Network Loop between Client Server Network(172.16.4.xxx) and Control Network(172.16.80.xxx)
Error message from RNRP
Tools to help find problems in network configuraon, ver 4.1, src_port=2425
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0 - Quit
1 - Search own networks for nodes with configuraon or network errors
2 - Get configuraon parameters and error logs from one node
3 - Get network map from one node
4 - Change log condions in one node (for experts)
5 - Test rnrp response me from one node
6 - Find nodes with rnrp on one network
7 - Unblock interface blocked in Windows aer network loop detecon
8 - Network to node throughput test. Cauon, this may disturbe node !!!
9 - Show diagnoscs counters from one node and area
Enter your choice : 1
Used network adapters:
area= 1 CSN1 172.16.4.xxx Output: 1000 Mbit/s 0 errors, Input: 1000 Mbit/s 0 errors
area= 1 CSN2 172.17.4.xxx Output: 1000 Mbit/s 0 errors, Input: 1000 Mbit/s 0 errors
area=20 CN1 172.16.80.xxx Output: 1000 Mbit/s 0 errors, Input: 1000 Mbit/s 0 errors
area=20 CN2 172.17.80.xxx Output: 1000 Mbit/s 0 errors, Input: 1000 Mbit/s 0 errors
Checking network area 1 ...
Errors found in 172.16.4.111
ConfError: Suspected network loop, short interface block made on area=20 path=1
ConfError: Interface unblocked on area=20 path=1,
ConfError: Suspected network loop, short interface block made on area=20 path=1
ConfError: Suspected network loop, short interface block made on area=1 path=1
Errors found in 172.16.4.2
ConfError: Interface blocked aer detected network loop on area=20 path=0!!
ConfError: Interface unblocked on area=20 path=0,
Errors found in 172.16.4.181
ConfError: Interface blocked aer detected network loop on area=20 path=1!!
ConfError: Interface unblocked on area=20 path=1,
ConfError: Suspected network loop, short interface block made on area=1 path=1
ConfError: Interface blocked aer detected network loop on area=20 path=1!!
Hosts file update got reply from unknown node=1, area=201, Has address changed ?
Errors found in 172.16.4.183
ConfError: Suspected network loop, short interface block made on area=1 path=1
ConfError: Interface blocked aer detected network loop on area=20 path=1!!
ConfError: Interface unblocked on area=1 path=1,
ConfError: Interface unblocked on area=20 path=1,
Errors found in 172.16.4.220
ConfError: Suspected network loop, short interface block made on area=20 path=0
ConfError: Interface unblocked on area=20 path=0,
Errors found in 172.16.4.223
ConfError: Hosts file entry 172.16.4.222 corrected, wrong name for remote node
ConfError: Suspected network loop, short interface block made on area=1 path=1
ConfError: Suspected network loop, short interface block made on area=20 path=1
ConfError: Interface unblocked on area=1 path=1,
how to identify where is looped and how to solve it? need support
Voted best answer
Every node with RNRP periodically (once per second) send multicasted (to all) "hello" messages.
The hello message is interpreted by the RNRP service in all recipients and from that the nodes can deduct "who is on the network", etc. Other RNRP messages will tell how the network topology looks like, e.g. if there is a router node to a different area, etc.
The hello message contain a sequence counter which is the triggering factor behind the loop detection made by RNRP.
If too many (actually 13) hello messages with the *same* sequence counter is received within a too short time frame, a loop will be detected and countermeasures taken (blocking the Ethernet port). 7 seconds for first detection, 60 minutes for subsequent detection(s) if secondary network is available. If only one path is available, RNRP will continue with continuous 7 second blockages until no more loop is detected.
A loop can have many reasons; e.g. if you take an Ethernet cable and connect both ends to the same switch you have a loop.
Another, natural reason is if the network is configured for media redundancy:
- Spanning Tree (STP)
- Rapid Spanning Tree (RSTP)
- Hirschmann HIPER ring
- Westermo FRNT
- MOXA TurboRing
- MRP (https://en.wikipedia.org/wiki/Media_Redundancy_Protocol)
- Other vendors and additional media redundancy protocols exist
When a previously open ring (=flat network) is closed a ring will be the result and the redundancy protocol must now block one of the ring ports to avoid a loop.
This detection need to be ultra fast to prevent flooding the ring with packets (=storm).
A controller exposed to a network storm may become overloaded, drop connection with other nodes or in worse cases crash. Therefore, media redundancy protocols in the control network must be *superfine tuned* or else the storm may harm the PLC and cause problems or shutdowns. Some say rings add more problems than they solve. ABB recommend two separate networks to be used before rings.
STP and RSTP are by nature too slow. They can hardly work well in a control network given the time they take to stabilize the network.
Hirschmann's HIPER ring is said to detect in less than 100 millieseconds which is OK. So also the competitors MOXA, Westermo, etc.
But, the configuration of the ring protocol can be incorrect, or there can be firmware issues, etc. that allow a loop to exist too long time.
If RNRP perform a long block (1 hour) the loop has lasted at least 7 seconds which is way too long for a control network.
The messages above only list "Suspected" which is the short block (7 seconds) and could relate to a properly configured redundant network that sent out a few looped packets before it managed to figure out the new configuration and block one of the ring ports.
I suggest that you retrieve all AC 800M controller logs and also all C:\ProgramData\RnrpEvent.log files and examine them (they have timestamps) to see if any loop lasted longer than 7 seconds.
The example you inserted contain loop on both path0 and path1; the problem is likely spread over more than one physical network.
ABB recommend that path0 and path1 *never* share same physical hardware (e.g. same switch, same cable but using different VLAN, etc.).
Here is an example of a short block immediately followed by a long block:
29/5 *08:01:14.920 ConfError: Suspected network loop, short interface blockmade on area=1 path=0
29/5 *08:01:52.027 ConfError: Interface unblocked on area=1 path=0
29/5 *08:01:52.074 ConfError: Interface blocked after detected network loopon area=1 path=0!!
29/5 *09:01:46.165 ConfError: Interface unblocked on area=1 path=0
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