topic Re: ARP conflicts on a MSM760 controlled wireless network in M and MSM Series

ARP conflicts on a MSM760 controlled wireless network

holunde — Fri, 08 Jul 2016 10:01:48 GMT

I run a highschool network where wireless access is controlled by a HP MSM760 controller.
It controls at the moment 58 HP MSM430 wireless access-points, and I'm very pleased with it.
Also I've set the MSM760 up so that it's two networkconnections are on two different VLANS.
One is used for students and guests, the other for administration, teachers etc.
Each VLAN has it's own internet-connection and it's own SSID. The MSM760 is not the DHCP-server
for any of the two VLAN's.
We use a simple authentication scheme and all in all we are very pleased with it all.

BUT, on some of our main switches, also HP (HP A5500-24G-EI and HP A5120-48-EI) I see some worrying
stuff in the log quite often. There are many other switches, mostly HP V1810-48G's, but it's the
two first mentioned, that complain. And it must have to do with the fact, that people are moving around the
campus with their phones, for example, and therefore moves from one access-point to another.
The log-entries look something like this (from the HP A5500-24G-EI main switch):
----------
Jun 12 11:49:25:377 2016 ARP Notification ARP_DUPLICATE_IPADDR_DETECT Detected an IP address conflict.
The device with MAC address 285a-ebd4-8cba connected to GigabitEthernet1/0/8 in VLAN 1 and the device with MAC
address 285a-ebd4-8cba connected to GigabitEthernet1/0/3 in VLAN 1 are using the same IP address 10.0.14.64.
----------

So the device with mac 285a-ebd4-8cba has moved from one sub-switch to another, and I get this notification.
Sometimes I also get a warning:
-------
Jun 12 11:49:46:998 2016 ARP Warning RATELIMIT The ARP packet rate(496pps) exceeded the rate limit(50pps)
on interface GigabitEthernet1/0/30 in the last 60 seconds.
-------

This is more worrying and comes up from time to time. But apart from that everything works just fine.

Is this behaviour inherent in the way, that I have set things up?
Or have I done or understood something wrong?

I can of course supply much more detailed information, if someone is willing to give me a reply on this.

Hans Otto Lunde
Teacher and Network-administrator
Egmont Højskolen
Denmark.

Re: ARP conflicts on a MSM760 controlled wireless network

johnk3r — Fri, 08 Jul 2016 13:17:26 GMT

Hi !

What is the firmware version of 5500 ??

There is an update that fixes the problem ARP and MAC informed below...

Re: ARP conflicts on a MSM760 controlled wireless network

holunde — Sun, 10 Jul 2016 09:52:14 GMT

Software Version
5.20.99 Release 2220P10

Hardware Version
REV.C

Bootrom Version
707

Re: ARP conflicts on a MSM760 controlled wireless network

johnk3r — Mon, 11 Jul 2016 13:13:43 GMT

I recommend you upgrade the switch !!!

Below the releases that should solve your problems:

A5500EI-CMW520-R2221 Changes in Operations

1. Changed the maximum ARP rate on a port that is enabled with ARP detection from 50 pps to 400 pps.

A5500EI-CMW520-R2221P20

201510200101
Symptom: The switch prints a message indicating an IP address conflict when a newly online wireless client obtains the IP address of a wireless client that just went offline.

Condition: This symptom occurs if the following conditions exist:
                   Wireless clients obtain IP addresses through DHCP.
                   A wireless client comes online after another wireless client goes offline.

Re: ARP conflicts on a MSM760 controlled wireless network

holunde — Wed, 13 Jul 2016 08:40:34 GMT

Thanks John

This looks af if it's the excact issue, that I'm dealing with.
I found a newer version of the firmware, A5500EI-CMW520-R2221P25, which should be the current one.Have one question though, since there are a lot of reports on how terrible the upgrade proces is on these switches.
It seems af if I could upgrade simply by using the web-interface to upload the A5500EI-CMW520-R2221P25.bin file and setting it as the "Main". Do you know if this is correct, and will it preserve my settings?
Would hate to have it remove all my settings, as this switch is the most important one in my network.......

Re: ARP conflicts on a MSM760 controlled wireless network

johnk3r — Thu, 14 Jul 2016 01:39:54 GMT

Hello Friend !

I recommend the following update process:

1 - Backup the switch configuration file.

2 - Download the firmware "5500.EI-4800G_5.20.R2221P22" after update the bootroom file (btm) and binary (.bin);

3 - If the above process worked, download the firmware "5500.EI-4800G_5.20.R2221P25" and only update the binary.

Note.: Perform updating by CLI.