Remote office phones not working in office with more than one phone

[scottyg]

I'm trying to resolve a problem for a client that has a Mitel 5000 PBX with 8662e phones.
Every remote site except for one, has a single phone. The other remote office has two remote phones, and this is the site that is not working properly.
There are some instances of one-way audio, which obviously points to a NAT/firewall problem, but I have literally scoured these forums and others, and no answer has resolved the issue.
Examples of relevant-looking posts that have not helped:
http://mitelforums.com/forum/index.php?topic=4031.0
http://mitelforums.com/forum/index.php?topic=3932.0
http://mitelforums.com/forum/index.php?topic=4679.0

SO, here's the scenario.
Mitel 5000 PBX with a public static IP that is 1:1 NAT'd to the PBX's internal IP.  To me, this takes NAT right out of the picture, at least on the 5000's end of things.

The remote office is on Comcast Business Class, with a Netgear modem.  The location also has a Sonicwall, but the phones are plugged directly into the cable modem, whose firewall rules are disabled.  It's in Residential Gateway mode, if that makes a difference.
The phones used to have this info:

Code: [Select]

static ip: 192.168.200.201
subnet mask: 255.255.255.0
gateway: 0.0.0.0
DHCP: enabled
Remote UDP port: 5567
Remote TCP port: 5566
Remote IPC IP address: (public IP of PBX)
TFTP address: 192.168.200.201
Since the sites are not connected via VPN, I changed the phones to the following (these are just the differences):

Code: [Select]

static ip: 10.5.10.200  (existing subnet on the comcast modem)
getway: 10.5.10.1
DHCP: disabled
TFTP: (public IP of PBX)
This literally made no difference. Both phones still partially work, and they have the same issues as before.

So what exactly are the issues?
Well, there are some specific cases of one-way audio, but really, we can tell that they are still broken by the following:
Call from a cell phone.  Answer with Phone A.  Place call on hold.  Phone A's red light is now blinking, indicating hold.  Go to Phone B, and the light is steady, so you can't pick up the line to transfer.

What seems to be happening is that there are two phones in the office, so the routing of the calls gets confused.  This remote office had no issues before they installed the second line.

Is this configuration even possible?  There is no MBG or Teleworker involved -- just the remote phones.
Can two phones exist in the same remote office in this scenario?  For their other remote offices, it is as simple as port forwarding the proper ports to the phone's ip address, but here, there are two phones, so I'm not clear on how the routing would work. This is assuming this even needs to be done in the first place, because as far as I know, I shouldn't have to port forward anything.

Sorry if this was long-winded. I'm sure I left out some important details, but let me know and I'll fill in the blanks.  Thanks for any help!

[Tech Electronics]

Scottyg,

I am not so sure your test is valid for your problem. Are you able to reverse transfer the call from phone A to phone B when the call is on hold? To do this use the reverse transfer feature, default FAC us 4, so you would need to dial 4+A's extension number to get the call.

Now, as for your one-way audio issue is this a consistent problem and in what scenarios can you recreate it?

Thanks,

TE

[619Tech]

The 1:1 NAT jumps out at me because I’ve had countless failures when network admin try this config. I always go with port forwarding of needed ports. That being said, you have multiple sites connected without issue, so we will skip the near-end (5000/HX) side. I’m not sure how you are plugging in multiple endpoints into a cable modem. I’ve plugged in a PC directly before, but never had success with multiple devices. Normally, you would have a router behind the cable modem, providing DHCP to the endpoint’s subnet. The endpoints have the HX public IP set as their ICP & TFTP (or use Teleworker), but pull local addressing from the router. The ISP has the MAC/IP of the modem, and can route traffic to/from it. The ISP does not know about the endpoints you have static addressed on the 10.5.10.0 subnet, and I think that’s your problem.

[scottyg]

@Tech Electronics:
I'm going to the client's office today to do these tests in person (up till now, the remote users have been telling me the symptoms as the occur, so I can't vouch for the absolute validity of these symptoms).
I'll post a follow up in a bit.

@619Tech:
I've heard similar "horror stories" about trying to successfully use 1:1 NAT. On the other hand, yes, all the other remote sites work without issue, so I have to assume the 1:1 NAT is working.  Note that all of this setup was done by someone other than me; a person whose technical know-how in networking is not perhaps best suited for this :-)  I am actually debating changing their 1:1 NAT to being only port forwarded simply for security reasons, but I don't want to another variable to the equation at the moment.

Anyway, at the remote site, the multiple endpoints are plugged directly into the modem, which has four ports, and has a private internal subnet of 10.5.10.0/24. I'm wondering if this modem is problematic, because obviously, it has to do some kind of NAT in order to translate addresses from the private to public interface.  There are, however, no settings for configuring this NAT. This may be what others were referring to when they say the Comcast's modems are problematic when using them as the gateway/router with ip phones.

Let me ask you this: In theory, in my scenario, with two properly configured endpoints (without Teleworker / MGB), should I be able to plug both phones into a router and have them function properly side by side?  I have to believe the answer is yes, but the part that is confusing me, is that one of the other remote sites only has a single phone, and he was having trouble until he port forwarded the appropriate ports on his end, to the ip address of his Mitel phone.  I can't vouch for his statement, since I didn't see his config, but if that were true, how would one apply that to an office with TWO endpoints?
(I think the answer is that port forwarding simply does not really need to be done on the endpoint side of things.  The firewall does, however, need to allow outgoing traffic on the necessary ports. )

[Rasritz]

@scottyg:


I'm just curious if you ever resolved this issue and what the solution was?

[NTEDave]

Hello

I have remote offices with multiple phones set up and they work fine, the only difference is they are 53xx series phones.

As above we use port forwarding and open ports rather than 1 to 1 NAT for remote handsets.