Dynamic Learning Of Layer 3 Switching Rules; Layer 3 Switch Arp Table - Siemens RX1500 User Manual

Chapter 5
Setup and Configuration
NOTE
Only TCP and UDP traffic flows will be accelerated by the IP/Layer 3 switch fabric. Non-IP packet
types, such as ICMP and IGMP, will not be accelerated.
Section 5.31.1.3

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 SM, the maximum number of Layer 3 switching rules is 1000.
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
▪ Protocol
▪ Source TCP/UDP port
▪ Destination TCP/UDP port
This learning method is more granular and requires more ASIC resources, but it provides more flexibility in
firewall configuration as the rule takes the protocol and TCP/UDP port into consideration to make forwarding
decisions.
• Host-oriented learning is when the switch uses the following information to identify a traffic flow:
▪ Source IP address
▪ Destination IP address
This learning method provides less flexibility in firewall configuration, as the user can allow or disallow traffic
between two hosts.
For unicast traffic, each flow constitutes one rule. For multicast routing, one multicast route may constitute several
rules.
The Layer 3 switch continuously monitors activity (this is, the presence of traffic) for dynamically learned rules.
Because of this, dynamically learned rules may be removed after a configurable time due to inactivity.
Section 5.31.1.4

Layer 3 Switch ARP Table

A router needs to know the destination host or next-hop gateway MAC address for it to forward a packet on the
other subnet. Therefore, software maintains an Address Resolution Protocol (ARP) table that maps IP addresses
670 Dynamic Learning of Layer 3 Switching Rules
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