Configuring Mpls OAM, LSP Traceroute, 17-2

Chapter 17 Configuring MPLS OAM

Configuring MPLS OAM

In response to an MPLS echo request, an MPLS echo reply is forwarded as an IP packet by using IP, MPLS, or a combination of both. The source address of the MPLS echo-reply packet is an address obtained from the router generating the echo reply. The destination address is the source address of the router that originated the MPLS echo-request packet. The MPLS echo-reply destination port is the echo-request source port.

LSP Traceroute

MPLS LSP traceroute also uses MPLS echo request and reply packets to validate an LSP. You can use MPLS LSP traceroute to validate LDP IPv4 by using the trace mpls privileged EXEC command. The traceroute time-to-live (TTL) settings force expiration of the TTL along an LSP. MPLS LSP traceroute incrementally increases the TTL value in its MPLS echo requests (TTL = 1, 2, 3, 4) to discover the downstream mapping of each successive hop. The transit router processing the MPLS echo request returns an MPLS echo reply containing information about the transit hop in response to the TTL-expired MPLS packet. The MPLS echo reply destination port is sent to the echo request source port.

LSP Ping over Pseudowire

The LSP Ping over Pseudowire is used for detecting faults in the data plane or forwarding path for pseudowire services. The connectivity verification model for pseudowires consists of:

•Advertising the VCCV capability

•Verifying the data plane connectivity

Advertising the VCCV capability is done as part of MPLS Label Mapping message. This consists of Control Channel (CC) type which is a bitmask that indicates the type of control channel that can be used to verify connectivity. The Cisco ASR 901 router supports the following CC type:

•MPLS Router Alert Label (Type 2) : The control channel is created out of band and uses the router alert label (RA).

Note The Cisco ASR 901 router does not support Control Channel Type 1 and 3.

Connectivity verification type defines a bitmask that indicates the types of CV packets and protocols that can be sent on the specified control channel.

The LSP ping over pseudowire uses the same label stack as used by the pseudowire data path. Basically it contains the virtual circuit (VC) label and tunnel labels.