Hi,
This is the only thing I found that is defined as mandatory for ASR903 and note that this is for IS-IS (page 25)
Configuring IS-IS Remote Loop-Free Alternate Fast Reroute
The following additional configurations are mandatory:
• mpls ldp discovery targeted-hello accept
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_pi/configuration/xe-3s/asr903/iri-xe-3s-asr903-book.pdf
A brief explanation of the commands you specified
mpls ldp explicit-null -
this command used on penultimate router, the router swaps an MPLS label with a NULL label.
this command can be used in environments where you want to use MPLS QoS values that are not based on IP DSCP/IP. in this case QoS actions performed by the penultimate router can be based on MPLS EXP bits.
mpls ldp discovery targeted-hello -
this command used for Mpls Ldp Session Protection
For the protection to work, you need to enable it on both the LSRs. If this is not possible, you can enable it on one LSR, and the other LSR can accept the targeted LDP Hellos by configuring the command mpls ldp discovery targeted-hello accept.
