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Cisco Bug: CSCun20338 - Active ERSPAN session(s), may impact PTP synchronisation

Last Modified

Feb 14, 2018

Products (2)

  • Cisco Nexus 3000 Series Switches
  • Cisco Nexus 3548 Switch

Known Affected Releases

6.0(2)A1(1a)

Description (partial)

Symptom:
PTP slave/client chassis, connected to Nexus 3548 master, may unexpectedly report high offset. 
If two Nexus 3548 paired, under same conditions, device(s) which play(s) role of PTP Slave, may be reporting bad-correction. 

Please see 'conditions' section for more information.

Conditions:
Issue observed under two next conditions (both should be met): 
*** PTP master interface(s) configured with non default synchronisation interval; 
*** active ERSPAN session (which is sourced on PTP master N3548 switch) egresses PTP master interface, configured with non default synchronisation interval.

Thus, when two Nexus 3548 interconnected and above conditions were met, PTP Client switch may be reporting issue. For example, A_SW is PTP master, connected to B_SW over interface Eth1/47, then:

A_SW # show running-config ptp 
/*snip*/
interface Ethernet1/47
  ptp
  ptp vlan ABCD
  ptp sync interval -2
  ptp delay-request minimum interval 0
/*snip*/

A_SW# LYA# show monitor session all 
   session 1
---------------
type              : erspan-source
state             : up
granularity       : 100 nanoseconds
erspan-id         : 1
vrf-name          : default
destination-ip    : a.b.x.y  <<< IP address reachable over local Eth1/47
ip-ttl            : 1
ip-dscp           : 0
header-type       : 2
origin-ip         : a.b.c.d (global)
source intf       : 
    rx            : Eth1/1        
    tx            : Eth1/1        
    both          : Eth1/1        
source VLANs      : 
    rx            : 


B_SW# show system internal ptp bad-corrections 
PTP past corrections
-----------------------------------------------------------------------------------------------------------------------------------------------------------
Slave Port              SUP Time               Correction(ns)    MeanPath Delay(ns)   MasterTimestamp (sec, nsec)    Slave Timestamp (sec, nsec) Sync-SeqID
----------  -------------------------------  ------------------  ------------------  ------------------  ---------  ------------------  ---------  --------
Eth1/47     Sun Feb 16 12:59:06 2014 176750  904456148           97                  1392555546          176070225  1392555545          271614174  41740  
Eth1/47     Sun Feb 16 19:38:49 2014 245850  742818154           96                  1392579529          141778735  1392579528          398960677  17514  
Eth1/47     Sun Feb 16 19:38:49 2014 292773  -742818145          96                  1392579529          398966465  1392579530          141784706  17770  
Eth1/47     Mon Feb 17 02:50:00 2014 792762  864389960           94                  1392605400          794363408  1392605399          929973542  17871  
Eth1/47     Mon Feb 17 08:16:37 2014 751786  872444645           97                  1392624997          751602344  1392624996          879157796  50715  
Eth1/47     Mon Feb 17 08:16:37 2014 875595  -872444646          97                  1392624997          879023277  1392624998          751468020  50971
/*snip*/

In case if PTP capable server connected to Nexus 3548 in same way, detecting of actual offset drift will depend on implementation. Please refer to proper documentation for more information.
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