DNS in Evolved Packet Core (EPC)

Lately the DNS topic was addressed here, I'm happy to get back to you with more on this.
Hope you will find more detailed description of usage of DNS in EPC. The below is detailed description of, I think, most important from the DNS topic with examples of dns zone files.

UPDATE: For more info on how the EPC uses the DNS please refer to DNS in LTE label.

Home Network Domain

The Home network Domain will be in the form ‘epc.mnc<mnc-val>.mcc<mcc-val>.3gppnetwork.org’

Both <mnc-val> and <mcc-val> are 3 digits long. If the MNC of the PLM is 2 digits, then a zero shall be added at the beginning.
The Home network domain for some example Operator will be:

epc.mnc456.mcc123.3gppnetworks.org

The Home Network Domain name of an IMSI can be derived by taking the first 5 or 6 digits (depending on whether a 2 or 3 digit mnc is used), use the MNC and MNC values derived to form the domain name, add the label epc at the beginning of the domain name.
For example an IMSI 1234560123456789 has an MSIN 0123456789 and a Home network domain name of epc.mnc456.mcc123.3gppnetworks.org.

Fig. 1. DNS subdomains in EPC

The below example shows how the APN-FQDN is formed:

APN FQDN = internet.apn.epc.mnc015.mcc234.3gppnetwork.org

which consists of:

• APN Network Identifier (APN-NI) - Basically it's the APN name, from UE point of view.

APN-NI = internet

• APN Operator Identifier (APN-OI) - levels equal and below to APN level from DNS configuration point of view
  Or just the rest what is left from APN-FQDN when you remove the APN (-NI) from it.

APN-OI = .apn.epc.mnc015.mcc234.3gppnetwork.

• APN Network Identifier (APN-NI) - Basiclly it's the APN name, from UE point of view.

APN-NI = internet

Whenever configuring the DNS, no matter if this is the one you will used by any Operator in EPC deployment you are doing or just for yourself, dont forget the dots "." they are freaking important.