3Com S7906E - Switch, Руководство по настройке

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3-2
z
exp-dp : EXP-to-drop priority mapping table.
The default priority mapping tables (as shown in Appendix B Default Priority Mapping Tables ) are
available for priority mapping. Generally, they are sufficient for priority mapping. If a default priority
mapping table cannot meet your requirements, you can modify the priority mapping table as required.
Priority Trust Mode on a Port
The priority trust mode on a port decides which priority is used for priority mapping table lookup. There
are two priority trust modes on the S7900E series switches:
z
dot1p : Uses the 802.1p priority carried in packets for priority mapping.
z
dscp : Uses the DSCP carried in packets for priority mapping.
In addition, port priority was introduced for 802.1q untagged packets. Thus, when a port configured with
the 802.1p trust mode receives an 802.1q untagged packet, the priority of the port is used as the 802.1p
priority of the packet for priority mapping table lookup.
The priority mapping procedure varies with the priority modes, as described in the next section Priority
Mapping Procedure .
Priority Mapping Procedure
Figure 3-1 presents how the S7900E performs priority mapping for an Ethernet packet. The procedure
differs depending on whether the packet is 802.1q tagged or not.
Figure 3-1 Priority mapping procedure for an Ethernet packet
Which priority is
trusted on the
port?
Receive a
packet on a port
Use the port
priority as the
802.1p priority of
the packet
Look up the
dot1p-dp and
dot1p-lp tables
Mark the packet
with local
precedence and
drop precedence
Is the packet
802.1q tagged?
DSCP in packets
Look up the
dscp-dp, dscp-
dot1p, and dscp-
dscp tables
802.1p in
packets
Mark the packet
with 802.1p
priority, drop
precedence, and
new DSCP
precedence
Look up the
dot1p-lp table
Mark the packet
with local
precedence
Look up the
dot1p-dp and
dot1p-lp tables
Mark the packet
with local
precedence and
drop precedence
Schedule the packet
according to its local
precedence and drop
precedence
Y
N