Deployment Guide

L2 (MAC) and TCAM (ACL)Table

The NEC PFC controller can only install flows in the TCAM (ACL) table. This limits the maximum flows that can be installed on the switch

to the limited size of the TCAM. The OpenFlow Ethernet Fabric (OEF) architecture is implemented by NEC PFC to expand the OF flow

table’s on a switch to include two tables – L2 (MAC) table and TCAM (ACL) table. The L2 table allows L2 forwarding based on VLAN +

DMAC. It does away with the requirement of using the much smaller ACL table for L2 forwarding. This allows scaling up the number of

flows handled by the switch without being limited by the ACL table. The ACL table can then be used for more ACL rules or entries to over-

ride L2 table based forwarding cases. The OEF model thus allows the controller to scale the ACL flows configurable and the OF switch to

scale the L2 (MAC) flows to the maximum size of the MAC table. Another advantage is that the number of packet-ins sent to the

controller are reduced, as the switch installs the learnt MAC flows.

This model needs configuration on the OF switch. CLI commands are available to configure the OF instance — “vlan learn”, for enabling

learning on all vlans and “L2 MacLearn Mode” for installing the learnt MAC flows on the switch. The switch will automatically populate the

L2 (MAC) table.

The image below shows the two tables — L2 and TCAM table on the switch. The external table id’s are “20” for L2 table and “40” for

TCAM table.

NEC Controller

Switch Hardware

OF messages

Flow: Add, Mod, Delete

Flow get: Multi-part

External table 20

L2 Table

External table 40

TCAM Table

Switch Software

OF messages

Flow: Mod, Delete

Flow get: Multi-part

For a switch to operate in the above mode, the user needs to configure “l2–maclearn-mode enable” on an OF instance. Under this mode

“MAC learning” will be enabled on all OF ports against that OF-instance. Entries in the L2 table will be internally added by switch software

on learning a new MAC address. L2 table information can be retrieved by the controller using Multi-part request. The controller can delete

an L2 table entry using flow delete message.

MAC Aging

The hardware informs the software of the aged MAC address. Switch software will find the corresponding flow entry and remove the

MAC from the flow table. The MAC address is then flushed from the hardware.

Introduction