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MPLS and RSVP-TE
where:
This calculation is performed by the IGP and passed to the SR module each time it
changes due to an updated resolution of the node SID.
The 7705 SAR also provides the MTU for the adjacency SID tunnel because it is
needed in an SR-TE LSP if the first hop in the ERO is an adjacency SID. In that case,
the calculation for SR_Tunnel_MTU, initially introduced for a node SID tunnel, is
applied to get the MTU of the adjacency SID tunnel.
The MTU of the SR-TE LSP is derived as follows:
SRTE_LSP_MTU = SR_Tunnel_MTU – numLabels×4
where:
This calculation is performed by the SR module and is updated each time the SR-TE
LSP path changes or the SR tunnel it is using is updated.
118
• Cfg_SR_MTU is the MTU configured by the user for all SR tunnels within a
particular IGP instance using config>router>ospf/isis>segment-
routing>tunnel-mtu. If no value was configured by the user, the SR tunnel MTU
will be fully determined by the IGP interface calculation. This calculation is
performed by the IGP and passed to the SR module each time it changes due
to an updated resolution of the node SID.
• IGP_Tunnel_MTU is the minimum of the IS-IS or OSPF interface MTU among
all the ECMP paths or among the primary and LFA backup paths of this SR
tunnel.
• frr-overhead is set to 1 if segment-routing and remote-lfa options are enabled
in the IGP instance; otherwise, it is set to 0.
• SR_Tunnel_MTU is the MTU SR tunnel shortest path that the SR-TE LSP is
using. The 7705 SAR also provides the MTU for the adjacency SID tunnel
because it is needed in an SR-TE LSP if the first hop in the ERO is an adjacency
SID. In that case, the calculation for SR_Tunnel_MTU (given above), initially
introduced for a node SID tunnel, is applied to get the MTU of the adjacency SID
tunnel.
• numLabels is the number of labels found in the super NHLFE of the SR-TE
LSP. At LER, the super NHLFE is pointing to the SR tunnel NHLFE, which has
a primary and a backup NHLFE.
Use subject to Terms available at: www.nokia.com
© 2022 Nokia.
MPLS Guide
3HE 18686 AAAB TQZZA
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