Ethernet ports can record and recognize various medium statistics and errors. There are two main types of errors:
Frame Based — Frame based errors are counted when the arriving frame has an error that means the frame is invalid. These types of errors are only detectable when frames are presents on the wire.
Symbol Based — Symbol errors are invalidly encoded symbols on the physical medium. Symbols are always present on an active Ethernet port regardless of the presence of frames.
CRC-Monitor and Symbol-Monitor allows the operator to monitor ingress error conditions on the Ethernet medium and compare these error counts to the thresholds. CRC-Monitor monitors CRC errors. Symbol-Monitor monitors symbol errors. Symbol Error is not supported on all Ethernet ports. Crossing a signal degrade (SD) threshold causes a log event to be raised. Crossing the configured signal failure (SF) threshold causes the port to enter an operation state of down. The operator may consider the configuration of other protocols to convey the failure, through timeout conditions.
The error rates are in the form of M*10E-N. The operator has the ability to configure both the threshold (N) and a multiplier (M). By default if the multiplier is not configured the multiplier is 1. As an example, sd-threshold 3 would result in a signal degrade error rate of 1*10E-3 (one error per 1000). Changing the configuration to would sd-threshold 3 multiplier 5 result in a signal degrade rate of 5*10E-3 (5 errors per 1000). The signal degrade value must be a lower error rate than the signal failure threshold. This threshold can be used to provide notification that the port is operating in a degraded but not failed condition. These do not equate to a bit error rate (BER). CRC-Monitor provides a CRC error rate. Symbol-Monitor provides a symbol error rate.
The configured error thresholds are compared to the operator specified sliding window to determine if one or both of the thresholds have been crossed. Statistics are gathered every second. This means that every second the oldest statistics are dropped from the calculation. The default 10 second sliding window means that at the 11th second, the oldest 1-second statistical data is dropped and the 11th second is included.
Symbol error crossing differs slightly from CRC-based error crossing. The error threshold crossing is calculated based on the window size and the fixed number of symbols that arrive (ingress) on that port during that window. The following configuration demonstrates this concept.
config>port>ethernet# info detail
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symbol-monitor
sd-threshold 5 multiplier 5
sf-threshold 3 multiplier 5
no shutdown
exit
show port 2/1/2 ethernet
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Ethernet Interface
===============================================================================
Description : 2/1/2
Interface : 2/1/2 Oper Speed : N/A
Link-level : Ethernet Config Speed : 1 Gbps
Admin State : down Oper Duplex : N/A
Oper State : down Config Duplex : full
Physical Link : No MTU : 9212
Single Fiber Mode : No Min Frame Length : 64 Bytes
IfIndex : 69271552 Hold time up : 0 seconds
Last State Change : 06/29/2014 05:04:12 Hold time down : 0 seconds
Last Cleared Time : N/A DDM Events : Enabled
Phys State Chng Cnt: 0
Configured Mode : network Encap Type : null
Dot1Q Ethertype : 0x8100 QinQ Ethertype : 0x8100
PBB Ethertype : 0x88e7
Ing. Pool % Rate : 100 Egr. Pool % Rate : 100
Ing. Pool Policy : n/a
Egr. Pool Policy : n/a
Net. Egr. Queue Pol: default
Egr. Sched. Pol : n/a
Auto-negotiate : true MDI/MDX : unknown
Oper Phy-tx-clock : not-applicable
Accounting Policy : None Collect-stats : Disabled
Acct Plcy Eth Phys : None Collect Eth Phys : Disabled
Egress Rate : Default Ingress Rate : Default
Load-balance-algo : Default LACP Tunnel : Disabled
Down-when-looped : Disabled Keep-alive : 10
Loop Detected : False Retry : 120
Use Broadcast Addr : False
Sync. Status Msg. : Disabled Rx Quality Level : N/A
Tx DUS/DNU : Disabled Tx Quality Level : N/A
SSM Code Type : sdh
Down On Int. Error : Disabled
CRC Mon SD Thresh : Disabled CRC Mon Window : 10 seconds
CRC Mon SF Thresh : Disabled
Sym Mon SD Thresh : 5*10E-5 Sym Mon Window : 10 seconds
Sym Mon SF Thresh : 5*10E-3 Tot Sym Mon Errs : 0
EFM OAM : Disabled EFM OAM Link Mon : Disabled
Configured Address : 8c:90:d3:a0:c7:42
Hardware Address : 8c:90:d3:a0:c7:42
Transceiver Data
Transceiver Status : not-equipped
===============================================================================
Traffic Statistics
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Input Output
-------------------------------------------------------------------------------
Octets 0 0
Packets 0 0
Errors 0 0
Utilization (300 seconds) 0.00% 0.00%
===============================================================================
===============================================================================
Port Statistics
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Input Output
-------------------------------------------------------------------------------
Unicast Packets 0 0
Multicast Packets 0 0
Broadcast Packets 0 0
Discards 0 0
Unknown Proto Discards 0
===============================================================================
===============================================================================
Ethernet-like Medium Statistics
===============================================================================
Alignment Errors : 0 Sngl Collisions : 0
FCS Errors : 0 Mult Collisions : 0
SQE Test Errors : 0 Late Collisions : 0
CSE : 0 Excess Collisns : 0
Too long Frames : 0 Int MAC Tx Errs : 0
Symbol Errors : 0 Int MAC Rx Errs : 0
In Pause Frames : 0 Out Pause Frames : 0
===============================================================================
The above configuration results in an SD threshold of 5*10E-5 (0.00005) and an SF threshold of 5*10E-3 (0.005) over the default 10-second window. If this port is a 1GbE port supporting symbol monitoring then the error rate is compared against 1,250,000,000 symbols (10 seconds worth of symbols on a 1GbE port 125,000,000). If the error count in the current 10 second sliding window is less than 62,500 then the error rate is below the signal degrade threshold and no action is taken. If the error count is between 62,501 and 6,250,000 then the error rate is above signal degrade but has not breached the signal failure signal threshold and a log event is raised. If the error count is above 6,250,000 the signal failure threshold is crossed and the port enters an operation state of down. Consider that this is a very simple example meant to demonstrate the function and not meant to be used as a guide for configuring the various thresholds and window times.
A port is not returned to service automatically when a port enters the failed condition as a result of crossing a signal failure threshold for both CRC-Monitor and Symbol-Monitor. Because the port is operationally down without a physical link error monitoring stops. The operator may enable the port using the shutdown and no shutdown port commands. Other port transition functions like clearing the MDA or slot, removing the cable, and other physical link transition functions.