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authorAnders Svensson <[email protected]>2015-08-24 16:14:49 +0200
committerAnders Svensson <[email protected]>2015-08-25 00:03:03 +0200
commit502189ba42469d3332bc0658caa2bd0de1e3fcb9 (patch)
tree0099a98bd0d934766809085056fb1e2022b52790 /lib/diameter/doc
parent155c22ff3ce3f667d4a984bd6648f029e0998381 (diff)
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Add service_opt() strict_mbit
There are differing opinions on whether or not reception of an arbitrary AVP setting the M-bit is an error. 1.3.4 of RFC 6733 says this about how an existing Diameter application may be modified: o The M-bit allows the sender to indicate to the receiver whether or not understanding the semantics of an AVP and its content is mandatory. If the M-bit is set by the sender and the receiver does not understand the AVP or the values carried within that AVP, then a failure is generated (see Section 7). It is the decision of the protocol designer when to develop a new Diameter application rather than extending Diameter in other ways. However, a new Diameter application MUST be created when one or more of the following criteria are met: M-bit Setting An AVP with the M-bit in the MUST column of the AVP flag table is added to an existing Command/Application. An AVP with the M-bit in the MAY column of the AVP flag table is added to an existing Command/Application. The point here is presumably interoperability: that the command grammar should specify explicitly what mandatory AVPs much be understood, and that anything more is an error. On the other hand, 3.2 says thus about command grammars: avp-name = avp-spec / "AVP" ; The string "AVP" stands for *any* arbitrary AVP ; Name, not otherwise listed in that Command Code ; definition. The inclusion of this string ; is recommended for all CCFs to allow for ; extensibility. This renders 1.3.4 pointless unless "*any* AVP" is qualified by "not setting the M-bit", since the sender can effectively violate 1.3.4 without this necessitating an error at the receiver. If clients add arbitrary AVPs setting the M-bit then request handling becomes more implementation-dependent. The current interpretation in diameter is strict: if a command grammar doesn't explicitly allow an AVP setting the M-bit then reception of such an AVP is regarded as an error. The strict_mbit option now allows this behaviour to be changed, false turning all responsibility for the M-bit over to the user.
Diffstat (limited to 'lib/diameter/doc')
-rw-r--r--lib/diameter/doc/src/diameter.xml43
1 files changed, 43 insertions, 0 deletions
diff --git a/lib/diameter/doc/src/diameter.xml b/lib/diameter/doc/src/diameter.xml
index 854bc5b432..b0cff32c9a 100644
--- a/lib/diameter/doc/src/diameter.xml
+++ b/lib/diameter/doc/src/diameter.xml
@@ -912,6 +912,49 @@ Options <c>monitor</c> and <c>link</c> are ignored.</p>
Defaults to the empty list.</p>
</item>
+<marker id="strict_mbit"/>
+<tag><c>{strict_mbit, boolean()}</c></tag>
+<item>
+<p>
+Whether or not to regard an AVP setting the M-bit as erroneous when
+the command grammar in question does not explicitly allow the AVP.
+If <c>true</c> then such AVPs are regarded as 5001 errors,
+DIAMETER_AVP_UNSUPPORTED.
+If <c>false</c> then the M-bit is ignored and policing
+it becomes the receiver's responsibility.</p>
+
+<p>
+Defaults to <c>true</c>.</p>
+
+<warning>
+<p>
+RFC 6733 is unclear about the semantics of the M-bit.
+One the one hand, the CCF specification in section 3.2 documents AVP
+in a command grammar as meaning <b>any</b> arbitrary AVP; on the
+other hand, 1.3.4 states that AVPs setting the M-bit cannot be added
+to an existing command: the modified command must instead be
+placed in a new Diameter application.</p>
+<p>
+The reason for the latter is presumably interoperability:
+allowing arbitrary AVPs setting the M-bit in a command makes its
+interpretation implementation-dependent, since there's no
+guarantee that all implementations will understand the same set of
+arbitrary AVPs in the context of a given command.
+However, interpreting <c>AVP</c> in a command grammar as <b>any</b>
+AVP, regardless of M-bit, renders 1.3.4 meaningless, since the receiver
+can simply ignore any AVP it thinks isn't relevant, regardless of the
+sender's intent.</p>
+<p>
+Beware of confusing mandatory in the sense of the M-bit with mandatory
+in the sense of the command grammar.
+The former is a semantic requirement: that the receiver understand the
+semantics of the AVP in the context in question.
+The latter is a syntactic requirement: whether or not the AVP must
+occur in the message in question.</p>
+</warning>
+
+</item>
+
<marker id="string_decode"/>
<tag><c>{string_decode, boolean()}</c></tag>
<item>