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Chapter 9

Layer 3

RUGGEDCOM ROX II

CLI User Guide

316 Static Layer 3 Switching Rules

NOTE

In a Layer 2 switched network segment, a VLAN constitutes an IP subnet.

• Next-hop gateway Media Access Control (MAC) address: this information is stored in the router's ARP Table.

NOTE

If the next hop is the destination subnet itself, then the destination host MAC address is required.

A Layer 3 Switch uses the routing information listed above and translates it into Layer 3 switching rules. These

rules are known as the Layer 3 Switch Forwarding Information Base (FIB) or the Layer 3 Switch Forwarding Table.

A Layer 3 switching rule is actually a set of parameters identifying a traffic flow to be switched and determining

how to perform the switching.

Layer 3 switching Application-Specific Integrated Circuits (ASICs) store Layer 3 switching rules in a Ternary Content

Addressable Memory (TCAM) table. Layer 3 switching rules can be statically configured or dynamically learned

(also known as auto-learned).

Section9.1.2

Static Layer 3 Switching Rules

When creating a static route through switch management, hardware acceleration can be explicitly configured. If

hardware acceleration is selected, an appropriate Layer 3 switching rule is installed in the ASIC's TCAM and never

ages out.

NOTE

Only TCP and UDP traffic flows will be accelerated by the IP/Layer 3 switch fabric.

Section9.1.3

Dynamic Learning of Layer 3 Switching Rules

For static routes without hardware acceleration or for dynamic routes, Layer 3 switching rules can be dynamically

learned based on software-based router and firewall decisions. For example, the Layer 3 switch can automatically

decide to offload some flows from the router into the Layer 3 Forwarding Table.

After a certain amount of traffic for the same flow is successfully routed, the Layer 3 switching ASIC begins

switching the rest of the packets belonging to the same flow. A flow is unidirectional traffic between two hosts.

For example, traffic flowing between ports from one host to another is considered a flow. Traffic flowing in the

opposite direction between the same ports is considered a different flow.

NOTE

For 8G or 88G SM, the maximum number of Layer 3 switching rules is 1000 or 3000 respectively.

Different auto-learning methods may be used:

• Flow-oriented learning is when the switch uses the following information to identify a traffic flow:

▫ Source IP address

▫ Destination IP address

Siemens RUGGEDCOM ROX II User Manual

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