Slow Internet on Random IP Addresses?

[supra21]

We have had this problem on and off for a long time but could never find a solution to it. Sometimes we will get reports of slow internet speeds on wired or wireless devices of any type. After doing the normal troubleshooting steps the final step we now do is delete the ip address of the reported device from dhcp then exclude that ip from distribution. We then renew the ip on the device so it gets a new one and the internet speeds are back to normal.

The odd thing is after a long time has passed we have tried using that the excluded ip by assigning it statically to another device and the internet speed is fine....it really baffles me.

 

We have:

Zyxel switches across the school

RM network (cc4.5)

Windows Server 2019

Smoothwall

 

We do not have any bandwidth limiters in place either, so I am really not sure where the problem would lie. Any suggestions would be great.

[robyholmes]

If you unplug the device, wait 30 seconds then plug it back in while it's still on (Or disconnect wireless for wireless devices), goes it sort it? Or do you have to get a new IP address?

[supra21]

Yes we initially try this but issue remains until device gets a new ip address.

[kennysarmy]

Can you bypass the Smoothwall when it happens?

 

How are you proving "slow internet" ? By using an online speed website?

[supra21]

Yes we have tried adding the IP address in question to exceptions section in Smoothwall to bypass filtering issue still remains.

When the device is brought to us it's so slow it can take minutes to resolve the gmail inbox or a google search. Going to fast.com shows speeds of 100kbps to 1mbps before we change the ip. After the device gets a new address speeds go to 35-45mbps on wifi and 500-800mbps cabled in (we have a BT 1gbps connection).

[Michael]

This comes across more of a DNS issue or possibly even VLAN. Be interesting to see when you have a problematic device, which DNS server it's resolving first.

[supra21]

At the moment the most common device having this issue are our chromebooks. I had one a few minutes ago, we set the DNS servers to google's and still super slow (150-300kbps). After giving it a new IP address internet speed is now 30mbps.

The chromebooks do have their own VLAN.

Edited April 19, 2021 by supra21

[Michael]

Another aspect to check is whether it's connecting to a different AP, seeing as it's wireless. This could well be a switching/VLAN issue if you've set it to Google DNS manually as a test.

[supra21]

I doubt it's a different ap as the IP changes made to the device are done in the same location as where the issue is exhibiting itself. Also we have other devices in the same location with internet speeds performing as expected. If it were to be a switching/VLAN issue where would be a good place to check?

This issue does also occur on windows pc's cabled in but it's more of a rare occurrence with those.

Edited April 19, 2021 by supra21

[Michael]

I doubt it's a different ap as the IP changes made to the device are done in the same location as where the issue is exhibiting itself. Also we have other devices in the same location with internet speeds performing as expected. If it were to be a switching/VLAN issue where would be a good place to check?

This issue does also occur on windows pc's cabled in but it's more of a rare occurrence with those.

 

If it's wired devices also, again on a different VLAN, then I'd say a potential switching problem. I don't know anything about Zyxel switches, so no idea what level of management you have on them.

 

Basics of course are to reboot switches out of hours to see if it clears the issue.

[supra21]

We had a report of a desktop PC with this issue this morning. I pinged our core switch and responses were <1ms, I then did a continuous ping to the smoothwall box and response times were all over the place sometimes dropping out. We then gave it a new IP from the same range/vlan and internet speed and ping responses were normal again. So does seem to be a switch issue.

[Davit2005]

We had a report of a desktop PC with this issue this morning. I pinged our core switch and responses were <1ms, I then did a continuous ping to the smoothwall box and response times were all over the place sometimes dropping out. We then gave it a new IP from the same range/vlan and internet speed and ping responses were normal again. So does seem to be a switch issue.

 

Have you logged a call with Smoothwall about this at all. As you can ping core switch it looks like issue is not there to me.

[supra21]

Yeah I spoke to Smoothwall a while back and they suggested it was an issue at my end. I just find it odd that just changing the IP makes the ping responses and internet speeds return to normal, no changes to pc, cable, switch, port.

[Davit2005]

Yeah I spoke to Smoothwall a while back and they suggested it was an issue at my end. I just find it odd that just changing the IP makes the ping responses and internet speeds return to normal, no changes to pc, cable, switch, port.

 

Suggest raising again with them with the new found info i.e. pinging core switch pinging Smoothwall etc. just to see if this can narrow problem down. Check on the core switch logs for any issues on connectivity between the core and smoothwall.

Edited April 20, 2021 by Davit2005

[robyholmes]

Ping a device on another VLAN if you can next time. See if you get the same result as pinging the Smoothwall.