December 2005
Intermediate to advanced
1066 pages
33h 38m
English
Content preview from Understanding Linux Network Internals
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BPDU Encapsulation
The L2 multicast addresses in the range 01:80:C2:00:00:00 to 01:80:C2:00:00:FF are reserved by IEEE for standard protocols. In particular, the first address of the range, 01:80:C2:00:00:00, is used by the 802.1D STP: both configuration and TCN BPDUs are sent to this address. This address is what allows bridges to recognize BPDUs.
Figure 15-20 shows what the encapsulation of a BPDU inside an Ethernet frame looks like.
For more details on the LLC header, you can refer to Chapter 13.
Note that the same IEEE spec states that the addresses in the range 01:80:C2:00:00:00 to 01:80:C2:00:00:0F should not be relayed by a bridge running the 802.1D protocol: they are either processed locally by the destination protocol (if implemented and enabled) or dropped.
Figure 15-19. Notifying all bridges about the topology change
Figure 15-20. BPDU encapsulation
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