Brocade Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide (Supporting R05.6.00) - Manual (Page 398)

374 Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide
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LDP over RSVP (for transit LSR only)
2
Syntax: show mpls ldp targeted-peer
TTL propagation for LDP over RSVP packets
TTL propagation for LDP over RSVP packets is controlled by the propagate-ttl command, and the
label-propagate-ttl command:
• When the label operation involves the swap of the LDP label followed by the push of the RSVP
label, the label-propagate-ttl command controls the propagation of the LDP label TTL to the
RSVP label TTL. By default, the TTL is not propagated. The RSVP label TTL is set to 255. When
the label-propagate-ttl command is configured by the user, the LDP label TTL is propagated to
the RSVP label TTL.
• When the label operation involves the POP (or the removal) of the LDP label followed by the
push of the RSVP label, the following two cases are considered:
- When the LDP label is not the only label in the Layer 2 or Layer 3 VPN stack, the
label-propagate-ttl command controls the propagation of TTL from the outer LDP label to
the VC label and, in turn, from the VC label to the RSVP label. By default, the
label-propagate-ttl command is turned off. The VC label TTL is not affected when the LDP
tunnel label and the RSVP label TTL are set to 255.
- When the LDP label is the only label in the IP over MPLS stack, the propagate-ttl command
controls the propagation of TTL from the LDP label to the IP header and, in turn, from the
IP header to the RSVP label. By default, the propagate-ttl command is turned on.
By default, TTL propagation is enabled for IP over MPLS traffic when an RSVP and an LDP tunnel
terminate on the same node. For traceroute purposes, when an RSVP tunnel is traced, then TTL
propagation must be enabled.
NOTE
There is no label-propagate-ttl command on the NetIron CES and NetIron CER devices. The
propagation of LDP label TTL to RSVP label TTL is controlled by the propagate-ttl command. By
default, propagate-ttl is enabled, therefore TTL is propagated.
Case 1: SWAP LDP and PUSH RSVP - LDP label TTL is propagated to RSVP label TTL.
Case 2: POP LDP and PUSH RSVP - Outer LDP label TTL is propagated to VC label and IP header and
then from VC label and IP header to RSVP label. When the no propagate-ttl command is configured,
then TTL is not propagated in the above scenarios, LDP and RSVP label has a TTL value of 255. The
LDP and RSVP label TTL is decremented for every hop traversed. Both the VC label and IP header
TTL is not affected by LDP and RSVP label TTL. However, at PHP, when no propagate-ttl is configured,
after the outermost Label is popped, and when there is no MPLS header but an IP header, then the
IP header TTL is decremented by 1.
NOTE
For consistent behavior in all cases of TTL propagation for LDP over RSVP packets, Brocade
recommends that the user always turn on or turn off both the label-propagate-ttl command and the
propagate-ttl command.