Orbi WiFi 7 RBE973
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RBR 750 dropping internet after lease expires, every 2-ish hours

osmall
Aspirant

RBR 750 dropping internet after lease expires, every 2-ish hours

I have an RBR750 (and two satellites that are currently disconnected to help with diagnostics) on xfinity.  Prior to this event, everything had been working fine with no drops for about a year.  We recently had work done in the neighborhood, which caused a 2-hour outage.  After this, my DHCP lease is only 2 hours long, and at the end of it, the internet stops working.  On the advanced -> connection status page, it looks like the lease has been renewed (with the same IP) after that 2-hour window, but the internet connectivity isn't there until I manually power cycle the modem.  If I catch it about 30 min prior to expiration, and do a release/renew (on the advanced->connection status page) it will continue functioning.  Doing just a renew (even if it appears to work by extending the time) immediately kills the internet as well.

 

I have tried replacing the modem (initially had a Docsis 3.0 Arris Surfboard, now a Docsis 3.1 Arris).  I have tried different routers.  One old router (linksys 1900 ACS) maintained a connection overnight, but this was before I realized it was related to DHCP leases, and I can't get it to replicate its success.  The linksys router was also previously used with xfinity, so my assumption is that it was recognized and got a longer lease.

 

Although I doubt this matters, while doing MRT ping/traceroute testing, I noticed that during the period when the linksys router was maintaining a connection, it's private IP (192.168.1.1) resolved to a comcast address personalcomputer.hsc1.comcast.wa or some such.  Any other time, it doesn't resolve to a name on traceroute testing.  I took this to mean that the comcast DNS server recognized the computer and had a long term lease for it, but I'm not a network professional.

 

Some version of this problem appears to have existed for a year or two now, but I haven't been able to find any suggestions to help.  The only person who seemed to have an effective strategy ended up downgrading their firmware.

Message 1 of 17

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FURRYe38
Guru

Re: RBR 750 dropping internet after lease expires, every 2-ish hours

Message 6 of 17

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FURRYe38
Guru

Re: RBR 750 dropping internet after lease expires, every 2-ish hours

What Firmware version is currently loaded?
What is the Mfr and model# of the Internet Service Providers modem/ONT the NG router is connected too?

Message 2 of 17
osmall
Aspirant

Re: RBR 750 dropping internet after lease expires, every 2-ish hours

Service Is Xfinity

Router model: RBR750

Firmware: V4.6.5.14_2.0.54

 

Modem: Arris Surfboard: SB8200 (personally owned, not provided by ISP.  But registered and functioning)

Message 3 of 17
FURRYe38
Guru

Re: RBR 750 dropping internet after lease expires, every 2-ish hours

Does the RBR show a front PINK led when this happens? 

Has a factory reset and setup from scratch been performed since last update? 

What is the CAT# LAN cable between the modem and RBR? CAT6 is recommended. 

Message 4 of 17
osmall
Aspirant

Re: RBR 750 dropping internet after lease expires, every 2-ish hours

The RBR does not show a pink light.  On the home status page, internet says waiting.  I just did a full factory reset and setup from scratch.  It was connected with a 5E, but I made a new Cat 6.

 

Other updates: 

 

I was able to get my Linksys 1900 ACS router to work just fine, accept renewals etc.  No major changes, just started working.

The Orbi still loses internet connectivity at the end of the lease, or whenever I try to renew.  I can now use release/renew (on connection status) to get internet to work without power cycling the modem.

 

 

 

Message 5 of 17
FURRYe38
Guru

Re: RBR 750 dropping internet after lease expires, every 2-ish hours

Message 6 of 17
CrimpOn
Guru

Re: RBR 750 dropping internet after lease expires, every 2-ish hours

I have always wondered how the Orbi products handle DHCP assignments from the ISP.   There is an option on the Orbi debug page to "Enable LAN/WAN Packet Capture". When the debug information is saved to the user's computer, the zip file includes two pcap files (lan.pcap and wan.pcap).  Opening the wan.pcap file with Wireshark and setting a display filter to 'dhcp' (lower case) will show the conversation between Orbi and ISP.

 

(I have wanted to capture this conversation on my Spectrum account for a long time, however Spectrum gives me a 1 Day lease (86,400 seconds) and the debug buffer will not hold that much data.)  With your 2 hour lease, it should be possible to capture what is going on.

Message 7 of 17
FURRYe38
Guru

Re: RBR 750 dropping internet after lease expires, every 2-ish hours

I would also check the RBRs debug page for system uptime when this happens as well. 

 

Possible that there maybe a odd ISP service handling issue between the modem and RBR. I've ran my 7 series online and haven't seen this though I don't have the users same cable modem or ISP service. 

Message 8 of 17
osmall
Aspirant

Re: RBR 750 dropping internet after lease expires, every 2-ish hours

I've updated firmware, found the debug page, started capture.  I'll save traffic, should have an answer in about an hour.

Message 9 of 17
CrimpOn
Guru

Re: RBR 750 dropping internet after lease expires, every 2-ish hours

Thanks.  The way I understand DHCP, what is supposed to happen is the device that has been granted an IP lease is supposed to wait untii the lease is 50% expired and attempt to renew it, at increasingly short intervals, until the lease finally expires.

https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol 

In this case, a 2-hour lease would imply that there should be DHCP packets going both directions at approximately one hour.

 

Will be interesting to see what happens.

Message 10 of 17
osmall
Aspirant

Re: RBR 750 dropping internet after lease expires, every 2-ish hours

After the firmware update, it seems like it survived one lease transition.  Here's the log.

 

Message 11 of 17
FURRYe38
Guru

Re: RBR 750 dropping internet after lease expires, every 2-ish hours

I would ask your ISP why they are changing the WAN IP so much. Two hours seems to often for WAN IP address change. My ISP goes for days or months unless I reboot my modem. 

Message 12 of 17
CrimpOn
Guru

Re: RBR 750 dropping internet after lease expires, every 2-ish hours


@osmall wrote:

After the firmware update, it seems like it survived one lease transition.  Here's the log.


Great work, thanks.  This give the impression that the Orbi is following RFC2131 (DHCP) to the letter:

 DHCP clients are allocated leases that last for some period of time. Clients begin to attempt to renew their leases once half the lease interval has expired.[11]: Section 4.4.5 Paragraph 3  They do this by sending a unicast DHCPREQUEST message to the DHCP server that granted the original lease. If that server is down or unreachable, it will fail to respond to the DHCPREQUEST. However, in that case the client repeats the DHCPREQUEST from time to time,[11]: Section 4.4.5 Paragraph 8 [b] so if the DHCP server comes back up or becomes reachable again, the DHCP client will succeed in contacting it and renew the lease.

If the DHCP server is unreachable for an extended period of time,[11]: Section 4.4.5 Paragraph 5  the DHCP client will attempt to rebind, by broadcasting its DHCPREQUEST rather than unicasting it. Because it is broadcast, the DHCPREQUEST message will reach all available DHCP servers. If some other DHCP server is able to renew the lease, it will do so at this time. 

This is from the Wikipedia section under Reliability.

 

If you do happen to call Xfinity support (for entertainment, perhaps), in addition to asking how long the 2-hour IP lease is going to continue (and why), it would be fun to offer to send this Wireshark log to their "Tier 2" support to illustrate how Xfininity is not following internet standards.

 

DHCP requests are UDP packets, which means there is no guaranteed delivery (as with a TCP session that has been opened). It is entirely possible for a DHCP request to "go missing", or for a DHCP server to get overloaded and fail to respond.  That is why the standard is to make multiple attempts.  If the log had covered the full two hours, I would expect to see a request at 12 hours, 18 hours, 21 hours, etc. down to the point where they were just seconds apart as in the capture.

Message 13 of 17
Hvaldes
Aspirant

Re: RBR 750 dropping internet after lease expires, every 2-ish hours

I'm also having the same issue.   Any updates?

Message 14 of 17
osmall
Aspirant

Re: RBR 750 dropping internet after lease expires, every 2-ish hours

For me, it was fixed by updating to a slightly newer firmware.  However, even though it's currently working, I am still only getting 1-2 hour DHCP leases.  The DHCP server does not respond unless the router broadcasts the request.  It doesn't respond to direct requests apparently?  Maybe Xfinity is misconfiguring it's packets and it's telling me to contact the wrong DHCP server or it's on another subnet? 

Message 15 of 17
Hvaldes
Aspirant

Re: RBR 750 dropping internet after lease expires, every 2-ish hours

Alright. I'll be contacting Xfinity. I'll update you if it changes anything on my end. I'm up to date on firmware, but have same exact issue you do.
Message 16 of 17
Hvaldes
Aspirant

Re: RBR 750 dropping internet after lease expires, every 2-ish hours

Contacted Xfinity. Got redirected to Netgear...didnt get much help. But I changed my router settings from Dynamic to Static.. seems to have worked. No more lease time.

Message 17 of 17
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