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What are the networking layer 2 reachability requirements in ONTAP 9?

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Applies to

ONTAP 9

Answer

  • In order to identify OSI layer 2 reachability issues, an L2 algorithm is used to ping the MAC addresses of the other ports in the cluster that belong to the same broadcast domain.
  • The L2 ping is performed by sending Connectivity Fault Management (CFM) frames 
  • A port considers itself 'healthy' if it receives a CFM frame from any other port in its configured broadcast domain
  • A port considers itself 'degraded' if it is receives no CFM frames from its configured broadcast domain

Example:

  1. Four ports across two nodes are configured to belong to the storage-side broadcast domain TEST 
    • node1:e0a
    • node1:e0b
    • node2:e0a 
    • node2:e0b
  2. On the switch side, all 4 ports are expected to be configured on switch-side VLAN 10
    • Accidentally, one port node2:e0b is configured on switch-side VLAN 20
  3. The 3 ports on VLAN 10 can L2 ping each other and will be marked as healthy.
    • node1:e0a on VLAN10 sends CFM frames towards the other ports that belong to storage-side broadcast domain TEST ​​​​
    • The switch successfully forwards the CFM frames to the ports on VLAN 10
    • node1:e0a is marked as healthy
    • The process is repeated for ports node1:e0b and node2:e0a 
  4. Since it is in VLAN 20, port node2:e0b on VLAN 20 will be unable to L2 ping the other 3 ports , so will be marked degraded.
    • node2:e0b on VLAN20 sends CFM frames towards the other ports that belong to storage-side broadcast domain TEST ​​​​
    • The switch is not configured to forward traffic from VLAN 20 to VLAN 10, so the CFM frames do not read the ports on VLAN 10
    • node2:e0b is marked as degraded
  5. In this example, the storage-side configured broadcast domain does not match the switch-side configured broadcast domains
    • According to the storage-side configuration, the ports are all in a single broadcast domain TEST, and therefore are expected have L2 reachability
    • According to the switch-side configruation, the ports are spread across two separate broadcast domains VLAN 10 and VLAN 20, and therefore lack L2 connectivity
    • Port(s) was marked degraded when ONTAP detected that the storage-side and switch-side broadcast domain configurations do not match


::*> broadcast-domain show -broadcast-domain TEST
  (network port broadcast-domain show)
IPspace Broadcast                                         Update
Name    Domain Name    MTU  Port List                     Status Details
------- ----------- ------  ----------------------------- --------------
Default TEST       1500
                            node1:e0a               complete
                            node1:e0b               complete
                            node2:e0a               complete
                            node2:e0b               complete


::> net port show -health
  (network port show)
                          Health
Node       Port      Link Status   Degraded Reasons
--------   --------- ---- -------- -----------------------
node1
           e0a       up   healthy  -
           e0b       up   healthy  -

node2
           e0a       up   healthy  -
           e0b       up   degraded l2_reachability 

Note: node2:e0b is the switch-side VLAN 20 port.

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