Configuring 802.1Q tunnneling (Q-in-Q) on Cisco switches

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cisco

Overview

The 802.1Q tunnneling technology also known as Q-in-Q is an extension to the well known 802.1Q standard which allows service providers to transport customers VLANs by simply adding another layer of IEEE 802.1Q tag to the original 802.1Q tagged packets that enter the ISP network. Customer VLAN IDs are preserved and traffic from different customers is segregated within the service-provider infrastructure even when they appear to be on the same VLAN. The primary benefit for the service provider is reduced number of VLANs supported for the same number of customers. By using 802.1Q tunneling the layer 2 domain of a customer can be extended across multiple sites. A Q-in-Q frame can be identified by the Ethertype field 0x8100 in the Ethernet header and it’s called a double-tagged frame. One outer ISP VLAN tag can carry 4096 customer VLAN tags and this brings the total number of available VLANs to approximately 16.8 million.

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Configuring Generic Routing Encapsulation (GRE) tunnels on Cisco IOS

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cisco

Overview

Generic routing encapsulation (GRE) is a tunneling protocol which was initially developed by Cisco, and later it has been adopted as an industry standard in RFC 2784. GRE allows the encapsulation of a wide variety of network layer protocols inside virtual point-to-point links. This means that the original packet is encapsulated inside a GRE header and a new IP header containing the source and the destination of the tunnel endpoints. The GRE protocol does not provide any security for the data being transported so if encryption is needed GRE must be used in conjunction with IPsec protocol. Some of the reasons for using GRE are the need to transport multicast traffic, or to provide workarounds for networks with limited hops. In this article we will demonstrate how two networks which do not have reachability can be connected through an GRE tunnel.

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