Subnet-Based Vlan Guidelines - Avaya 8800 Planning And Engineering, Network Design

Layer 3 network design
RSMLT L2 Edge provides:
• Greater scalability—VRRP scales to 255 instances, while RSMLT scales to the maximum
number of VLANs.
• Simpler configuration—Simply enable RSMLT on a VLAN; VRRP requires virtual IP
configuration, along with other parameters.
For connections in pure Layer 3 configurations (using a static or dynamic routing protocol), a Layer
3 RSMLT configuration is recommended over VRRP. In these instances, an RSMLT configuration
provides faster failover than one with VRRP because the connection is a Layer 3 connection, not
just a Layer 2 connection for default gateway redundancy.
Both VRRP and RSMLT can provide default gateway resiliency for end stations. The configurations
of these features are different, but both provide the same end result and are transparent to the end
station.
For more information about RSMLT, see

Subnet-based VLAN guidelines

You can use subnet-based VLANs to classify end-users in a VLAN based on the end-user source IP
addresses. For each packet, the switch performs a lookup, and, based on the source IP address
and mask, determines to which VLAN the traffic belongs. To provide security, subnet-based VLANs
can be used to allow only users on the appropriate IP subnet to access to the network.
You cannot classify non-IP traffic using a subnet-based VLAN.
You can enable routing in each subnet-based VLAN by assigning an IP address to the subnet-
based VLAN. If no IP address is configured, the subnet-based VLAN is in Layer 2 switch mode only.
You can enable VRRP for subnet-based VLANs. The traffic routed by the VRRP Master interface is
forwarded by hardware. Therefore, no throughput impact is expected when you use VRRP on
subnet-based VLANs.
You can use subnet-based VLANs to achieve multinetting functionality; however, multiple subnet-
based VLANs on a port can only classify traffic based on the sender IP source address. Thus, you
cannot multinet by using multiple subnet-based VLANs between routers (Layer 3 devices).
Multinetting is supported, however, on all end-user-facing ports.
You cannot classify Dynamic Host Configuration Protocol (DHCP) traffic into subnet-based VLANs
because DHCP requests do not carry a specific source IP address; instead, they use an an all
broadcast address. To support DHCP to classify subnet-based VLAN members, create an overlay
port-based VLAN to collect the bootp/DHCP traffic and forward it to the appropriate DHCP server.
After the DHCP response is forwarded to the DHCP client and it learns its source IP address, the
end-user traffic is appropriately classified into the subnet-based VLAN.
The switch supports a maximum number of 200 subnet-based VLANs.
June 2016
Routed SMLT on page 86.
Planning and Engineering — Network Design
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