IBM 8275-416, User Manual

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Once Self Learning IP is enabled, the following information is available:
v
Self Learning IP statistics for the switch (see Switch Detailed Statistics Menu in
Chapter 4).
v
IP and MAC addresses of routers learned (see Self Learning IP Router Table
Menu in Chapter 4).
v
Host IP statistics (see Self Learning IP Host Address Menu in Chapter 4).
Note that the Packets Switched count included in the Switch Detailed Statistics
Menu may not reflect the absolute latest value. The information used for updating
this count is obtained as individual Host Table entries are refreshed, so while this
value can change over time, it does not necessarily update at the same frequency
as other statistics on the menu.
While intended as an autonomous feature, Self Learning IP is affected by certain
changes in switch configuration. If Self Learning IP is enabled and the switch IP
address is reset, the Self Learning IP function is automatically disabled. The Self
Learning IP Router and Host Tables are cleared whenever there is a link
aggregation configuration change (see Link aggregation (trunking) in this chapter),
forcing router and host devices to be relearned.
Link aggregation (trunking)
Link aggregation, also called trunking allows 802.3 MAC interfaces to be grouped
together logically to appear as one super-link. The super-link or Link Aggregation
Group (LAG) has access to the combined bandwidth of all links.
The Sun Trunking
™
1.0 specification is supported for the 10/100BASE-TX and
100BASE-FX ports. All members of the trunk must support Sun Trunking
™
1.0. For
information about configuring trunks, see “Trunk management menu” on page 58.
Up to 8 trunks can be configured.
Advantages of trunking are:
v
Fault tolerance: Failure of one or more of the links in the LAG are handled
gracefully. If a link of the LAG fails, the flows mapped to that link are dynamically
reassigned to the remaining links of the LAG.
v
Redundancy: Link aggregation also provides automatic, point-to-point redundancy
between two devices (switch-to-switch).
Fast spanning tree mode
The IEEE 802.1D spanning tree protocol (STP) is designed to prevent loops in
Ethernet networks. To achieve this objective the STP does not allow switches to
forward data frames on a link immediately after the link is activated. The STP first
listens for spanning tree BPDUs from other switches, then determines whether to
put the link into forwarding state. When a default IEEE spanning tree timer value of
15 seconds is used for the forward delay timer, a link can start forwarding traffic 30
seconds after it becomes active on the network.
In networks with shared media hubs, there is a trend to attach network stations (or
hosts) directly to multi-port bridges (otherwise known as switches). Unfortunately,
the 802.1D spanning tree protocol has not been changed to accommodate this
trend. So, when a network station is ready to send data, the switch does not allow
the network station to communicate on the network until STP puts the port in
forwarding state. The 30 second delay forces the network station users to wait
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8275-416 User’s Guide