Extreme Networks BlackDiamond 6800 MPLS, Инструкция по установке и эксплуатации, Страница: 51 / 176

MPLS Module Installation and User Guide 3-11
MPLS Layer
The partitioning described in Table 3-3 maximizes forwarding performance, and
supports efficient load sharing of MPLS traffic across the Gigabit Ethernet backplane
links of high-speed input/output modules.
The data path uses the least significant 16 bits of the label (bits 0-15) as an index when a
label lookup is required. The next 2 bits of the label (bits 16-17) are currently not used
by the data path. The most significant 2 bits of the label (bits 18-19) are used to identify
the partition. The data path uses the label partition bits in conjunction with the
bottom-of-stack flag to efficiently determine how a label should be processed, as
described in Table 3-4.
The MPLS module does not limit the number of labels that can be popped by the egress
LSR function, as indicated in Table 3-4.
When the switch performs label swapping as a transit or intermediate LSR, no hard
limits are imposed on the maximum size of the label stack, other than the constraint of
not exceeding the maximum frame size supported by the physical links comprising the
LSP. You should enable jumbo frame support on the ports that are members of an MPLS
VLAN. The jumbo frame size should be set to accommodate the addition of a
Table 3-3: MPLS Label Space Partitions
Label Range Label Partition Description
x00000-x0000F Defined/reserved by MPLS standards specified in RFC 3032.
x00010-x0BBFF
(48,112) LSR Partition — Used to identify intermediate LSR LSPs.
x8C000-x8FFFF
(16,384) TLS LER Partition — Used to identify the VLAN for which TLS
traffic is destined when performing the egress LER function.
xCBC00-xCBFFF
(1024) IP LER Partition — Used for mappings to IP FECs when
performing the egress LER function.
Table 3-4: Label Processing by the NP Data Path
Partition Bottom-of-stack Label Processing
LSR Don’t Care Perform label lookup.
IP Yes Remove MPLS header and perform normal IP
forwarding.
TLS Yes Remove MPLS header and parse encapsulated
Ethernet frame as if it were received.
IP or TLS No Pop the label and repeat processing on the next label.