mipv6: put the Binding Acknowledgement P flag at 0x20 - #1238

A Proxy Mobile IPv6 (PMIPv6, RFC 5213) Proxy Binding Acknowledgement carries its Proxy Registration (P) flag at 0x20 of the flags octet, as RFC 5213 Section 10 assigns it. INET wrote and read it at 0x40, the Mobile Router (R) flag of the Network Mobility (NEMO) Basic Support Protocol, RFC 3963. The encode and decode pair agreed, so simulations were unaffected; the bytes on the wire were wrong.

Closes #1237

The problem

src/inet/networklayer/mipv6/MobilityHeaderSerializer.cc:186 (serialize) and :318 (deserialize):

stream.writeByte((ba->getKeyManagementFlag() ? 0x80u : 0)
        | (ba->getProxyRegistrationFlag() ? 0x40u : 0)); // P-flag (RFC 5213)
...
ba->setProxyRegistrationFlag((kFlag & 0x40u) != 0); // P-flag (RFC 5213)

A capture of the local mobility anchor's backhaul in examples/ipv6/pmipv6, dissected by tshark:

The Proxy Binding Update was already right: P = 0x0200 in its 16-bit flags field.

In the receive direction, a NEMO Binding Acknowledgement with the R flag set was decoded as a proxy one, and the deserializer then read proxy options that a NEMO message does not carry.

Architectural surface

Packet content only: the serialized position of one flag in the Binding Acknowledgement. No C++ interface, NED parameter, message field or feature descriptor changes.

Verification

Reproduction, before and after:

cd examples/ipv6/pmipv6
inet -u Cmdenv -c General --sim-time-limit=12s \
  '--*.lma.recordPcap=true' '--*.lma.pcapRecorder[0].pcapFile="lma.pcap"' \
  '--**.fcsMode="computed"' '--**.crcMode="computed"' '--**.checksumMode="computed"'
tshark -r lma.pcap -Y mipv6

New unit test tests/unit/MobilityHeaderSerializer_1.test compares the octet with the RFC layout: a Proxy Binding Acknowledgement serializes its P flag to 0x20, a received 0x20 decodes as the P flag, and a received 0x40 does not. It fails on master and passes with the fix.

All runs use a release build (make MODE=release in the root, then make MODE=release in tests/module/lib, tests/unit/lib and tests/serializer/lib); the test commands pass --no-build. Master has no Proxy Mobile IPv6 module test, and the Mobile IPv6 module tests send no Proxy Binding Acknowledgement, so the focused evidence is the new unit test and the /examples/ipv6/pmipv6/ fingerprint row.

Suites, each run on unmodified master (49e1fa0945) and with this commit:

The commit was also built in debug mode, with make MODE=debug -j4 at the repository root, in tests/module/lib and in tests/unit/lib, exit 0, with no compiler warning in the changed file. On that build cd tests/module && inet_run_module_tests -m debug --no-build -l ERROR -f 'MIPv6|PMIPv6' passes 11 of 11, MIPv6_tcp_handover included, and cd tests/unit && inet_run_unit_tests -m debug --no-build -f MobilityHeaderSerializer_1 passes, both exit 0.

The 62 fingerprint errors are configurations whose optional features are not built (VoipStreamSender, TcpLwip, Z3GateScheduleConfigurator, the OpenSceneGraph visualizer showcases). Both failures also occur on master.

inet_run_statistical_tests -m release -w examples/ipv6/pmipv6, against statistics repository 9ab4c26a45, passes. Gates: check-commits.sh origin/master..HEAD, check-classification.sh origin/master..HEAD, check-source-seals.sh --base origin/master and check-architecture.sh src/inet/networklayer/mipv6 pass. check-naming.sh --base origin/master fails on pre-existing directory names, as on master, and finds no changed NED or MSG file. The unscoped check-architecture.sh and check-interfaces.sh fail with output identical to master's.

Fingerprints: the /examples/ipv6/pmipv6/ fingerprint that hashes packet bytes (~tND) moves from bd46-d85c to db46-aa59, because one octet of each Proxy Binding Acknowledgement changes. The fingerprint of event times, module paths, message lengths and module-supplied extra data (tplx) and the one of event times, node paths and message lengths of packets between nodes (~tNl) are unchanged. The display-string and canvas-figure fingerprint (tyf), which -F tyf skips, already fails on master: ./fingerprinttest -s -m pmipv6 examples.csv gives 05f8-fee3 against the recorded 0277-d784. This commit gives the same value, so the row is left as it is.

Not addressed here

The proxy mobility options after the fixed fields are still written back to back without option type and length octets, so Wireshark ends the dissection in a spurious option. MobilityHeaderSerializer.cc:23 declares this as a modelling simplification.