Need some advice as I’ve only barely used EPM. I have about 20 VVX 500s in a heavily restricted network. Almost no external connections to the internet. Phones are provisioned and working well. Intermittently, we have network outages and completely lose local DNS. I would like to have these phones setup such that they can still reach the PBX and make and receive calls. All hosts have static IPs (phones and PBX). On the Endpoint Manager Global config, I have set INTERNAL to the PBX IP and push that change across all phones. When I take out DNS on a test phone, and restart it, it never connects to the PBX. Any ideas on what I should be tweaking/configuring?
I don’t use EPM, so can’t speak to that. But a few questions:
- When you lose local DNS, I assume you mean internal DNS, correct? What is your DNS server? If it’s Microsoft Active Directory DNS and you only have a single internal DNS server, might be a good idea to deploy an additional AD DNS server. This is the root cause of the concern, after all, and in the big picture needs remedy. Beyond just phone operations.
- What does a problem Polycom desk phone look like, in terms of its configuration paging through the phone display? Any references to host names in there at all, or are all references just IP addresses?
- Perhaps EPM communicates out to Sangoma as part of its operation. Like I said, I don’t use this module. So not sure if the desk phone just communicates with FreePBX for EPM, and EPM on FreePBX is the only element communicating with Sangoma.
Are the phones on Chan-Sip or PJSip?
What does that have to do with DNS?
Are you replying to me?
PJSIP although I’m not sure how that would come into play here
Yes. This is about a DNS problem not a channel driver problem.
Yes internal DNS. Not sure if it’s Microsoft AD but I think it could be. Phones are at very remote locations so we would want that remote location to still be able to make ext-ext calls in the event of a DNS outage
Right but the OP is using IPs not FQDNs in the testing.
Is the phone on the same local network? Is it remote? Do you see the attempts hit the PBX?
Same local network. All hosts on the local network have static IPs. When we simulate a DNS outage and reboot the phone, it boots back up, displays a message about date and time out of sync, and never registers to the PBX
Did you actually run any captures or debugs to see if the phone attempted to hit the PBX? And yes, the time/date will be off if it’s not getting it from DHCP but the default NTP server on the phone which will be a FQDN. So no DNS servers set on the phone means the NTP server can’t be resolved.
Have you run any captures at the network level to see if the phone is trying to get to the IP address at all?
Wireshark did not capture any traffic from the phone to the PBX.
Let’s expand on that post. Chan_sip had known DNS limitations and those limitations are one how chan_sip resolves DNS. For example, chan_sip only does DNS lookups at startup or reload of the chan_sip driver. Meaning if the FQDN host being used by a chan_sip peer is actually a DynDNS domain, when the IP changes chan_sip won’t do a fresh DNS lookup on the FQDN. It will still think the IP is the old IP until chan_sip is restarted/reloaded forcing it to do another DNS lookup.
Chan_sip also had bad SRV support as it never looked beyond the first SRV record, so again, if an IP went down and the SRV record was serving a different IP chan_sip wouldn’t get it and continue to try the down IP.
You’re conflating how chan_sip does DNS lookups with the phone doing a DNS lookup. They are not the same thing.
1 Like
What do the phone logs say?
This is the crux of the matter. I’d assume that local DNS forwards on requests to public DNS, so other than an Internet connection being totally down, this is about a worst-case anyway. I’d suggest first pursue getting some redundancy in place in terms of DNS. As well as Internet connectvity, if it flakes out unacceptably too often.
Figure if the FreePBX connects to third-party SIP trunking, usually that involves DNS as well. Unless the provider guarantees connectivity via always up-to-date static IP on their end. If phones can get a good NTP source and register with the FreePBX without DNS, even then the SIP trunking might fall down.
I will look at those again when I access the network later today
This is a completely isolated network. The only time we would ever touch the internet would be to install a module or apply some PBX updates
How do the calls get in and out of the site in terms of PSTN connectivity? TDM like PRI, SIP trunking, etc.?