3Com 3C17705, User Manual

Page: 82 / 184

82 C
HAPTER
5: F
ORWARDING
D
ATABASE
(FDB)
way of the command-line interface are stored as permanent. The
switch can support a maximum of 64 permanent entries.
Once created, permanent entries stay the same as when they were
created. For example. the permanent entry store is not updated when
any of the following take place:
■
A VLAN is deleted.
■
A VLANid is changed.
■
A port mode is changed (tagged/untagged).
■
A port is deleted from a VLAN.
■
A port is disabled.
■
A port enters blocking state.
■
A port QoS setting is changed.
■
A port goes down (link down).
■
Blackhole entries — A blackhole entry configures packets with a
specified MAC destination address to be discarded. Blackhole entries
are useful as a security measure or in special circumstances where a
specific destination address must be discarded. Blackhole entries are
treated like permanent entries in the event of a switch reset or power
off/on cycle. Blackhole entries are never aged out of the database.
How FDB Entries Get
Added
Entries are added into the FDB in the following two ways:
■
The switch can learn entries. The system updates its FDB with the
source MAC address from a packet, the VLAN, and the port identifier
on which the source packet is received.
■
You can enter and update entries using a MIB browser, an SNMP
Network Manager, or the command-line interface (CLI).
Associating a QoS
Profile with an FDB
Entry
You can associate a QoS profile with a MAC address (and VLAN) of a
device that will be dynamically learned. The FDB treats the entry like a
dynamic entry (it is learned, it can be aged out of the database, and so
on). The switch applies the QoS profile as soon as the FDB entry is
learned.
For more information on QoS, refer to Chapter 7 .