Vlag Capacities; Vlags Versus Port Trunks - Lenovo Flex System Fabric CN4093 Application Manual

VLAG Capacities

VLAGs versus Port Trunks

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CN4093 Application Guide for N/OS 8.2
Servers or switches that connect to the VLAG peers using a multi‐port VLAG are
considered VLAG clients. VLAG clients are not required to be VLAG‐capable. The
ports participating in the VLAG are configured as regular port trunks on the
VLAG client end.
On the VLAG peers, the VLAGs are configured similarly to regular port trunks,
using many of the same features and rules. See "Ports and Trunking" on page
for general information concerning all port trunks.
Each VLAG begins as a regular port trunk on each VLAG‐peer switch. The VLAG
may be either a static trunk group (portchannel) or dynamic LACP trunk group,
and consumes one slot from the overall port trunk capacity pool. The trunk type
must match that used on VLAG client devices. Additional configuration is then
required to implement the VLAG on both VLAG peer switches.
You may configure up to 64 trunk groups on the switch, with all types (regular or
VLAG, static or LACP) sharing the same pool.
The maximum number of configurable VLAG instances is as follows:
With STP off: Maximum of 31 VLAG instances

 With STP on:
PVRST/MSTP with one VLAG instance per VLAN/STG: Maximum of 31

VLAG instances
PVRST/MSTP with one VLAG instance belonging to multiple

VLANs/STGs: Maximum of 20 VLAG instances
Note: VLAG is not supported in RSTP mode.
Each trunk type can contain up to 16 member ports, depending on the port type
and availability.
Though similar to regular port trunks in many regards, VLAGs differ from regular
port trunks in a number of important ways:
A VLAG can consist of multiple ports on two VLAG peers, which are connected

to one logical client device such as a server, switch, or another VLAG device.
 The participating ports on the client device are configured as a regular port
trunk.
 The VLAG peers must be the same model, and run the same software version.
 VLAG peers require a dedicated inter‐switch link (ISL) for synchronization. The
ports used to create the ISL must have the following properties:
ISL ports must have VLAN tagging turned on.

ISL ports must be configured for all VLAG VLANs.

ISL ports must be placed into a regular port trunk group (dynamic or static).

A minimum of two ports on each switch are recommended for ISL use.

 Dynamic routing protocols, such as OSPF, cannot terminate on VLAGs.
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