cisco ccna quora

cisco ccna quora.Figure 1-29 Enabling VLANs and VLANTrunk in a Topology Consisting of Multiple SwitchesIn the network shown in Figure 1.29, Hosts A and E are directly connected to two different switches, but they can still be configured to belong to the same VLAN (for example, VLAN 101). o The interconnecting link between SW1 and SW2 is called a trunk link, which is a special link that can be used to pass frames belonging to multiple VLANs.To allow communication between hosts A and E, which belong to the same VLAN but are directly connected to two separate switches, you have to resort to VLAN tagging. As shown in Figure 1.29, when Host A sends a frame to E, SW1 does not know which of its ports is connected to Host E and will send the frame out through all ports belonging to VLAN 101, including the Trunk port connected to SW2.As the reader can see, SW1 does not forward the frame to host B, which belongs to another VLAN0 Before sending the frame over the Trunk link to SW2, SW1 adds a VLAN tag containing the VLANID (VLAN 101) to the frame, thereby informing SW1 of the VLAN tag.SW1 adds a VLAN tag containing the VLANID (VLAN 101) to the frame to inform SW2 that the frame should only be sent outbound from the port belonging to VLAN 101.When the frame is received over the trunk link, SW2 strips the VLAN tag and sends the frame out of all ports belonging to VLAN 101 (for this example, only out of F0/1). If Host E decides to send a frame in response to Host A, the same process applies. At this point, theSW2 will only send the frame out the Trunk link (because SW2 has already learned the MAC address of Host A from the Trunk port) and add a VLAN tag containing VLAN 101 to the frame.Adding VLAN information to an Ethernet frame relies on a protocol called VLAN Trunk. Today, the better known and more commonly used VLANTrunk protocol is defined in the IEEE802. Another VLANTrunk protocol is the Inter-Switch Link (ISL) protocol, a Cisco private protocol that was often used in the past.According to the IEEE 802.1Q standard, the specific way to add VLAN tags to an Ethernet frame is to add an IEEE802.1Q tag field between the source MAC address field and the type field of the Ethernet frame.Figure 1.30 shows the format of the IEEE802.1Q tag and its location in the Ethernet frame. The tag contains the frame's VLAN IDO