Diameter : In what scenarios following AVPs are added in a Diameter based message ?

Question

Few Diameter messages carries
- Destination-Host
- Destination-Realm only
- both Destination-Host and Destination-Realm
- Or none of both
I want to know what to use when.

Answer 1

Excluding some Diameter base requests, Destination-Realm is mandatory in all Diameter requests. Request forwarding is done based on it along with Application-Id. In some cases (typically server-initiated requests like Re-Auth request in Gx), Destination-Host is also mandatory.

In some cases, client application may want to send a request to a particular server. One example: if you want to load balance the on-line charging servers (OCS) when using Gy. You may want to partition based on say, range of mobile numbers or IP addresses of the request originator. If you specify the Destination-Host, request will be delivered only to that server, otherwise Diameter forwarding (look up based on Dest-Realm and app-id, but most implementations support more sophisticated algorithms).

Server initiated requests typically need to fill in the Destination-Host (even if it is not mandatory) because there would be many clients. But if requests are sent over an established session, Diameter nodes can figure out the recipient.

Answers are sent back the requester along the same that that request traversed, so you don't find these AVPs in answers.

Answer 2

Hi Harshita,

From RFC-6733 section 6.1 depict the following conditions when we can use Destination-Host and Destination- Realm:
1. A request that is not able to be proxied (such as a CER) MUST NOT contain either Destination-Realm or Destination-Host AVPs.
2. A request that needs to be sent to a home server serving a specific realm, but not to a specific server (such as the first request of a series of round trips), MUST contain a Destination- Realm AVP but MUST NOT contain a Destination-Host AVP. ForDiameter clients, the value of the Destination-Realm AVP MAY be extracted from the User-Name AVP, or other methods.

3.A request that needs to be sent to a specific home server among those serving a given realm MUST contain both the Destination-Realm and Destination-Host AVPs.

Thanks

Answer 3

One example of specific servers like in the above example is the Redirect DRA where Destination-Host AVP is mandatory in the request message.

Regards,
Peeyush Sharma