"503 Service Unavailable" message for phones registered on Publisher

[00u1c1e8sgNfbgbZ15d7]

Hello everyone.

My customer has a CUCM ver 12.5.1.11900-146 cluster with one PUB & one SUB servers

They have one SIP trunk to PSTN and another to a internal Dispatch service (TK_dp).

To call to dispatch services they can use internal RP: 34.50.

To get access to this RP from PSTN they can call DID 787-2063450.

The same CSSs are used for phones registered on PUB & SUB.

All phones (registered on PUB & SUB) can call each other internally, and call PSTN with no issue.

DB replication is OK on cluster.

All phones registered on SUB can call dispatch internal RP 34.50 with no issue (using TK_dp) . they also can call dispatch calling PSTN DID 787-2063450.

All phones registered on PUB can call dispatch service calling PSTN DID 787-2063450.

No phone registered on PUB is able to call internal dispatch RP 34.50, they get "503 Service Unavailable" from CUCM PUB, administrators from Dispatch system confirmed they never receive call attempts from phones registered on PUB.

On SIP traces "503 Service Unavailable" are coming from PUB to phones just after "100 trying" message.

Any help to figure out root cause of this problem will be welcomed.

THANKS

[Roger Kallberg]

Is this a new problem, has it ever worked and now it doesn’t? If so what has changed to cause it to break?

As a first step you can check if the SIP trunk is set to run on all nodes and also the same for the route list. Also check if the receiving end is setup to accept calls from both IPs, ie accept invites from either Sub or Pub. It is quite common for systems to not allow traffic from unknown sources, for example CM does not allow that, it only allows traffic from known sources and it knows that by the IP(s) put on the trunks.

[00u1c1e8sgNfbgbZ15d7]

Roger thanks for comment,

I will check this TK & RL option.

Regarding other comment, I asked them that, but they insist they do not receive any traffic from PUB servers, and when I check SIP flows the "503 Service Unavailable" message is generated by PUB to IP Phone

Thanks

[Roger Kallberg]

Never trust what anyone tells you for a system that you're not able to look at yourself. I would do a packet capture on the pub to see if it is actually sending any traffic to the other end. If you don't know how to do a packet capture in CVOS have a look at this document.

[00u1c1e8sgNfbgbZ15d7]

Roger, i changed setting on SIP trunk to run on all nodes.

I also reset SIP trunk, but still phones registered on PUB server can not call Dispatch internal RP: 34.50.

I sent another email to Dispatch administrators asking if:

a) Their SIP TK is pointing to both PUB & SUB

b) Confirm if both PUB & SUB are authorized ( if any trust list is applied)

Thanks

[00u1c1e8sgNfbgbZ15d7]

We got answer from Dispatch system administrators.

They said they said:

a) They get send options requests to both PUIB & SUB from their router.

b) They get 200 OK responses from both PUB & SUB

c) They do not get  phone calls through PUB,  and they do not show up in their SIP captures.

As I said before, on our traces we only see "503 Service Unavailable" message from PUB to phones, we do not see the leg from TK_dp destination IP address.

IP Phone <--> PUB

When we take the traces of calls from phones registered on SUB, we can see both legs

IP phone <--> SUB <--> TK_dp dest IP

[Roger Kallberg]

Have you done the packet capture that I suggested?

[00u1c1e8sgNfbgbZ15d7]

Yes  i did it

For reference:

a) PUB: 172.16.30.10

b) Registered IP phone on PUB: 172.16.20.223.

c) Customer was calling from ext 4665 to another affected RPs 4720 & 5720

You will see that we are getting on "503 Service Unavailable" message Reason Code Q.850 cause 41 ( temporary Failure).

I am validating Media Resources associated to this phone Device pool

I appreciate your help

[00u1c1e8sgNfbgbZ15d7]

Something additional I confirmed today CUCM PUB, problems with calls from phones registered on PUB started when this server was rebooted for a power outage.

I checked services today and all are OK.

I also confirmed phones all phones (registered on both servers) are using the same MRGL

[00u1c1e8sgNfbgbZ15d7]

Hello I also confirmed on pcap files that external server ( destination of dispatch trunk) is receiving SIP Options messages from my affected CUCM PUB, so this CUCM PUB is not blocked on their site.

And internally ANYTIME I tried to call affected RP 4720 or 5720 I got "503 Service Unavailable" message Reason Code Q.850 cause 41 ( temporary Failure).

Any help will be welcome