D-Link DES 6000 Product Manual - Page 27

Packet Forwarding, Spanning Tree Algorithm, Aging Time, Filtering Database - manual

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Modular Ethernet Switch User's Guide Packet Forwarding The Switch learns the network configuration and uses this information to forward packets. This reduces the traffic congestion on the network, because packets, instead of being transmitted to all segments, are transmitted to the destination only. Example: if Port 1 receives a packet destined for a station on Port 2, the Switch transmits that packet through Port 2 only, and transmits nothing through the other ports. Aging Time The Aging Time is a parameter that affects the auto-learn process of the Switch in terms of the network configuration. Dynamic Entries, which make up the auto-learned-node address, are aged out of the address table according to the Aging Time that you set. The Aging Time can be from 10 seconds to 9999 seconds. A very long Aging Time can result with the out-ofdate Dynamic Entries that may cause incorrect packet filtering/forwarding decisions. On the other hand, if the Aging Time is too short, many entries may be aged out soon, resulting in a high percentage of received packets whose source addresses cannot be found in the address table, in which case the Switch will broadcast the packet to all ports, negating many of the benefits of having a switch. Filtering Database A switch uses a filtering database to segment the network and control communications between segments. It also filters packets off the network for intrusion control (MAC Address filtering). For port filtering, each port on the switch is a unique collision domain and the switch filters (discards) packets whose destination lies on the same port as where it originated. This keeps local packets from disrupting communications on other parts of the network. For intrusion control, whenever a switch encounters a packet originating from or destined to a MAC address defined by the user, the switch will discard the packet. Filtering includes: 1. Dynamic filtering Automatic learning and aging of MAC addresses and their location on the network. Filtering occurs to keep local traffic confined to its segment. 2. MAC address filtering The manual entry of specific MAC addresses to be filtered from the network. 3. Filtering done by the Spanning Tree Protocol Can filter packets based on topology, making sure that signal loops don't occur. 4. Filtering done for VLAN integrity Packets from a member of a VLAN (VLAN 2, for example) destined for a device on another VLAN (VLAN 3) will be filtered. Spanning Tree Algorithm The Spanning Tree Algorithm (STA) in the Switch allows you to create alternative paths (with multiple switches or other types of bridges) in your network. These backup paths are idle until the Switch determines that a problem has developed in the primary paths. When a primary path is lost, the switch providing the alternative path will automatically go into service with no operator intervention. This automatic network reconfiguration provides maximum uptime to network users. The concept of the Spanning Tree Algorithm is a 22 Switch Management Concepts

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Modular Ethernet Switch User’s Guide
22
Switch Management Concepts
Packet Forwarding
The Switch learns the network configuration and uses this information to forward packets. This reduces the
traffic congestion on the network, because packets, instead of being transmitted to all segments, are
transmitted to the destination only.
Example:
if Port 1 receives a packet destined for a station on Port 2, the
Switch transmits that packet through Port 2 only, and transmits nothing through the other ports.
Aging Time
The Aging Time is a parameter that affects the auto-learn process of the Switch in terms of the network
configuration. Dynamic Entries, which make up the auto-learned-node address, are aged out of the address
table according to the Aging Time that you set.
The Aging Time can be from 10 seconds to 9999 seconds. A very long Aging Time can result with the out-of-
date Dynamic Entries that may cause incorrect packet filtering/forwarding decisions.
On the other hand, if the Aging Time is too short, many entries may be aged out soon, resulting in a high
percentage of received packets whose source addresses cannot be found in the address table, in which case the
Switch will broadcast the packet to all ports, negating many of the benefits of having a switch.
Filtering Database
A switch uses a filtering database to segment the network and control communications between segments.
It also filters packets off the network for intrusion control (MAC Address filtering).
For port filtering, each port on the switch is a unique collision domain and the switch filters (discards)
packets whose destination lies on the same port as where it originated. This keeps local packets from
disrupting communications on other parts of the network.
For intrusion control, whenever a switch encounters a packet originating from or destined to a MAC
address defined by the user, the switch will discard the packet.
Filtering includes:
1. Dynamic filtering
Automatic learning and aging of MAC addresses and their location on the
network. Filtering occurs to keep local traffic confined to its segment.
2. MAC address filtering
The manual entry of specific MAC addresses to be filtered from the network.
3. Filtering done by the Spanning Tree Protocol
Can filter packets based on topology, making sure
that signal loops don’t occur.
4. Filtering done for VLAN integrity
Packets from a member of a VLAN (VLAN 2, for example)
destined for a device on another VLAN (VLAN 3) will be filtered.
Spanning Tree Algorithm
The Spanning Tree Algorithm (STA) in the Switch allows you to create alternative paths (with multiple
switches or other types of bridges) in your network. These backup paths are idle until the Switch determines
that a problem has developed in the primary paths. When a primary path is lost, the switch providing the
alternative path will automatically go into service with no operator intervention. This automatic network
reconfiguration provides maximum uptime to network users. The concept of the Spanning Tree Algorithm is a