6.1.8. Redirecting Requests
6.1.8. Redirecting Requests
When a redirect agent receives a request whose routing entry is set to REDIRECT, it MUST reply with an answer message with the 'E' bit set, while maintaining the Hop-by-Hop Identifier in the header, and include the Result-Code AVP to DIAMETER_REDIRECT_INDICATION. Each of the servers associated with the routing entry are added in a separate Redirect-Host AVP.
+------------------+
| Diameter |
| Redirect Agent |
+------------------+
^ | 2. command + 'E' bit
1. Request | | Result-Code =
[email protected] | | DIAMETER_REDIRECT_INDICATION +
| | Redirect-Host AVP(s)
| v
+-------------+ 3. Request +-------------+
| example.com |------------->| example.net |
| Relay | | Diameter |
| Agent |<-------------| Server |
+-------------+ 4. Answer +-------------+
Figure 5: Diameter Redirect Agent
The receiver of an answer message with the 'E' bit set and the Result-Code AVP set to DIAMETER_REDIRECT_INDICATION uses the Hop-by-Hop Identifier in the Diameter header to identify the request in the pending message queue (see Section 5.5.4) that is to be redirected. If no transport connection exists with the new peer, one is created, and the request is sent directly to it.
Multiple Redirect-Host AVPs are allowed. The receiver of the answer message with the 'E' bit set selects exactly one of these hosts as the destination of the redirected message.
When the Redirect-Host-Usage AVP included in the answer message has a non-zero value, a route entry for the redirect indications is created and cached by the receiver. The redirect usage for such a route entry is set by the value of Redirect-Host-Usage AVP and the lifetime of the cached route entry is set by Redirect-Max-Cache-Time AVP value.
It is possible that multiple redirect indications can create multiple cached route entries differing only in their redirect usage and the peer to forward messages to. As an example, two(2) route entries that are created by two(2) redirect indications results in two(2) cached routes for the same realm and Application Id. However, one has a redirect usage of ALL_SESSION, where matching requests will be forwarded to one peer; the other has a redirect usage of ALL_REALM, where request are forwarded to another peer. Therefore, an incoming request that matches the realm and Application Id of both routes will need additional resolution. In such a case, a routing precedence rule MUST be used against the redirect usage value to resolve the contention. The precedence rule can be found in Section 6.13.