Alcatel-Lucent 7750 SR OS - LDP ECMP Tree Building

OAM Overview
Page 1380 7750 SR OS Services Guide
g. Users can configure the values to write into the DSCP and the EXP fields of the LSP
trace messages such that they get queued in the proper forwarding class queue in the
network.
h. The processing of the LSP trace packets does not cause critical CPM/IOM tasks (for
example, routing re-convergence) to be delayed.
2. A periodic path exercising capability to check the continuity of the discovered paths.
a. The continuity check tool uses LSP ping probes.
b. This tool can run periodically at a frequency of at least 1 probe per minute per discovered
FEC path.
c. The processing of the probe messages does not cause critical CPM/IOM tasks (for
example, routing re-convergence) to be delayed.
d. The ingress PE to can generate SNMP based alarms to the OSS layer to indicate faults
conditions and clearing of faults. Note that failures which the network has recovered from
does not cause alarms.
e. The alarms generated contain sufficient information to allow an OSS to localize the
faulty node/link and to identify the service/customers impacted by the fault.
LDP ECMP Tree Building
The 7750 SR ingress LER builds the ECM tree for a given FEC (egress LER) by sending LSP
trace messages and including the LDP IPv4 Prefix FEC TLV as well as the downstream mapping
TLV.In order to build the ECMP tree, the 7750 SR LER inserts an IP address range drawn from the
127/8 space. When received by the downstream LSR, it will use this range to determine which
ECMP path is exercised by any IP address or a sub-range of addresses within that range based on
its internal hash routine. When the MPLS echo reply is received by the 7750 SR LER, it will
record this information and proceed with the next echo request message targeted for a node
downstream of the first LSR node along one of the ECMP paths. The sub-range of IP addresses
indicated in the initial reply will be used since the objective is to have the LSR downstream of the
7750 SR LER pass this message to its downstream node along the first ECMP path.
The following figure illustrates the behavior through the following example adapted from RFC
4379, Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures:
PE1 ---- A ----- B ----- C ------ G ----- H ---- PE2
\ \---- D ------/ /
\ \--- E------/ /
-- F --------------------/