LSP ping and LSP traceroute are supported on BGP route tunnels using existing LSP ping and traceroute commands with the bgp-label prefix option. The system uses the DSMAP TLV target FEC stack TLV for BGP-labeled IPv4 /32 prefix as defined in RFC 4379, Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures. Figure: Target FEC Stack TLV for BGP-Labeled IPv4 Prefix shows the new TLV structure.
The following process is used when sending or responding to an LSP ping or LSP traceroute packet on BGP route tunnels.
The next hop of a BGP-labeled route for a core IPv4 /32 prefix is always resolved to an LDP FEC or an RSVP-TE LSP. The transmitting node encapsulates the packet containing the echo request message with a label stack that consists of the LDP/RSVP-TE outer label and the BGP inner label.
If the packet expires on an RSVP-TE or LDP LSR node that does not have context for the BGP-labeled IPv4 /32 prefix, the system must validate the outer label in the stack, and if the validation is successful, it must reply with return code 8 <Label switched at stack-depth <RSC>>.
An LSR node that is the next hop for the BGP-labeled IPv4 /32 prefix, as well as the LER node that originated the BGP-labeled IPv4 prefix, have full context for the BGP IPv4 target FEC stack and can therefore perform full validation of it.
The 7705 SAR supports only BGP-labeled IPv4 /32 prefixes in LSP ping and LSP trace.
For more information about BGP route tunnels, see the 7705 SAR Routing Protocols Guide, "BGP Route Tunnels".