What is the purpose of frame tagging in Virtual LAN (VLAN) configurations?
A.
inter-VLAN routing
B.
encryption of network packets
C.
frame identification over trunk links
D.
frame identification over access links
Explanation:
Frame tagging is used when VLAN traffic travels over a trunk link. Trunk links carry frames for multiple VLANs.Therefore, frame tags are used for identification of frames from different VLANs. Inter Switch Link (ISL) and
Institute of Electrical and Electronics Engineers (IEEE) 802.1q are the two frame tagging methods supported on
Cisco devices.
The purpose of frame tagging is not inter-VLAN routing. A Layer 3 device, such as a router or multilayer switch,
is used for inter-VLAN routing. To configure inter-VLAN routing a logical or subinterface for each VLAN must be
created on the single physical interface used to connect to the switch. An IP address is NOT applied to the
physical interface; instead, each subinterface is configured with an IP address that will become the default
gateway of all devices residing in that VLAN. Consequently, each subinterface and its VLAN devices must
reside a different subnet as well. If a subinterface on the router is NOT configured with an IP address that
resides in the same network as the hosts that reside in the VLAN that the subinterface serves, the hosts in that
VLAN will be isolated from the other VLANs. The hosts in the VLAN served by the subinterface should also use
this address as their default gateway, or the hosts in the VLAN will likewise be isolated form the other VLANs
To verify the IP address of the subinterface, execute the show interfaces subinterface ID command. As shown
below, the IP address will appear in line 3 of the output. Compare this IP address will the IP address set as the
default gateway of each host in the VLAN served by the subinterface. They should be the same, and the IP
address of the hosts should be in the same subnet as this address as well.
router# show interfaces fastEthernet 0/0.1
FastEthernet0/0.1 is up, line protocol is up
Hardware is AmdFE, address is 0003.e36f.41e0 (bia 0003.e36f.41e0)
Internet address is 10.10.10.1/24
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ISL Virtual LAN, Color 1.
ARP type: ARPA, ARP Timeout 04:00:00
Frame tagging does not provide encryption of network packets. Packets are transmitted unencrypted unless the
network device or the application uses an additional encryption mechanism. A Virtual Private Network (VPN) is
a popular solution for providing encrypted network communication.
An access link is a connection between a switch and an end-user computer with a normal Ethernet Network
Interface Card (NIC). On these links, Ethernet frames are transmitted without frame tagging.
Objective:
LAN Switching Fundamentals
Sub-Objective:
Configure, verify, and troubleshoot VLANs (normal/extended range) spanning multiple switchesCisco > Cisco IOS LAN Switching Configuration Guide, Release 12.4 > Part 1: Virtual LANs > Routing Between
VLANs Overview
Cisco > Technology Support > LAN Switching > Virtual LANs/VLAN Trunking Protocol (VLANs/VTP) > Design >
Design Technotes > Inter-Switch Link and IEEE 802.1Q Frame Format > Document ID: 17056