You can use MPLS trace to determine which paths are present on an MPLS LSR.
When the TTL expires on an MPLS LSR, the echo reply that is returned includes a
downstream mapping TLV. This TLV contains all the downstream mappings of the
LSR on which the TTL expired, if that feature is supported by the LSR. You can use
the detail version of the trace mpls commands to display these downstream
mappings.
Supported TLVs
Table 24 on page 234 lists the TLVs supported by the MPLS LSP ping feature. Table
25 on page 235 lists the sub-TLVs supported for the Target FEC Stack TLV.
Table 24: TLVs Supported by MPLS LSP ping
CommentsValueType Number
Multiple FEC stack sub-TLVs are not supported. A
single LSP ping message cannot have more than
one target FEC stack TLV.
Target FEC Stack1
Only the IPv4 (numbered or unnumbered)
downstream address type is supported.
Flag I for the Interface and Label Stack object is
supported. Flag N, to treat the packet as a non-IP
packet, is not supported.
An MPLS LSP trace echo request includes this TLV.
This TLV contains the downstream address
all-routers-multicast; that is the well-known IP
address 224.0.0.2. Validation of the downstream
address is not performed.
Verification of the downstream address is not
performed on receipt of an MPLS echo request
that contains this TLV.
In an MPLS echo reply, multipath information is
not supported in this TLV; the multipath type is
always set to 0 in the reply. However, the reply
includes one downstream mapping TLV for each
downstream path.
Downstream Mapping2
This TLV is included in the MPLS echo request
packet. The TLV can specify either “ Do not reply”
or “ Reply via an IPv4/IPv6 UDP packet.”
Pad3
This TLV is generated if requested by the received
downstream mapping TLV.
Interface and Label Stack7
This TLV is generated if an error is encountered
while parsing one of the received TLVs.
Errored TLVs9
–Reply TOS Byte10
234 ■ ECMP Labels for MPLS
JUNOSe 11.1.x BGP and MPLS Configuration Guide
To Next Page
Loading...
Need help?
General
