Reply
Ubiquiti Employee
Posts: 581
Registered: ‎10-04-2015
Kudos: 622
Solutions: 40
Contributions: 1

Intermittent Connectivity Issues? Steps to try before posting...

Troubleshooting a network can be a difficult task. Understandably, a lot of volume on the forums are attempts to identify and resolve issues related to network connectivity. To help ensure everyone gets the best help possible, we recommend you review and try the steps outlined in this document before posting about connectivity issues in the forums:

 

UniFi - Debugging Intermittent Connectivity Issues on your UAP

 

We are continually refining this guide and would love to hear any suggested edits/steps we could include to make this document more resourceful. Did something you did help you identify a network connectivity issue you were dealing with? We'd love to hear from you. 

 

Please limit any comments here to such suggested additions/revisions. 

 

Thank you!

 

-The UniFi Team

UBNT_Alternate_Logo.png
Ubiquiti Networks Enterprise Support Team

Check out our ever-evolving Help Center for answers to many common questions!

Member
Posts: 136
Registered: ‎02-22-2014
Kudos: 222
Solutions: 3

Re: Intermittent Connectivity Issues? Steps to try before posting...

[ Edited ]

This is awesome, and will help a ton of folks!

After taking a quick glance I would add some sort of an intro section regarding "Eliminating Variables", or at the very least something that suggests that troubleshooting shouldn't necessarily always begin by digging into the AP. I have worked with a couple different installations in which we were trying to troubleshoot wireless/wired issues and the access hardware attached (i.e. APs, Switches), and after much toil found the issue to be the router's Intrusion Prevention System getting bogged down in certain situations.

All that to say, I always start serious troubleshooting by eliminating the things I am not entirely in control of. It's too easy to blame slowness on the AP and get sucked into a bottomless pit of troubleshooting a device that isn't causing the issue.

New Member
Posts: 16
Registered: ‎05-22-2016
Kudos: 6

Re: Intermittent Connectivity Issues? Steps to try before posting...

[ Edited ]

Hi, there are some good tips here especially for people getting started, and it's always difficult if people come with pre-existing generic networking issues alongside needing to understand the UniFi implementation.

 

One concern I have thought - under the DHCP section:

"Please ensure that your DHCP offers and ack messages are unicast packets, not broadcast"

 

I don't think this is correct.

In the 4-way handshake of DHCP, all 4 messages are sent to the broadcast address at least in layer 3 (discover, offer, request, acknowledge). The client device without a pre-existing lease does not really have a valid IP to send to until this is complete.

 

Inform messages can be unicast because the client by then has leased an IP.

 

There are some exceptions which I list below:

 

1) Perhaps someone was thinking about renewals when the device is still within the lease time, this will start with a unicast request to the original DHCP server and fallback to broadcast if no timely response.

 

2) If the client has been pre-configured with the IP address of a DHCP server to use by another means, it may use that as a destination unicast IP address for its requests. This is an optional behaviour.

 

3) Some of the replies from the server may be unicast to the layer 2 MAC address of the client because the server knows this from the request.

There is a broadcast flag that the client can clear in its messages, to indicate that it will process a DHCP reply sent to its layer 2 hardware unicast MAC address even if it doesn't yet have a layer 3 unicast IP address usable in the normal sense. But either broadcast or unicast is a valid preference for the client.

 

4) Some messages can be unicast when a device is providing DHCP relay to a server not in the same subnet as the client (e.g. between managed switch and server).

 

Therefore arbitrarily dropping DHCP broadcasts is likely to result in some clients not receiving IP addresses at all.

And it is confusing to talk about broadcasts as being a feature of "older" or "misconfigured" routers or clients, because it's not a misconfiguration to use broadcasts, and conflating layer 2 and layer 3 broadcasts result in an over-simplification.

 

Broadcasts also support more than one DHCP server for a subnet, so that these servers can maintain up-to-date lease tables, (unless they have some back channel to sychronise their tables).

 

If there is any filtering of DHCP broadcasts to be done, it should probably be under the established principles of DHCP snooping, where the network admin can define which hosts are authorised DHCP servers (and which interface(s) are trusted in the case of managed switches).

 

https://tools.ietf.org/html/rfc2131#section-4

Senior Member
Posts: 5,692
Registered: ‎01-04-2017
Kudos: 795
Solutions: 286

Re: Intermittent Connectivity Issues? Steps to try before posting...

[ Edited ]

mdda_prl wrote:

Hi, there are some good tips here especially for people getting started, and it's always difficult if people come with pre-existing generic networking issues alongside needing to understand the UniFi implementation.

 

One concern I have thought - under the DHCP section:

"Please ensure that your DHCP offers and ack messages are unicast packets, not broadcast"

 

This is right in the document you posted.  You just contradicted yourself with your own cited reference.....lol

read a little further down next time

 

Normally, DHCP servers and BOOTP relay agents attempt to deliver
   DHCPOFFER, DHCPACK and DHCPNAK messages directly to the client using
   uicast delivery.  The IP destination address (in the IP header) is
   set to the DHCP 'yiaddr' address and the link-layer destination
   address is set to the DHCP 'chaddr' address.  Unfortunately, some
   client implementations are unable to receive such unicast IP
   datagrams until the implementation has been configured with a valid
   IP address (leading to a deadlock in which the client's IP address
   cannot be delivered until the client has been configured with an IP
   address)

A client that cannot receive unicast IP datagrams until its protocol
software has been configured with an IP address SHOULD set the
BROADCAST bit in the 'flags' field to 1 in any DHCPDISCOVER or
DHCPREQUEST messages that client sends. The BROADCAST bit will
provide a hint to the DHCP server and BOOTP relay agent to broadcast
any messages to the client on the client's subnet. A client that can
receive unicast IP datagrams before its protocol software has been
configured SHOULD clear the BROADCAST bit to 0. The BOOTP
clarifications document discusses the ramifications of the use of the
BROADCAST bit

https://tools.ietf.org/html/rfc2131#section-4   (page 25 first 2 paragraphs)

New Member
Posts: 16
Registered: ‎05-22-2016
Kudos: 6

Re: Intermittent Connectivity Issues? Steps to try before posting...

[ Edited ]

Hi goldlineIT,

 

No, I had read the RFC and understand the context of what they are discussing.

 

All 3 key points stand, that:

 

(1) broadcast and unicast are both valid behaviours which the client can indicate by use of the flag as referenced and this should not be interpreted as broadcast being somehow an "incorrect" or "old" behaviour.

 

(2) there is a difference between whether you are talking about layer 2 (MAC addresses) and layer 3 (IP addresses) as to what will be broadcast or unicast - conflating the two does not help.

To get specific, some messages may in fact be sent to the unicast MAC address where already determined but with a broadcast / undefined IP address.

 

(3) If you discard broadcast DHCP messages then you will have clients that never get connected even if they are following an allowed behaviour. This should be immediately obvious if you think about the main purpose of DHCP being to assign addresses for IP unicast

(after which it can retrieve other network settings using Inform messages).

 

It is clearly desirable to control broadcast messages in a Wi-Fi network but not at the expense of not getting an IP.

 

A "tips" article should avoid introducing topics that are too nuanced to simplify without becoming misleading, even if well intentioned.

Senior Member
Posts: 5,692
Registered: ‎01-04-2017
Kudos: 795
Solutions: 286

Re: Intermittent Connectivity Issues? Steps to try before posting...

[ Edited ]

Your reading to much into it, and missing the point. Maybe they could re-word it for less confusion but the facts remain.

Unicast is the standard for answering DHCP requests as you can quickly swamp a wireless network with broadcast messages. Most device's from this last century is going to use it. Any Linux based DHCP server will in fact act this way by default. The problem is Windows DHCP Servers does not honor unicast for some reason. (To my limited knowledge) and older linux servers. That's the issue they were addressing.

 

Nowhere in the arcticle does it say turn off broadcast completely. (At least when I just read it maybe they changed it)

Those are different key point's from what you originally posted and would of made a better argument if you went with those first.

Member
Posts: 202
Registered: ‎06-19-2015
Kudos: 37
Solutions: 4

Re: Intermittent Connectivity Issues? Steps to try before posting...

I ran into this issue lately.  If you customer is on a L3 (level 3) connection pinging google's dns servers 8.8.8.8 and 8.8.4.4 you will not get 100% return rate as L3 is being limited by google. I got around 45% success rate.

 

Emerging Member
Posts: 55
Registered: ‎01-28-2016
Kudos: 3
Solutions: 1

Re: Intermittent Connectivity Issues? Steps to try before posting...

[ Edited ]

goldlineIT, whey you say "Unicast is the standard for answering DHCP requests", you must really mean layer 2 Unicast? Specifying layer 2 versus layer 3 clears up confusion when talking about a protocol that operates at both the MAC and IP layer.  Most of the time in most conversations, unicast refers to layer 3.

Senior Member
Posts: 5,692
Registered: ‎01-04-2017
Kudos: 795
Solutions: 286

Re: Intermittent Connectivity Issues? Steps to try before posting...

[ Edited ]

rjt wrote:

goldlineIT, whey you say "Unicast is the standard for answering DHCP requests", you must really mean layer 2 Unicast? Specifying layer 2 versus layer 3 clears up confusion when talking about a protocol that operates at both the MAC and IP layer.  Most of the time in most conversations, unicast refers to layer 3.


This is clearly outlined in detail with my first post quoting RFC2131

 

 

Spoiler

goldlineIT wrote:

mdda_prl wrote:

Hi, there are some good tips here especially for people getting started, and it's always difficult if people come with pre-existing generic networking issues alongside needing to understand the UniFi implementation.

 

One concern I have thought - under the DHCP section:

"Please ensure that your DHCP offers and ack messages are unicast packets, not broadcast"

 

This is right in the document you posted.  You just contradicted yourself with your own cited reference.....lol

read a little further down next time

 

Normally, DHCP servers and BOOTP relay agents attempt to deliver
   DHCPOFFER, DHCPACK and DHCPNAK messages directly to the client using
   uicast delivery.  The IP destination address (in the IP header) is
   set to the DHCP 'yiaddr' address and the link-layer destination
   address is set to the DHCP 'chaddr' address.  Unfortunately, some
   client implementations are unable to receive such unicast IP
   datagrams until the implementation has been configured with a valid
   IP address (leading to a deadlock in which the client's IP address
   cannot be delivered until the client has been configured with an IP
   address)

A client that cannot receive unicast IP datagrams until its protocol
software has been configured with an IP address SHOULD set the
BROADCAST bit in the 'flags' field to 1 in any DHCPDISCOVER or
DHCPREQUEST messages that client sends. The BROADCAST bit will
provide a hint to the DHCP server and BOOTP relay agent to broadcast
any messages to the client on the client's subnet. A client that can
receive unicast IP datagrams before its protocol software has been
configured SHOULD clear the BROADCAST bit to 0. The BOOTP
clarifications document discusses the ramifications of the use of the
BROADCAST bit

https://tools.ietf.org/html/rfc2131#section-4   (page 25 first 2 paragraphs)


 

 Refering to unicast as layer 2 or layer 3 makes no difference unicast is unicast

 

Definition:

Unicast is the term used to describe communication where a piece of information 
is sent from one point to another point. In this case there is just one
sender, and one receiver.
Emerging Member
Posts: 93
Registered: ‎02-11-2016
Kudos: 62
Solutions: 1

Re: Intermittent Connectivity Issues? Steps to try before posting...

Feel free to rework this diagram any way you like. At least a dozen companies have developed their own with my permission based on this. https://wirednot.wordpress.com/2016/03/19/the-soon-to-be-famous-cocktail-napkin-wi-fi-big-picture/

Lee Badman
CWNE #200
Twitter: @wirednot
Member
Posts: 103
Registered: ‎02-10-2017
Kudos: 12

Re: Intermittent Connectivity Issues? Steps to try before posting...

An excellent guide thank you.  I've just been through it with my home WAP to practice.

 

I would suggest that a suggestion as to how to copy the pcaps off the WAP to your client device would be helpful for those not familiar with scp.

 

Also, I am a little unclear as to what to expect when running these commands.

cm=1; for a in 0 1; do for b in tx rx; do iwpriv wifi$a ${b}chainmask $cm; done; done; killall hostapd
cm=2; for a in 0 1; do for b in tx rx; do iwpriv wifi$a ${b}chainmask $cm; done; done; killall hostapd
cm=4; for a in 0 1; do for b in tx rx; do iwpriv wifi$a ${b}chainmask $cm; done; done; killall hostapd

 

I am assuming that after issuing each command, the WAP is broadcasting on only one chain at a time, and that if there was a problem then I would see a drop in signal strength?  I performed those three at about 2 minute intervals but did not see any real difference (about 2dB) in the signal strenght on either of the 2G or 5G SSIDs. 

 

A line or two on what you're expecting to see (if nothing wrong and/or if something wrong) would be helpful.

 

Thanks again.

 

Cheers,

Chris.

New Member
Posts: 11
Registered: ‎10-05-2017

Re: Intermittent Connectivity Issues? Steps to try before posting...

Dear piper,

 

hi I have attached System config file. i am losing connectivity while roaming only on mobile phones not on laptops. i can see mobile is moving from One AP to another but connectivity is not restoring automatically. 

systemConfig (4).png
SuperUser
Posts: 9,106
Registered: ‎01-10-2012
Kudos: 5516
Solutions: 381

Re: Intermittent Connectivity Issues? Steps to try before posting...


vannan5 wrote:

hi I have attached System config file. i am losing connectivity while roaming only on mobile phones not on laptops. i can see mobile is moving from One AP to another but connectivity is not restoring automatically. 


If the mobile is an iOS device, you might want to ensure your DITM is set to 3 - I'm not sure if DITM is available in the GUI in 5.5.x or not.

When you receive a solution to your question/issue, don't forget to mark your thread as solved and to give kudo's to the people who have helped you out!

Having wifi problems? Take a look here first: https://help.ubnt.com/hc/en-us/articles/221029967-UniFi-Debugging-Intermittent-Connectivity-Issues-on-your-UAP
New Member
Posts: 11
Registered: ‎10-05-2017

Re: Intermittent Connectivity Issues? Steps to try before posting...

Yes it is available in 5.5.24. i tried that already.no improvements. windows laptops roaming perfectly with no issues in connectivity but I have change my statement here not only the handheld devices of apple and android even apple MAC books and Ubuntu laptops are not successfully roaming.While moving devices moves from home AP to another AP devices sucessfully registered to the AP but connectivity between the gateway is not getting restored.
Either we have to manually shutoff the wireless card and connect it again no other go. Is the current status
New Member
Posts: 11
Registered: ‎10-05-2017

Re: Intermittent Connectivity Issues? Steps to try before posting...

Help me in sorting out this issue.
SuperUser
Posts: 9,106
Registered: ‎01-10-2012
Kudos: 5516
Solutions: 381

Re: Intermittent Connectivity Issues? Steps to try before posting...


vannan5 wrote:
Help me in sorting out this issue.

Take a look at 2 and 4 on this poster:  http://www.revolutionwifi.net/revolutionwifi/2016/6/grab-the-new-wi-fi-design-poster-today

When you receive a solution to your question/issue, don't forget to mark your thread as solved and to give kudo's to the people who have helped you out!

Having wifi problems? Take a look here first: https://help.ubnt.com/hc/en-us/articles/221029967-UniFi-Debugging-Intermittent-Connectivity-Issues-on-your-UAP
Member
Posts: 220
Registered: ‎04-11-2017
Kudos: 33

Re: Intermittent Connectivity Issues? Steps to try before posting...

unfortunatly for me.. intermittent connectivity issues started happening when tempretures dropped below -20 celcius... since then its been hell. When the sun rises all the mesh's start connecting.. when the sun goes down and so does the mesh's.. we got -41 celcius  a few days ago.. nothing.. not in isolated state.. but disconnected !.. curiously.. the only one going strong is my unifi mesh pro.. connected directly to the switch.. it never died... also as weird as hell.. i got 2 mesh's in pure line of site.. perhaps 200' distance from the mesh pro.. one doesnt even see the mesh pro, cant choose it as uplink. the other one thats  farther like 500' away.. he connects.. other little things like when i log in the dbm would be way lower than i configured like -70 when its supposed to be at -90.

The wifi disconnects me most of the time for no apparent reason.. if i change a channel on 1 mesh a few mesh's down.. the whole line will go into provisionning mode and most likly the wifi will reset. The preferences option in the username top right always comes back to defaults no matter what i do... so thats what grinds my gears today!

Highlighted
New Member
Posts: 5
Registered: ‎10-04-2017

Re: Intermittent Connectivity Issues? Steps to try before posting...

I have an issue on a site, that every wifi device only connected for 4-10 seconds, and then it's disconnected. Tried using tplink, dlink, no luck, and finally i choose UAP AC LR. But the problem still persist. (all clients, iphone 7, samsung smart tv, dell laptop with intel 8260AC card, galaxy note 5, no luck)

 

And the i use cheapy pocket tp-link with openwrt fw, it works flawlessly without any disconnection issue! 

 

Anybody have an idea what happened?

Somebody attacking my site using high power wifi? I plan to sniff wireless frames, next week.

 

How to solve this problem? 

 

5ghz 802.11ac on UAP-AC-LR seems fine without problem

Reply