Riverstone Networks WICT1-12 - Manual (Page 368)

17-60 Riverstone Networks RS Switch Router User Guide Release 8.0
Configuring L2 Tunnels MPLS Configuration
17.6 CONFIGURING L2 TUNNELS
Riverstone’s layer-2 (L2) MPLS implementation supports the encapsulation and transport of L2 Protocol Data Units
(PDUs) across an MPLS network, as described in the Martini Internet-Draft. This feature allows you to use MPLS
labels, instead of network layer encapsulation, to tunnel L2 frames across a backbone MPLS network. For metro
service providers, this has many important benefits:
• Scalability of 802.1q and IP VPN services. With 802.1q VLANs, the total number of VLANs in the
entire network is limited to 4,096. With IP VPNs, layer-2 tunnel protocol (L2TP) tunnels that carry
traffic across the MPLS network must be manually configured with a pair of IP addresses assigned
to each tunnel. With MPLS, packets to be sent through the L2 tunnel can be considered as a single
FEC. Transit LSRs only need to look at the top label to switch the labeled packet across the MPLS
network.
• L2 tunnels across backbone networks can be added as virtual interfaces to VLANs, allowing
transparent bridging across the backbone. Customer network information, such as MAC addresses
and VLAN IDs, is not exposed to the backbone network since only the outer MPLS label is
examined by each router in the tunnel.
• Many end-to-end customer-specific or VLAN-specific virtual circuits can be bundled into a small
number of L2 tunnels that run through the backbone. Traffic on each virtual circuit is isolated from
each other, with the same level of security as a frame relay or ATM virtual circuit.
The RS supports two basic types of virtual circuit labels:
• Static labels require that you configure all routers and all labels in the path. MPLS must be enabled.
No signaling protocol is used, so you do not need to enable RSVP or LDP.
• Dynamic labels use LDP signaling on the ingress and egress LSRs to specify the FEC-to-label
mapping for the virtual circuit. You can use either RSVP or LDP signaling within the tunnel LSP.
Note The RS supports the transport of Ethernet frames only with MPLS labels.
17.6.1 Configuring L2 Static Labels
With L2 static labels, each router in the path must be configured with static forwarding information. No signaling
protocol is used. MPLS must be enabled on all routers, as described in
Section 17.2, "Enabling and Starting MPLS on
the RS."
Note Because each L2 LSP is unidirectional, you need to configure one LSP in each
direction to provide a bidirectional pipe. You do not need to configure the same
LSRs in each path.
For an L2 static LSP, the following criteria can be considered for the FEC-to-label binding:
• VLAN ID and source and/or destination MAC address
• VLAN ID and 802.1p priority
You configure a policy on the ingress LSR so that only frames that meet certain criteria, such as a specific VLAN ID
and source MAC address, are mapped to an FEC for forwarding on the LSP.