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Chapter 11
Troubleshooting Switched Ethernet
F I G U R E 1 1 . 2
The ISL encapsulation
Figure 11.2 is indexed in Table 11.4.
T A B L E 1 1 . 4
Key for Figure 11.2
Figure Symbol
Definition
ISL multicast address
The ISL multicast address of
01:00:0C:00:00. Note that this is a
40-bit value.
Type code
The encapsulated frame's type
code. For Ethernet, this is 0000. To-
ken Ring frames are defined with
0001 and FDDI is marked with 0010.
ATM has been reserved for 0011 as
a type code.
User bits
The user-defined bits are used to
mark the encapsulated frame's pri-
ority. Frames marked 0000 are pro-
cessed as normal priority, whereas
0011 marks the frame as high prior-
ity.
Source address
This is the 48-bit MAC address of
the source port.
8
16
24
32
ISL multicast
Source
User bits
Type code
Address
Address
Original frame (up to 24,575 octets)
Reserved
Index
VLAN ID and Bridge bit
Length
Binary
Expression
Organization ID
ISL CRC
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