2.
  4. Device on port 2 does not acquire an IP address.

I suspect that either the switch is not passing on DHCP packets or probably more likely isn't forwarding broadcast packets?

I'll continue to investigate with some wireshark etc.

halmartin commented 3 years ago

Can you MITM the upstream network port of the MS220-8P and see if you see the DHCPREQUEST from the MR-18?

I have not had any issues with downstream devices obtaining a DHCP lease on my MS220-8P.

ben-oxley commented 3 years ago

Will do! I'll get back to you with it, as soon as I can get something to MITM the traffic.

halmartin commented 3 years ago

You don't need to necessarily MITM the traffic, you can run dnsmasq (and optionally tcpdump) on the upstream device and you'll have a view of DHCP request/replies.

e.g. on the upstream device connected to the MS220:

ip addr add 192.168.10.1/24 dev eth0
dnsmasq -a 192.168.10.1 -d -F 192.168.10.10,192.168.10.20,2h -i eth0

dnsmasq will then show DHCPDISCOVER, DHCPOFFER, DHCPREQUEST, and DHCPACK in stdout. Replace eth0 with your Ethernet interface device name.

ben-oxley commented 3 years ago

I don't have the results of a tcpdump/similar for you yet, but check this out. The issue turns out to only be on port 2 of the switch (Ports 1, 3-8 all seem to work fine!). It's possible that its just a dodgy port and that port 2 just isn't usable.. I've got another switch that I need to flash at some point soon so I'll try that and see if it has the same problem and report back.

halmartin commented 3 years ago

This is the same switch you were having PoE issues on, right? If I remember correctly, you said that you tried other ports and PoE was still non-functional, so there may indeed be something wrong with the 220-48LP.

It's strange though, because I would expect the same issues on the 320-48LP/FP, and other people have not reported any issues with these models. The only differences I know of between the 220-48 and 320-48 are the hot-swap power supplies.

What does /click/switch_port_table/dump_pports say when you have a device connected to port 2? I assume the port is at least negotiating a link.

It might also be worth taking a look at /click/switch_port_table/dump_pport_vlans; maybe I've got an error in an initscript and the port is not being initialized on VLAN/PVID 1.

ben-oxley commented 3 years ago

Sorry no, this is on an MS220-8P (not 48).

I'll take a look at the dump_pports tomorrow and see what it says.

ben-oxley commented 3 years ago

Seems to be a dodgy port on the 8p, just flashed a second one and port works just fine!