Users Guide

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VLAN Scaling
When VLANs are created, traffic class is specified for each VLAN that maps the VLAN traffic to a specific queue on the egress
port. Class-maps are created for each VLAN matching and the action is specified in the policymap that maps it to a specific
traffic class. Using traffic class-to-queue mapping, the traffic gets mapped to the corresponding queue.
Since ACL rules are created on a per VLAN basis, the scale of VLANs is dependent on the number of ACL rules available. The
ACL space is also shared by other applications such as FCoE. When more VLANs are created, the L2 QoS ACL space for the
VLAN ACLs get exhausted. If the VLAN ACL creation fails, it results in VLAN creation failure. As a result, there cannot be more
than 256 VLANs in Fabric mode.
When a VLAN is created with the uplink ports, a traffic class such as gold, silver, or platinum is assigned to the traffic on the
VLAN. On receiving the configuration from GUI through DNV, the Fabric agent creates a classmap of type qos with the name
CM<vlanid> which matches the same <vlanid>. For example when vlanid 100 with a traffic class of type 4 the classmap created
will be:
classmap type qos CM100
match vlan 100
A single policymap is created to hold all the VLAN classmaps and its applied at the system qos level which gets applied to all the
interfaces.
policymap type qos PM_VLAN
class CM100
set qos-group 4
Any addition, deletion, or modification to the VLAN or the traffic class happens within the same policymap.
In the NPU, each classmap maps to an ACL entry in the L2QOS region matching the vlanid in the classmap.
Constraints
VLAN scaling is limited to the Fabric mode.
Currently Dynamic ARP Inspection (DAI) uses the vlan-group id. NAS implicitly programs the VLAN-group id in the Vlan table.
But DAI feature is not enabled in Fabric mode.
Use of vlan-group id is limited only to applications which require grouping for the purpose of using ACLs.
Anycast IP Gateway for VLANs
Anycast IP is a network addressing and routing method that allows for multiple devices to share the same IP address in a
network.
Starting with Release 10.5.2.0, you can configure anycast IP functionality for VLAN interfaces in a VLT domain. In earlier
releases, this feature was applicable only for the virtual-network interfaces. For more information, see Enable overlay routing
between virtual networks.
Anycast IP is a lightweight gateway router redundancy protocol that allows the hosts to use a virtual IP and a virtual MAC
address to forward traffic out of a VLT domain. You can configure virtual IP addresses on VLAN interfaces in addition to a
primary address, and the anycast gateway MAC address is configured to be the same on all the VLT switches. This configuration
allows devices to use a common IP address as their network gateway. The VLT domain-specific information is used to determine
the primary node, which responds to ARP requests for anycast IP. If the primary VLT node goes down, the secondary VLT node
owns the gateway IP addresses and starts responding to ARP requests.
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