Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 963)

Multi-Service IronWare Switching Configuration Guide 933
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BFD for RSVP-TE LSP
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• The IP TTL for transmitted MPLS BFD control packets from ingress LSR to egress LSR must be
set to 1 instead of 255.
• After MPLS BFD session is up, the local discriminator and the source IP address are not
allowed to change without bringing down the MPLS BFD session.
• The transmit and receive portion of the session can be on different LPs because the LSP is
unidirectional and the returned path from egress to ingress LSR depends on IP routing.
MPLS BFD is set up between the ingress and egress LSR. The MPLS BFD session uses an
asynchronous operating mode without echo function. BFD demands an operating mode and echo
function that are not currently defined for MPLS BFD. Authentication is not supported (it is currently
not supported for OSPF or ISIS either).
BFD configuration on the MLX/XMR products are provided at the global MPLS configuration level
and at the LSP level as follows:
• The global configuration provides you a convenient way to enable and disable BFD for all LSPs
that have BFD enabled (this is similar to how it is provided for ISIS and OSPF). In addition, the
you can change the default settings for transmit and receive intervals and detection time
multiplier to be used for all BFD sessions. On egress LSR, this global setting is used to decide
whether a BFD session starts upon receiving MPLS echo request with BFD Discriminator TLV
and the time intervals to be included in the BFD control packet are to be sent back to the
ingress LSR.
• Under the LSP configuration, you are able to enable or disable BFD and change the default
settings for minimum transmit and receive intervals as well as detection time multiple. If those
parameters are not specified, the values from the global configuration are used.
BFD can be enabled or disabled without program exit at the global MPLS level or for each individual
LSP without affecting the LSP operational status. In addition, the BFD parameters can also be
changed without program exit This does not change the state of the BFD session.
One BFD session is created for each non-redundant LSP. BFD session is associated with the active
path which can be normal or protected, or detour path. For redundant LSP, a separate BFD session
is created for the currently active secondary path.
In the case of a software upgrade from older Releases to 3.9 and later, BFD configuration are set to
disable at both the global level and at the LSP level.
BFD session creation
On ingress, one BFD session is created for each LSP. A BFD session is created after the LSP comes
UP. The BFD session status is displayed as part of the show LSP output. When the BFD session is
not UP, a failure reason is displayed as part of the show LSP detail output. Possible failure reasons
include exceeding the maximum number of BFD sessions the system can support or the global BFD
configuration is disabled. In the case where BFD session is not brought up because BFD packet
from the egress LSR is not received, the MPLS Echo Request with the BFD Discriminator TLV is
resent until the session is UP. The retry timer is exponentially backed off.
On egress, a BFD session is created after an MPLS Echo Request is received with the BFD
Discriminator TLV and the MPLS BFD enabled globally and the maximum number of BFD sessions
has not been reached yet. The BFD session created on egress LSR also is counted towards the
maximum number of BFD sessions. When the number of BFD sessions has reached a maximum,
neither the MPLS Echo Reply nor the BFD control packet are sent. The ingress LSR will retry.