BSR 2000 Configuration and Management Guide
Release 1.0
13-4
MGBI
526360-001-00 Rev. B
Each enterprise requires a "per-Enterprise" VLAN implemented on the L2/L3
backbone. In addition, each cable modem configured for bridging requires a
"per-CM" VLAN on the connection between the L2/L3 switch and the BSR. The L2/
L3 switch performs inter-VLAN bridging of the per-CM VLANs together into the
per-Enterprise VLAN. The Ethernet connection between the L2/L3 switch and the
BSR is configured as an IEEE 802.1Q "trunk" mode port, which tags all Ethernet
packets with a particular VLAN number.
When the BSR forwards bridged packets to the L2/L3 switch, it always indicates a
particular VLAN for the bridged packet using 802.1Q tags. When the BSR forwards
an IP routed packet, however, it may or may not be tagged, depending on BSR
configuration.
VLAN Tagging Packet Formats
On the BSR Ethernet interface, separate VLANs are identified with a tag as defined
by the IEEE 802.1Q standard.
The IEEE 802.1Q standard defines a format for adding 4 additional bytes to Ethernet
packets to identify the packet as belonging to a particular VLAN. The original
two-byte Ethernet Type field is replaced by the special type code 0x8100, followed
by a 16-bit VLAN ID tag. The VLAN ID Tag field contains 12 bits that define the
VLAN ID number for the packet. The original Ethertype field then follows the VLAN
ID field. The operation of 802.1Q Tagging is depicted In Figure 1-2.
Figure 13-2 IEEE 802.1Q VLAN Tagging
Original CPE Ethernet Packet
IEEE 802.1Q VLAN Tagged Ethernet Packet
DA(6)
SA(6)
Original
Type (2)
Data (1500
bytes maximum)
DA(6)
SA(6)
0x8100
VLAN ID
Tag (2)
Original
Type (2)
Data (1500
bytes maximum)
Содержание BSR 2000
Страница 1: ...BSR 2000 Configuration and Management Guide 526360 001 00 Rev B Release 1 0 MGBI ...
Страница 6: ... Motorola Motorola Motorola Motorola Motorola Motorola Motorola Motorola Motorola ...
Страница 50: ......
Страница 130: ......
Страница 164: ......
Страница 458: ......
Страница 490: ......
Страница 580: ......
Страница 632: ......
Страница 648: ......
Страница 649: ......
Страница 650: ...526360 001 00 Rev B 7 06 MGBI Visit our website at www motorola com ...