Periodic Path Exercising - Alcatel-Lucent 7750 SR OS Service Manual

OAM and SAA
LSR A has two downstream LSRs, B and F, for PE2 FEC. PE1 receives an echo reply from A with
the Multipath Type set to 4, with low/high IP addresses of 127.1.1.1->127.1.1.255 for downstream
LSR B and 127.2.1.1->127.2.1.255 for downstream LSR F. PE1 reflects this information to LSR
B. B, which has three downstream LSRs, C, D, and E, computes that 127.1.1.1->127.1.1.127
would go to C and 127.1.1.128-> 127.1.1.255 would go to D. B would then respond with 3
Downstream Mappings: to C, with Multipath Type 4 (127.1.1.1->127.1.1.127); to D, with
Multipath Type 4 (127.1.1.127->127.1.1.255); and to E, with Multipath Type 0.
The 7750 SR supports multipath type 0 and 8, and up to a maximum of 36 bytes for the multipath
length and supports the LER part of the LDP ECMP tree building feature.
A user configurable parameter sets the frequency of running the tree trace capability. The
minimum and default value is 60 minutes and the increment is 1 hour.
The 7750 SR LER gets the list of FECs from the LDP FEC database. New FECs will be added to
the discovery list at the next tree trace and not when they are learned and added into the FEC
database. The maximum number of FECs to be discovered with the tree building feature is limited
to 500. The user can configure FECs to exclude the use of a policy profile.

Periodic Path Exercising

The periodic path exercising runs in the background to test the LDP ECMP paths discovered by
the tree building capability. The probe used is an LSP ping message with an IP address drawn
from the sub-range of 127/8 addresses indicated by the output of the tree trace for this FEC.
The periodic LSP ping messages continuously probes an ECMP path at a user configurable rate of
at least 1 message per minute. This is the minimum and default value. The increment is 1 minute.
If an interface is down on a 7750 SR LER, then LSP ping probes that normally go out this
interface will not be sent.
The LSP ping routine updates the content of the MPLS echo request message, specifically the IP
address, as soon as the LDP ECMP tree trace has output the results of a new computation for the
path in question.
7750 SR OS Services Guide Page 1381