Pseudowire Headend - Cisco CRS Configuration Manual

Implementing Multipoint Layer 2 Services
It is recommended to enable pseudowire status time length value (TLV) for optimal switchover performance.
This feature is supported only for an AToM instance on the Cisco XR 12000 Series Router, and for an
Note
EoMPLS instance on the Cisco CRS-1 router.

Pseudowire Headend

Pseudowires (PWs) enable payloads to be transparently carried across IP/MPLS packet-switched networks
(PSNs). PWs are regarded as simple and manageable lightweight tunnels for returning customer traffic into
core networks. Service providers are now extending PW connectivity into the access and aggregation regions
of their networks.
Pseudowire Headend (PWHE) is a technology that allows termination of access pseudowires (PWs) into a
Layer 3 (VRF or global) domain or into a Layer 2 domain. PWs provide an easy and scalable mechanism for
tunneling customer traffic into a common IP/MPLS network infrastructure. PWHE allows customers to
provision features such as QOS access lists (ACL), L3VPN on a per PWHE interface basis, on a service
Provider Edge (PE) router.
PWHE cross-connects to a pseudowire neighbour, which is reachable through recursive as well as non-recursive
prefix. The reachability through recursive prefix is through introduction of BGP RFC3107 support on the
Cisco CRS Router. Consider the following network topology for an example scenario.
Figure 19: Pseudowire Network
For PWHE x-connect configuration, interconnectivity between A-PE (Access Provider Edge) and S-PE is
through BGP RFC3107 that distributes MPLS labels along with IP prefixes. The customer network can avoid
using an IGP to provide connectivity to the S-PE device, which is outside the customer's autonomous system.
For all practical purposes, the PWHE interface is treated like any other existing L3 interface. PWs operate in
one of the following modes:
• Bridged interworking (VC type 5 or VC type 4)
• IP interworking mode (VC type 11)
With VC type 4 and VC type 5, PWs carry customer Ethernet frames (tagged or untagged) with IP payload.
Thus, an S-PE device must perform ARP resolution for customer IP addresses learned over the PWHE. With
VC type 4 (VLAN tagged) and VC type 5 (Ethernet port/raw), PWHE acts as a broadcast interface. Whereas
with VC type 11 (IP Interworking), PWHE acts as a point-to-point interface. Therefore there are two types
of PWHE interface—PW-Ether (for VC type 4 and 5) and PW-IW (for VC type 11). These PWs can terminate
into a VRF or the IP global table on S-PE.
Cisco IOS XR Virtual Private Network Configuration Guide for the Cisco CRS Router, Release 6.1.x
Pseudowire Headend
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