Vlans And Routing; Virtual Routing Between Vlans - Avaya 8800 Configuration Manual

Routing fundamentals

VLANs and routing

When traffic is routed on a virtual local area network (VLAN), an IP address is assigned to the
VLAN and is not associated with any particular physical port. Brouter ports use single-port
VLANs to route IP packets and bridge nonroutable traffic in specifically assigned VLANs.

Virtual routing between VLANs

The Avaya Ethernet Routing Switch 8800/8600 supports wire-speed IP routing between
VLANs. As shown in the following figure, although VLAN 1 and VLAN 2 are on the same switch,
for traffic to flow from VLAN 1 to VLAN 2, the traffic must be routed.
Figure 3: IP routing between VLANs
When you configure routing on a VLAN, you assign an IP address to the VLAN, which acts as
a virtual router interface address for the VLAN (a virtual router interface is so named because
it is associated with no particular port). Through any VLAN port, you can reach the VLAN IP
address, and frames are routed from the VLAN through the gateway IP address. Routed traffic
is forwarded to another VLAN within the switch.
When Spanning Tree Protocol is enabled on a VLAN, spanning tree convergence must be
stable before the routing protocol begins. This requirement can lead to an additional delay in
forwarding IP traffic.
Because a port can belong to multiple VLANs (some of which are configured for routing on the
switch and some of which are not), a one-to-one correspondence no longer exists between
the physical port and the router interface.
As with any IP address, virtual router interface addresses are also used for device
management. For Simple Network Management Protocol (SNMP) or Telnet management, you
16 Configuration — OSPF and RIP June 2011