No S7 routing with CP 300/400 < V3 as router
With S7 routing between S7‑1200 or S7‑1500 stations, no connection is established when older S7‑300/400 CPs are connected in between as routers. The following types of communication that run over ISO transport or ISO-on-TCP connections are affected:
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S7 communication
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PG communication
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HMI communication
The behavior applies to S7‑300/400 CPs with a firmware version < V3.0 for which the TSAP length is limited to 2 bytes.
In contrast, like the S7‑1200/1500, S7‑300/400 CPs as of V3.0 support long TSAPs and thus also S7 routing.