LSP
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... data plane failures in MPLS Label Switched Paths
(LSPs). There are two parts to this document: information carried in
an MPLS "echo request ...
... The body of this memo contains four main parts: motivation, MPLS echo
request/reply packet format, LSP ping operation, and a reliable
return path. It is suggested that first-time readers skip the actual
packet formats ...
...
When an LSP fails to deliver user traffic, the failure cannot always
be detected by the MPLS control plane ...
... traceroute"
mode for testing MPLS LSPs.
The basic idea is to verify that packets that belong to a particular
...
...
As described above, LSP ping is intended as a diagnostic tool. It is
intended to enable providers of an MPLS-based ...
... service to isolate
network faults. In particular, LSP ping needs to diagnose situations
where the control and data planes ...
... services also need the ability to trace all
of the possible paths that an LSP may take. Since most MPLS services
...
... requirements:
1. Although the LSP in question may be broken in unknown ways, the
likelihood of a diagnostic packet being delivered to a user of an
MPLS ...
... service MUST be held to an absolute minimum.
2. If an LSP is broken in such a way that it prematurely terminates,
the diagnostic packet MUST NOT be IP forwarded.
...
... range, it would still be possible for the
first recipient of a diagnostic packet that "escaped" from a broken
LSP to have that address assigned to the interface on which it
...
... ECMP paths. Finally, as
an implementation optimization, the 127/8 provides an easy means of
identifying possible LSP packets.
...
... A description of the Types and Values of the top-level TLVs for LSP
ping are given below:
Type # Value Field ...
... address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero | LSP ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
... | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Must Be Zero | LSP ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
... This FEC is deprecated and is retained only for backward
compatibility. Implementations of LSP ping SHOULD accept and process
this TLV, but SHOULD send LSP ping ...
... LSP ping SHOULD accept and process
this TLV, but SHOULD send LSP ping echo requests with the new TLV
...
... receiving this TLV SHOULD use the source IP address of the LSP
echo request to infer the sender ...
... FEC is used if the
protocol advertising the label is unknown or may change during the
course of the LSP. An example is an inter-AS LSP that may be
...
... course of the LSP. An example is an inter-AS LSP that may be
signaled by LDP in one Autonomous System ...
...
An MPLS echo request is used to test a particular LSP. The LSP to be
tested is identified by the "FEC Stack ...
... An MPLS echo request is used to test a particular LSP. The LSP to be
tested is identified by the "FEC Stack"; for example, if the LSP ...
... LSP to be
tested is identified by the "FEC Stack"; for example, if the LSP was
set up via LDP, and is to an egress IP address ...
... with value 10.1.1.1/32. If the LSP being tested is an RSVP LSP, the
FEC Stack consists of a single element ...
... IPv4 prefix of 10.1/8 that is tunneled over an LDP LSP with
egress 10.10.1.1. The FEC Stack would then contain two sub-TLVs ...
... point-to-point tunnels. Frequently, a single
LSP may originate at several ingresses, and terminate at several
egresses; this is very common with LDP LSPs ...
... LSP may originate at several ingresses, and terminate at several
egresses; this is very common with LDP LSPs. LSPs for a given FEC
...
... egresses; this is very common with LDP LSPs. LSPs for a given FEC
may also have multiple "next hops ...
... next hops" at transit LSRs. At an ingress,
there may also be several different LSPs to choose from to get to the
desired endpoint. Finally, LSPs ...
... LSPs to choose from to get to the
desired endpoint. Finally, LSPs may have backup paths, detour paths,
and other alternative paths to take should the primary LSP go down.
...
... endpoint. Finally, LSPs may have backup paths, detour paths,
and other alternative paths to take should the primary LSP go down.
To deal with the last two first: it is assumed that the LSR ...
... MPLS echo requests can force the echo request into any desired LSP,
so choosing among multiple LSPs at the ingress is not an issue. The
...
... echo request into any desired LSP,
so choosing among multiple LSPs at the ingress is not an issue. The
problem of probing the various flavors of backup paths that will
typically not be used for forwarding data unless the primary LSP ...
... LSPs at the ingress is not an issue. The
problem of probing the various flavors of backup paths that will
typically not be used for forwarding data unless the primary LSP is
down will not be addressed here.
...
... down will not be addressed here.
Since the actual LSP and path that a given packet may take may not be
known a priori, it is useful if MPLS echo ...
... MPLS traceroute
message to determine whether there are multipaths for a given LSP.
If so, each hop will provide some information how each of its
downstream ...
... an MPLS echo request packet with at least one additional label when
testing LSPs that are used to carry MPLS payloads (such as LSPs ...
... LDP or
RSVP-TE LSPs, just sending an MPLS echo request packet may not detect
instances where the router ...
... upstream of the destination of
the LSP ping may forward the MPLS echo request successfully over an
interface ...
... FEC label mapping that describes how traffic received on
the LSP is further switched or which application it is associated
with. If no mapping exists, set FEC-return-code to Return 4,
...
... port is the well-known UDP port for LSP
ping. The destination IP address and UDP port are copied from the
...
... the Router Alert IP option. If the reply is sent over an LSP, the
topmost label MUST in this case be the Router Alert label (1) (see
...
... traceroute" mode, a transit LSR does not support
LSP ping, then no reply will be forthcoming from that LSR for some
...
... Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209prop, December 2001. ...
... MPLS echo requests and replies. The third is an
unauthorized source using an LSP ping to obtain information about the
network.
...
... To avoid potential Denial-of-Service attacks, it is RECOMMENDED that
implementations regulate the LSP ping traffic going to the control
plane. A rate limiter SHOULD be applied to the well-known ...
... echo
requests or replies; however, if these messages are indeed hijacked,
LSP ping will report that the data plane is not working as it should.
...