Cisco 3845 Software Guide - Page 824

Understanding MPLS OAM Chapter 34 Configuring MPLS, MPLS VPN, MPLS OAM, and EoMPLS 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. AToM VCCV (LSP Ping over Pseudowire) You can use AToM VCCV control words to send control packets inband of an AToM pseudowire from the originating provider edge router or out-of-band by using router alert. The switch supports out-of-band VCCV. You configure this by using the ping mpls pseudowire privileged EXEC command. The transmission is intercepted at the destination provider-edge router, instead of being forwarded to the customer-edge router. You can use AToM VCCV and MPLS LSP ping to test the pseudowire section of AToM virtual circuits. AToM VCCV consists of these components: • A signaled component in which the AToM VCCV capabilities are advertised during virtual-circuit label signaling • A switching component that causes the AToM VC payload to be treated as a control packet An LSP ping through a Layer 2 pseudowire requires that the originating router first validate the pseudowire control channel capability during the exchange of virtual-circuit labels. In the switch, this is done by using a router alert label, which sends the LSP ping or traceroute packet to the egress PE router processor instead forwarding it to the CE devices. This is type 2 AToM VCCV. The switch does not support inband VCCV validation using a control word (type 1). IP SLAs Interworking with MPLS OAM IP SLAs provides a way to generate MPLS LSPs and measure statistics between provider-edge routers participating in the MPLS network. It uses LSP ping and traceroute to determine network availability or measure network connectivity and performance between the provider-edge routers. You can manually configure IP SLAs LSP ping or traceroute, or you can configure it using the IP SLAs Health Monitor. • When you manually configure LSP ping or traceroute, you explicitly specify the FEC you want to validate, for example, a VPN end point. • When you use the MPLS LSP Health Monitor, you specify a VRF, and the monitor automatically discovers the VPN end points. When configured, the LSP Health Monitor automatically creates and deletes IP SLAs LSP ping or LSP traceroute operations based on network topology. It automatically discovers all adjacent BGP next-hop provider-edge routers and creates individual IP SLAs LSP ping operations for each applicable BGP next-hop neighbor. For more information on configuring the LSP Health Monitor, go to this URL: http://www.cisco.com/en/US/docs/ios/ipsla/configuration/guide/sla_lsp_mon_autodisc.html 34-44 Cisco ME 3800X and 3600X Switch Software Configuration Guide OL-23400-01