Dell PowerConnect J-8216 Software Guide for JUNOS version 10.3 - Page 1123

Chapter 57: Bridging and VLANs-Overview Link 1 is down between Switch 3 and Switch 1. Link 2 takes over as the active link. Traffic between the access layer and the distribution layer is automatically switched to Link 2 between Switch 1 and Switch 2. Related • Example: Configuring Redundant Trunk Links for Faster Recovery on page 1101 Documentation • redundant-trunk-group on page 1218 Understanding Q-in-Q Tunneling on J-EX Series Switches Q-in-Q tunneling allows service providers on Ethernet access networks to extend a Layer 2 Ethernet connection between two customer sites. Using Q-in-Q tunneling, providers can also segregate or bundle customer traffic into fewer VLANs or different VLANs by adding another layer of 802.1Q tags. Q-in-Q tunneling is useful when customers have overlapping VLAN IDs, because the customer's 802.1Q (dot1Q) VLAN tags are prepended by the service VLAN (S-VLAN) tag. The Junos OS implementation of Q-in-Q tunneling supports the IEEE 802.1ad standard. This topic describes: • How Q-in-Q Tunneling Works on page 1051 • Disabling MAC Address Learning on page 1052 • Mapping C-VLANs to S-VLANs on page 1052 • Routed VLAN Interfaces on Q-in-Q VLANs on page 1053 • Limitations for Q-in-Q Tunneling on page 1054 How Q-in-Q Tunneling Works In Q-in-Q tunneling, as a packet travels from a customer VLAN (C-VLAN) to a service provider's VLAN, a customer-specific 802.1Q tag is added to the packet. This additional tag is used to segregate traffic into service-provider-defined service VLANs (S-VLANs). The original customer 802.1Q tag of the packet remains and is transmitted transparently, passing through the service provider's network. As the packet leaves the S-VLAN in the downstream direction, the extra 802.1Q tag is removed. When Q-in-Q tunneling is enabled on J-EX Series Switches, trunk interfaces are assumed to be part of the service provider network and access interfaces are assumed to be customer facing. An access interface can receive both tagged and untagged frames in this case. An interface can be a member of multiple S-VLANs. You can map one C-VLAN to one S-VLAN (1:1) or multiple C-VLANs to one S-VLAN (N:1). Packets are double-tagged for an additional layer of segregating or bundling of C-VLANs. C-VLAN and S-VLAN tags are unique; so you can have both a C-VLAN 101 and an S-VLAN 101, for example. You can limit the set of accepted customer tags to a range of tags or to discrete values. Class-of-service (CoS) values of C-VLANs are unchanged in the downstream direction. You may, optionally, copy ingress priority and CoS settings to the S-VLAN. Using private VLANs, you can isolate users to prevent the forwarding of traffic between user interfaces even if the interfaces are on the same VLAN. 1051