Concept Guide

VLT Dual Homing scenarios
In a VLT dual homing setup, if the same PE units (maximum of 80 PE units) are congured in both the VLT CB nodes before the VLT pairing
is up, the PEX port counts on both the modes is the same after the VLT pairing is up.
However, if separate PE units (maximum of 80 PE units) are congured in each VLT CB node before the VLT pairing is up, the PEs may not
get synchronized properly after the VLT pairs come up. This is an erroneous conguration that may cause the system to become unstable.
To indicate this error state, a port validation error (PVE) is included in the show pe command output.
If the remote PE sync from the primary VLT CB node results in the PEX port count to exceed the prescribed hard-limit (4000), all the PEs
in the secondary VLT CB node are shown to be in PVE state.
Also, the system logs the following syslog message:
Secondary unit is in error state as the maximum number of PE ports limit reached!. Correct the
configuration and re-establish VLT to recover the system!.
To recover the secondary VLT CB node, you must congure the same PE units (maximum of 80 PE units) in both the VLT CB nodes and
re-establish the VLT connection.
For more information on dual homing, see Dual Homing.
PE Selection Logic
After you provision port extenders and power them on, the PEs come online according to the selection logic in the scenarios described in
this section.
• You may provision cascade ports for dierent PEs but connect the cascade ports to the same PE. In this case, only the PE with lowest
PE ID comes online. In the following example, both cascade ports 1/0 and 1/12 are cabled to the same PE. However, port 1/0 is
provisioned for PE 10; port 1/12 is provisioned for PE 20. As a result, only PE 10 comes online. PE 20 remains oine and its congured
cascade port is placed in an error state.
Dell# show running-config pe
!
feature extended-bridge
!
pe provision 10
cascade interface TenGigabitEthernet 1/0
stack-unit 0 type C1048P
stack-unit 0 priority 1
!
pe provision 20
cascade interface TenGigabitEthernet 1/12
Dell# show pe brief
- Port Extenders Information --
----------------------------------------------------------
PE-id Status Stack-size Type System-MAC
----------------------------------------------------------
10 online 1 C1048P a0:68:00:3f:92:bc
20 offline 1 C1048P 00:00:00:00:00:00
Dell#show pe errors
PE-id: 10
PE MAC: a0:68:00:3f:92:bc
Interface Errors:
TenGigabitEthernet 1/12 - Error State
• You may connect two PEs to a parent C9010 but only provision one PE with cascade ports. In this case, only the PE connected to the
lowest numbered cascade port comes online. In the following example, PE 10 is provisioned with cascade ports 1/0, 8, and 12. However,
Port Extenders (PEs)
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