AP530 blocking arp requests from wired network

[Marco Wessel]

Hi,

For the longest time now (ever since I started using them, really) I've been having issues with intermittent connectivity loss on my AP530s. A station would be happily connected to the network(/internet), and then suddenly stop being able to send or receive any data to and from remote hosts. This of course can be easily traced to the default gateway being unreachable: pinging it leads nowhere.

Now, I've finally figured out why this happens: the AP530 blocks ARP requests from the wired network, and my gateway re-arps periodically. When it does that, it clears its own arp cache and re-arps anything that was in it. Obviously, with the AP blocking the incoming ARP request, no response is ever received from the stations and as a result all traffic outside the subnet halts until the station itself decides to re-arp the gateway (or I delete its cache entry manually).

Unfortunately, I can not turn off the re-arping feature on the gateway. I can set it to between 2 and 120 minutes, and that's essentially it. Also, this wouldn't solve the problem entirely because arps coming in from other hosts on the network would still be lost.

So it seems the problem could be solved entirely by setting the AP530s to not block ARP requests from the wired network. However, I can't find a setting for this.

Does anyone know if this can be set in the config? Or must I kick someone at HP for not making this a configurable option?

Regards,

Marco

[Marco Wessel]

Additional info: this only happens on WPA or 802.1x-encrypted SSIDs. I set up a test SSID with no encryption on which all arps were correctly being forwarded. It also works fine with WEP encryption.

I forgot to mention how I tested this: I set up two computers in the same VLAN, one wired one wireless. Made sure they did not know eachother's MAC addresses (arp -d) and pinged the wireless computer from the wired computer. No dice (and no arps on the wireless side of some sniffing). The second I do the reverse (ping wired from wireless, which works) the first ping starts showing responses (and the sniffer shows arp packets being sent from my wireless computer).

[Adam Ryan]

Hi Marco,

We are also experiencing the same problems with the AP530. We recieve intermittent connectivity loss all the time on 5 AP530's we have on site (we have 50+ AP420's and never have an issue, we also have 2 AP530's in a bridge setup that never has an issue).

I am glad that you have identified what may be the issue in the ARP setting - and of course we would also love a fix for this.

To support your argument also, we have 2 AP530's in a bridge setup that are not on a VLAN and not using WPA or 802.1x. The other 5 AP's are using 802.1x - these are the 5 we have the connection issue with.

I will follow this post closely to hopefully one day have a result!

We have just purchased one MSM422WW to hopefully replace the AP530's and AP420's in the future after we test it also.

Thanks again for your work!

Adam.

[Marco Wessel]

Hi Adam,

Thanks for confirming that I am not, in fact, the only one having this problem with the 530s. I don't have any 420s myself but I'll believe they work fine. They must be based on different code.

I've found it isn't even specifically ARP-- in some cases it blocks /all/ broad- and multicast frames. And then in some cases it'll work fine even with WPA. I haven't been able to figure out what's triggering the faulty behaviour so far.

I have kicked someone at HP and they seem to be taking a serious enough look at it. Tomorrow I will test varying configurations to see if the problem is limited to certain combinations of encryption types (CCMP/AES, etc.). We'll see what happens..

Let me know how the MSM422 works out-- I'd be interested in them even if only because they do 802.11n with 4 radios while still getting power from the switch. Of course if they suffer the same problem I'll have to look elsewhere. I suspect they'll be based more directly on the original Colubris code so they'll probably be fine also.

[Adam Ryan]

Hi Marco,

Let's hope someone at HP can help out. I used to have a very good contact at HP who was VERY active on these forums, but has now moved on. It would have been a very interesting problem for him to try and work out.

We are anticipating the arrival of the MSM422 to hopefully get us out of the flaky wireless situation we have in the given area. It is hard when you have 1000+ connections a day and it only work 1/8th of the time!

I will keep you posted as to how the 802.11n works also - as this is what we will be primarily trying to achieve. We will also obviously use the second radio as our 802.11g network. It will be interesting to see how they work along side each other. I guess if we use 5Ghz for the n radio it should be fine.

Do you use both radios in the AP530? We did and then disabled the second one as we thought they may have been clashing with each other. Which obviously did not solve our problem.

Keep me posted on your progress as you are spending a great deal of time on the problem and searching for the ultimate solution!

Thanks again, talk soon.

Regards,

Adam.

[Marco Wessel]

Adam,

The 422 should have three radios, no? I'm finding the specs on these things rather more sparse than the pre-colubris models. For instance, there seem to be no manuals online just yet. (This is always my prime source of information: the manual tends to detail exactly what can and can't be done whereas the data sheets usually just say 'this device will change your life forever'.

Yes, I use both radios on the 530APs. I too tried disabling both of them while checking for specific requirements to trigger this issue to see if it changed anything for the other-- it did not.

I'm spending a great deal of time on this indeed-- if 'the internet' doesn't work, most people seem to think that I did something wrong...

Can I point my current HP contact for this issue at you to see if there's anything specific about our setups that could be the cause?

[Adam Ryan]

Marco,

I would be more than happy to help assist and find a solution!

The MSM422 does have 3 radios. I have attached our spec sheet that was given to us - as you say... this is the one 'that will change your life' spec sheet.... but it does have some detail. No manual though! When I recieve it I will try to send you a copy of the manual (if it comes with one!)....

Let me know what you want to organise as far as keeping in touch with your HP contact.

Regards,

Adam.

[Rolland_4]

Hi Marco and Adam

Did you receive any news from HP regarding this problem ?

We have the same troubles with 4 AP530s using WPA SSID

Regards

Francois

[Adam Ryan]

Francois,

I have not heard anything as yet.

Im not sure how Marco is going, hopefully he can post back some information regarding his trials.

We have also seen some errors with the MSM422, but after the unit was sent back to the supplier and found not faulty we are working on our network to see if it is something else causing the issues. The issue we had with the MSM422 was when we plug the unit into our LAN it temporarily disabled our entire network (over 130 devices!!!), it is very strange!!! It physically stalled our network, as if it was a spanning tree effect.

I rang HP support and they told us to disable DHCP support. We could not find this in the MSM422 to disable it, so we are back to square one also!

I am very interesting in finding a solution to this as it will fix a lot of our errors!

Catch up soon.

[Rolland_4]

Adam

I could not find any DHCP support in AP530 either : the only DHCP option concerns the LAN configuration of the AP, but we are using static IP.

I did already try to enable or to disable spanning tree on all AP530s, without any effect.

As we do not have any MSM422, I am unable to help you concerning the troubles you have with this AP

Regards,

Francois