## 3.18.5  SAP HANA Inter-Node Communication Problems
This section contains analysis steps that can be performed to resolve SAP HANA inter-node communication issues.
## Procedure
1. If communication issues occur between different nodes within an SAP HANA scale-out environment, usually the SAP HANA tracefiles contain corresponding errors.
A typical error recorded would be:
```
 Sample Code e TrexNet Channel.cpp(00343) : ERROR: reading from channel #### <IP_of_remote_host:3xx03> failed with timeout error; timeout=60000 ms elapsed e TrexNetBuffer BufferedIO.cpp(01092) : channel #### from : read from channel failed; resetting buffer
```
To understand those errors it is necessary to understand which communication parties are affected by this issue. The &lt;IP:port>= information from the above mentioned error already contains valuable information. The following shows the port numbers and the corresponding services which are listening on those ports:
Interpreting the above error message it is safe to assume that the affected service was failing to communicate with the indexserver of one node in the scale-out system. Please note that these errors are usually caused by network problems and should be analyzed by the person responsible for OS or network or the network team of the hardware vendor.
2. In SAP HANA cockpit go to the Threads tile and check the column Thread Status for Network Poll, Network Read, Network Write.
In case the Threads tile in the SAP HANA cockpit shows many threads with the state Network Poll, Network Read or Network Write, this is a first indication that the communication (Network I/O) between the SAP HANA services or nodes is not performing well and a more detailed analysis of the possible root causes is necessary. For more information about SAP HANA threads, see SAP KBA 2114710 - FAQ: SAP HANA Threads and Thread Samples .
3. Run SQL: "HANA_Network_Statistics".
As of SAP HANA SPS 10 the view m_HOST_NETWORK_STATISTICS provides SAP HANA host related network figures. The SAP HANA SQL statement collection from SAP Note 1969700 - SQL Statement Collection for SAP HANA contains SQL: 'HANA_Network_Statistics' which can be used to analyze the network traffic between all nodes within a SAP HANA scale-out system.
For a detailed documentation of the figures from this output, please refer to the documentation section of the SQL statement SQL: 'HANA_Network_Statistics' .
4. Run SAP HANA Configuration Mini Checks from SAP KBA 1999993 - How-To: Interpreting SAP HANA Mini Check Results .
The "Network" section of the mini-check results contains the following checks:
```
| 1520|Retransmitted TCP segments (%)           |       |0.00571   |<= 0.10000    | | 2222200| | 1522|Bad TCP segments (%)                     |       |0.00017   |<= 0.01000    | | 2222200| ----------------------------------------------------------------------------------------------
```
The results usually contain an "expected value" (which provides a certain "rule of thumb" value) and a "value" field which represents the actual value recorded on the system. If the recorded value is breaching the limitations defined by the expected value, the "C" column should be flagged with an 'X'. You can then check the note for this item referenced in the column SAP_NOTE.
## Related Information
```
SAP Note 2114710 SAP Note 1969700 SAP Note 1999993
```