3Com 7757 Configuration Manual page 93

Procedure for the Switch
to Judge Packet Protocol
Encapsulation Formats
The switch differentiates between 802.2 LLC encapsulation and 802.3 SNAP
encapsulation according to the values of the DSAP field and the SSAP field.
n
When the OUI is 00-00-00 in 802.2 SNAP encapsulation, the PID field has the
same meaning as the type field in Ethernet II encapsulation, which both refer to
globally unique protocol number. Such encapsulation is also known as SNAP
RFC1042 encapsulation, which is standard SNAP encapsulation. The SNAP
encapsulation mentioned in this chapter refers to SNAP RFC 1042 encapsulation.
Figure 33 Procedure for the switch to judge packet protocol
Ethernet II Ethernet II
0x0600 to 0xFFFF 0x0600 to 0xFFFF
ncapsulation ncapsulation
Match the Match the
type value type value
802.3 raw 802.3 raw
encapsulation encapsulation
Table 45 Encapsulation formats
Encap Protocol
IP Supported Not
IPX Supported Supported Supported Supported 0x8137
AppleTalk Supported Not
Receive Receive
packets packets
Type(Length) Type(Length)
field field
0 to 0x05DC 0 to 0x05DC
802.2/802.3 802.2/802.3
encapsulation encapsulation
Control Control
field field
Value is 3 Value is 3
dsap/ssap dsap/ssap
Both are FF Both are FF
value value
Other values Other values
802.2 LLC 802.2 LLC
encapsulation encapsulation
Match the Match the
dsap/ssap value dsap/ssap value
Ethernet
II 802.3 raw 802.2 LLC
Not
supported supported
Not
supported supported
Protocol-Based VLAN
Invalid packets Invalid packets
that cannot be that cannot be
0x05DD to 0x05FF 0x05DD to 0x05FF
matched matched
Invalid packets Invalid packets
that cannot be that cannot be
Value is not 3 Value is not 3
matched matched
802.2 SNAP 802.2 SNAP
Both are AA Both are AA
encapsulation encapsulation
Match the Match the
type value type value
802.2
SNAP Type value
Supported 0x0800
Supported 0x809B
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