A BFD session on an LSP is bootstrapped using LSP ping. LSP ping is used to exchange the local and remote discriminator values to use for the BFD session for a specific MPLS LSP or FEC.
The process for bootstrapping an LSP BFD session for LDP is the same as for RSVP, as described in Bidirectional Forwarding Detection for MPLS LSPs.
SR OS supports the sending of periodic LSP ping messages on an LSP for which LSP BFD has been configured, as specified in RFC 5884. The ping messages are sent, along with the bootstrap TLV, at a configurable interval for LSPs where bfd-enable is configured. The default interval is 60 s, with a maximum interval of 300 s. The LSP ping echo request message uses the system IP address as the default source address. An alternative source address consisting of any routable address that is local to the node may be configured and used if the local system IP address is not routable from the far-end node.
SR OS does not take any action if a remote system fails to respond to a periodic LSP ping message. However, when the show>test-oam>lsp-bfd command is executed, it displays a return code of zero and a replying node address of 0.0.0.0 if the periodic LSP ping times out.
The periodic LSP ping interval is configured using the config>router>ldp>lsp-bfd prefix-list>lsp-ping-interval seconds command.
Configuring an LSP ping interval of 0 disables periodic LSP ping for LDP FECs matching the specified prefix list. The no lsp-ping-interval command reverts to the default of 60 s.
LSP BFD sessions are recreated after a high-availability switchover between active and standby CPMs. However, some disruption may occur to LSP ping as a result LSP BFD.
At the head end of an LSP, sessions are bootstrapped if the local and remote discriminators are not known. The sessions experience jitter at 0 to 25% of a retry time of 5 seconds. A side effect of the bootstrapping is that the following current information is lost from an active show test-oam lsp-bfd display:
Replying Node
Latest Return Code
Latest Return SubCode
Bootstrap Retry Count
Tx Lsp Ping Requests
Rx Lsp Ping Replies
If the local and remote discriminators are known, the system immediately begins generating periodic LSP pings. The pings experience jitter at 0 to 25% of the lsp-ping-interval time of 60 to 300 seconds. The lsp-ping-interval time is synchronized across by LSP BFD. A side effect of the bootstrapping is that the following current information is lost from an active show test-oam lsp-bfd display:
Replying Node
Latest Return Code
Latest Return SubCode
Bootstrap Retry Count
Tx Lsp Ping Requests
Rx Lsp Ping Replies
At the tail end of an LSP, sessions are recreated on the standby CPM following a switchover. The side effect of this is that the following current information is lost from an active tools dump test-oam lsp-bfd tail display:
handle
seqNum
rc
rsc
New, incoming bootstrap requests are dropped until the LSP BFD session is active. When the LSP BFD session is active, new bootstrap requests are considered.