CER and IP Subnets

[PNI-ITRNP]

I’m thinking this should be easy for someone to explain, what if anything, could happen here. I have a remote site connected to the Home Office via VPN. The phones at this remote site connect over this site-to-site VPN.

Now, when they call 911, they go out the main office PRI, this all works great. However, because this is a remote VPN site, I want to make use of ERL’s dynamic. Meaning, if a phone is changed out because of whatever reason, or a new phone is added to the remote site I don’t want to have to manually configure the phone in CER as I am doing now.

I would like to make use of IP Subnets, but I believe I need to enable “Use IP Address from call signaling”. If so, would that have any effect on CER working with phones identified on Switch Ports?

Currently, we have Switch Ports configured and if a call comes through a Switch Port that will define what ERL is used. For the VPN Sites, I manually configured the phones in CER and assigned the ERL to use. But again, if I can make it dynamic for a VPN site through the use of IP Subnets that would be excellent.

I want to enable the setting, but not sure if that will cause any issues with the current setup or not.

If anyone has experience in this area, I would love some advice!

[Maren Mahoney]

The “Use IP Address from call signaling” setting is configured on CER if you want CER to determine the location of a phone at the time the 911 call is placed, based on the IP address of the phone at that moment.

If you are simply setting up an ERL based on IP Subnet, then configure the subnet and you are done. You do not need that checkbox in addition to configuring the IP Subnet itself.

Maren

[PNI-ITRNP]

That is correct it is set in CER.

I did create an IP Subnet, removed the manually configured phone I had, and tested the 911 call and it did not work.

CER used the default ERL rather than the one I configured for the remote VPN IP Subnet!

My thinking was that based on this Note I found in Cisco Emergency Responder Release Notes, it leads me to believe I need to enable the setting:

“Any IP endpoint can be tracked at call time using the IP subnet provided that the Use IP Address from Call Signaling Telephony setting is enabled. “

[Maren Mahoney]

That's referring to any IP telephony device that CUCM manages to get to talk to CER. Phones registered to CUCM in a particular subnet have that information exchanged with CER via SNMP, which causes a phone to be in an IP Subnet.

First: For the phones that are at the remote site via VPN - what IP subnet are the registered with? Is that the subnet you have defined in CER? (Probably, just double-checking...)

Second, If the subnet is defined correctly and the remote phones are registered to CUCM, then when you go into the IP Subnet listing in CER there is a link/button for "Phones" or "Member Phones" or some such thing. (I don't have a CER in front of me at the moment.) If the remote phones are listed, then this means CER recognizes them as belonging to the subnet. So if they are mis-routed during a 911 call, then I would suspect some other problem like the route pattern in CER or something.

If the phones are registered to CUCM with a particular IP, that IP is in a subnet that is defined in CER, but the phones are not listed in CER as members then CER is not recognizing them as belonging to the subnet and we'd have to troubleshoot that.

Let us know.

Maren

[PNI-ITRNP]

Thanks, @Maren Mahoney 

Here are the answers to your questions.

First: Yes, as an example lets say the subnet is 192.168.9.0/24 that is what is configured on CER.

Second: No phones display here, it actually says “No phones has been tracked in this IP Subnet.”

If the phones are registered to CUCM with a particular IP, that IP is in a subnet that is defined in CER, but the phones are not listed in CER as members then CER is not recognizing them as belonging to the subnet and we'd have to troubleshoot that.
That seems to be the case, for now, I’m going to manually configure the phones I need to be identified. Then I will mess with another test VPN site and a phone that I have to get this working.

[PNI-ITRNP]

I Tested the CER IP Subnet with a test VPN Site I have configured.

I cannot get this to work whatsoever.

In CER I have the IP Subnet defined as 10.9.1.0 / 255.255.255.0, but after running the update no phones are tracked.

I have one phone in this Test environment that connects to CUCM over a site-to-site VPN with no issues

If I configure the phone manually in CER and perform a Test 911 it works perfectly fine. However, if I use the IP Subnet define ERL it does not assign the correct ERL and uses the default ERL.

This whole Cisco Environment is driving me crazy, especially since it was handed to me and I have no documentation from the previous admin to know what they configured, the why’s or how’s!

But that’s what makes it so much fun!!! :)

As always, everyone's advice is much appreciated!

[rikardkrvaric]

Did you ever get a resolution on this IP Subnet stuff?

We have a large switch replacement project going on for all of 2021 and 2022. I've added the new switches via SNMPv3, but SNMPv3 is apparently not working. (v1 & v2 no longer secure, or approved)

So, I figured at least, as long as I enter the IP Subnets, that should work.

I've added dozens of subnets, but phones are still showing up as "Unlocated phones".

(Importing subnets doesn't work either, so I've painstakingly added many of them manually).

Did you get the phones to get their ERL via IP Subnets?

CER: 12.5.1.23900-19

[PNI-ITRNP]

Yes, we did but we have a combination of IP Subnet and Manually configured phones. The manually configured phones were for smaller remote offices with only a few phones. These were also connected via site-to-site VPN and had their own voice gateway for 911 via a POTS line.

The other sites which were larger, we did use IP Subnet and Route Plans. Basically, once we had the Route Plan in place, we configured the ERL to use the specific Route Plan required. However, there were additional pieces because we use Comcast for our Voice Provider and they perform their own number matching for 911, so some of the configuration required a specific Transform Mask so that when the call went out the Comcast PRI it could associate the 911 call with the correct location.

This meant that even though we had ALI information in CER, it was not being used because Comcast was overriding it based on the calling number.

As far as the IP Subnet we did configure SNMPv2 for the main switches at the desired locations, and this worked for us to identify those phones at those locations using SNMPv2 and IP Subnets. If I remember correct, we definitely needed SNMPv2 to work before phones were identified using the IP Subnet. Although it has been two years since we worked on that issue.