?? Deep Dive into Packet Core Telecom: The Role of DNS in User Plane Node Selection! ??

What is DNS?

In telecom networks, when nodes like SGW-U and PGW-U are deployed, specific details such as TAC (Tracking Area Code) and APN (Access Point Name) are preconfigured in the DNS. This configuration ensures that the network knows which SGW to connect for a given TAC and which PGW to connect for a given APN. SGW-C queries the DNS using TAC details, while PGW-C queries DNS using APN information. DNS should be configured with TAC/APN details for services like x-3gpp-@@@:x-sxa for SGW-U selection and x-3gpp-@@@:x-sxb for PGW-U selection.

DNS Cache in Control Plane

SGW-C and PGW-C (Control plane) query DNS, and the information is stored locally in the DNS cache of the control plane. This cached information remains for the configured time (TTL).

Will Control Plane Node Contact DNS for Every Attach?

No, as long as the information is available in the cache, the control plane node will not contact DNS for resolving queries.

What Happens if DNS is Not Working?

Even if DNS is not working, the user plane node will be selected based on the cache information. If the cache is cleared, then the user plane will be selected based on the local configuration in the control plane node.

What Happens When DNS Configuration Changes?

No impact as long as the cache information is alive.

Can Cache Information Be Cleared Manually?

Yes, after every change in DNS, it is advisable to clear the local DNS cache.

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