of the ISL frame minus the multi-
cast address, the type and user-de-
fined bits, and the source address
of the ISL packet. The length field
also omits its own length and the
CRC from the 16-bit value. Thus, the
length is always equal to the length
of the ISL frame minus 18 octets.
binary expression noted in the table
above decodes to AA:AA:03, which
is the same as the SNAP header.
the unique organization identifier of
the source address. This is equal to
the first three octets of the MAC ad-
dress.
that identifies the VLAN member-
ship of the frame. Cisco uses only
10 bits in this header to support up
to 1,024 virtual LANs. The bridge bit
is set for all encapsulated bridge
protocol frames, including span-
ning tree updates, in addition to
Cisco's CDP and VTP (VLAN Trunk-
ing Protocol) packets.
troubleshooting and contains the
source port value of the frame.