Assume that an enterprise uses different VLANs to identify services. They communicate with each other across the carrier network using the public VLAN 3. When a user connected to CE1 sends a packet to a user connected to CE When a user connected to CE3 needs to communicate with a user connected to CE1, the same process is implemented in reverse.
It, however, requires an extra packet overhead, that is, an additional VLAN tag. After the packets arrive at the edge device connected to the destination user network, the edge device retrieves the C-VLAN ID to ensure seamless interworking between the two user networks. This means the two networks can be managed as a single Layer 2 network, while it helps implement Layer 2 user communication and unified deployment of Layer 2 protocols.
All rights reserved. Your browser does not support the video tag. What Is This is stressed because a lot of people think that it's the other way around, meaning, a switch's uplink is always a Trunk Link and any normal port where you would usually connect a workstation, is an Access Link port! We're now familiar with the term 'Trunk Link' and its purpose, that is, to allow frames from multiple VLANs to run across the network backbone, finding their way to their destination.
What you might not have known though is that there is more than one method to 'tag' these frames as they run through the Trunk Links or The protocol can be used in various equipments such as switch ports, router interfaces, server interface cards to create a trunk to a server and much more.
Being a propriety protocol, ISL is available and supported naturally on Cisco products only: You may also be interested in knowing that ISL is what we call, an 'external tagging process'. This means that the protocol does not alter the Ethernet frame as shown above in our previous diagram - placing the VLAN Tag inside the Ethernet frame, but encapsulating the Ethernet frame with a new 26 byte ISL header and adding an additional 4 byte frame check sequence FCS field at the end of frame, as illustrated below:.
This is the actual frame that runs through a trunk link between two Cisco devices when configured to use ISL as their trunk tagging protocol. The encapsulation method mentioned above also happens to be the reason why only ISL-aware devices are able to read it, and because of the addition of an ISL header and FCS field, the frame can end up being bytes long!
For those who can't remember, Ethernet's maximum frame size is bytes, making an ISL frame of bytes, what we call a 'giant' or 'jumbo' frame! This method allows us to optimise the root switch placement for each available VLAN while supporting neat features such as VLAN load balancing between multiple trunks. Since the ISL's header fields are covered on a separate page, we won't provide further details here.
The On an EX switch, you can configure multiple logical interfaces on the same Ethernet port, but each logical interface supports only single-tagged packets and that tag must include a different VLAN ID than those supported by the other logical interfaces. Given this situation, you cannot enable Q-in-Q tunneling on Ethernet ports with multiple logical subinterfaces.
Depending on your interface configuration, you might need to adjust the MTU value on your trunk or access ports to accommodate the 4 bytes used for the tag added by Q-in-Q tunneling. For example, if you use the default MTU value of bytes on your access and trunk ports, you need to make one of the following adjustments:.
To configure VLAN translation, use the mapping swap statement at the [edit vlans interface] hierarchy level. If you are translating more than one VLAN, you must use the dot1q-tunneling statement.
You can configure VLAN translation on access ports only. You cannot configure it on trunk ports, and you cannot configure Q-in-Q tunneling on the same access port. Starting with Junos OS Release Table 1 shows the operations that are added for dual VLAN tag translation. To enable an interface to send and receive untagged packets, you must specify a native VLAN for a physical interface. When the switches in the short list above receive an untagged packet, they add the S-VLAN tag to the packet so the packet is single-tagged and send the newly tagged packet to the mapped interface.
Ensure that all switches configured in your Q-in-Q setup operate with either the single-tag approach or the double-tag approach. The setup will not work if the switches do not have the same approach. Starting in Junos OS Release Set the configuration statement input-native-vlan-push to enable and ensure that the input-vlan-map configuration statement is set to push , as shown in the following example:. On switches that support this feature, except for the EX switch, the input-native-vlan-push statement is set to enable by default.
The input-native-vlan-push statement is set to disable by default on the EX switch. To specify a native VLAN, use the native-vlan-id statement at the [edit interfaces interface-name ] hierarchy level. In a Q-in-Q deployment, customer packets from downstream interfaces are transported without any changes to source and destination MAC addresses. This results in routed packets flooding all the interfaces associated with the VLAN.
If you configure multiple mapping methods, the switch gives priority to mapping a specific interface, then to many-to-many bundling, and last to all-in-one bundling. However, for a particular mapping method, setting up overlapping rules for the same C-VLAN is not supported. All-in-one bundling—Use the edit vlans s-vlan-name dot1q-tunneling statement without specifying customer VLANs.
If you want untagged or priority tagged packets to be mapped to the S-VLAN, use the native option with the customer-vlans statement.
This configuration applies to only one interface—not all access interfaces as with all-in-one and many-to-one bundling. This method has two options: swap and push. With the push option, a packet retains its tag and an additional VLAN tag is added. This is VLAN translation.
This functionality is typically used to keep traffic from different customers separate or to provide individualized treatment for traffic on a certain interface. Page: Required: page refresh 5. Snom Service Hub. Space shortcuts Firmware Archive. Child pages. Browse pages. A t tachments 2 Page History People who can view.
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