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16-4
Cisco ASR 1000 Series Aggregation Services Routers Software Configuration Guide
OL-16506-17
Chapter 16 Configuring MPLS Layer 2 VPNs
Virtual Private LAN Services
In routed interworking, the IP packets that are extracted from the ACs are sent over the pseudowire. The
pseudowire works in the IP Layer 2 transport (VC type 0x000B) like-to-like mode. The interworking
function at the network service provider's (NSP) end completes the required adaptation based on the AC
technology. The non-IPv4 packets are dropped.
In routed interworking, the following considerations must be kept in mind:
• ARP, inverse ARP, and IPCP are punted to the routing protocol.
Therefore, the PE router at the NSP end must provide the following address-resolution
functionalities for the Ethernet and ATM and Frame Relay point-to-point subinterface attachment
circuits:
–
Ethernet—The PE device acts as a Proxy ARP server to all the ARP requests from the CE router.
The PE router responds with the MAC address of its local interface.
–
ATM and Frame Relay point-to-point subinterface—By default, inverse ARP does not run in the
point-to-point Frame Relay or ATM subinterfaces. The IP address and subnet mask define the
connected prefix; therefore, configuration is not required in the CE devices.
• Interworking requires that the MTUs in both the ACs must match for the pseudowire that is to come
up. The default MTU in one AC must match the MTU of other AC.
Table 16-1 lists the range of MTUs that can be configured for different ACs.
• The CE routers with Ethernet attachment VCs running OSPF must be configured with the ospfIfType
option so that the OSPF protocol treats the underlying physical broadcast link as a P2P link.
Virtual Private LAN Services
Virtual Private LAN Service (VPLS) enables enterprises to link together their Ethernet-based LANs
from multiple sites via the infrastructure provided by their service provider. From the enterprise
perspective, the service provider's public network looks like one giant Ethernet LAN. For the service
provider, VPLS provides an opportunity to deploy another revenue-generating service on top of their
existing network without major capital expenditures. Operators can extend the operational life of
equipment in their network.
Virtual Private LAN Services (VPLS) uses the provider core to join multiple attachment circuits together
to simulate a virtual bridge that connects the multiple attachment circuits together. From a customer
point of view, there is no topology for VPLS. All of the CE devices appear to connect to a logical bridge
emulated by the provider core.
Table 16-1 Range of MTUs for Different ACs
AC Type Range of MTUs
1
Supported
1. The MTU configured on an AC must not exceed the MTU in the core network. This ensures that the traffic is not fragmented.
ATM 64 to 9216
Gigabit Ethernet 1500 to 9216
POS 64 to 9216
Fast Ethernet 1500 to 9216