1Q
Trunk
802.1Q
Trunk
Catalyst
Series Switch
Catalyst
Series Switch
VLAN 1
VLAN 2 VLAN 3 VLAN 1 VLAN 2
VLAN 3
26 Chapter 2: Medium-Sized Switched Network Construction
Figure 2-9 802.1Q Frame Format
802.1Q Native VLAN
An 802.1Q trunk and its associated trunk ports have a native VLAN value. 802.1Q does not
tag frames for the native VLAN. Therefore, ordinary stations can read the native untagged
frames but cannot read any other frame because the frames are tagged. Figure 2-10 shows
a frame from the native VLAN being distributed across the network trunks untagged.
Figure 2-10 Untagged Frame
Understanding VLAN Trunking Protocol
VLAN Trunking Protocol (VTP) is a Layer 2 messaging protocol that maintains VLAN
con?¬?guration consistency by managing the additions, deletions, and name changes of
VLANs across networks. VTP minimizes miscon?¬?gurations and con?¬?guration
Ether Type (0x8100) PRI VLAN ID
Token Ring Encapsulation Flag
Destination Source Length/Ether Type Data FCS Original Frame
Destination Source Tag Length/Ether Type Data FCS Tagged Frame
802.1Q
Trunk
802.1Q
Trunk
802.1Q
Trunk
802.1Q
Trunk
VLAN 1
VLAN 2 VLAN 3
VLAN 1
VLAN 1 VLAN 2
VLAN 3
Native VLAN??“Untagged
Implementing VLANs and Trunks 27
inconsistencies that can cause problems, such as duplicate VLAN names or incorrect
VLAN-type speci?¬?cations.
Pages:
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61