MPLS ping and
traceroute operations for prefix SID are supported for various IGP scenarios,
for example:
-
Within an IS-IS
level or OSPF area
-
Across IS-IS
levels or OSPF areas
-
Route
redistribution from IS-IS to OSPF and from OSPF to IS-IS
The MPLS LSP Ping
feature is used to check the connectivity between ingress Label Switch Routers
(LSRs) and egress LSRs along an LSP. MPLS LSP ping uses MPLS echo request and
reply messages, similar to Internet Control Message Protocol (ICMP) echo
request and reply messages, to validate an LSP. The destination IP address of
the MPLS echo request packet is different from the address used to select the
label stack.
The MPLS LSP
Traceroute feature is used to isolate the failure point of an LSP. It is used
for hop-by-hop fault localization and path tracing. The MPLS LSP Traceroute
feature relies on the expiration of the Time to Live (TTL) value of the packet
that carries the echo request. When the MPLS echo request message hits a
transit node, it checks the TTL value and if it is expired, the packet is
passed to the control plane, else the message is forwarded. If the echo message
is passed to the control plane, a reply message is generated based on the
contents of the request message.
The MPLS LSP Tree
Trace (traceroute multipath) operation is also supported for IGP Prefix SID.
MPLS LSP Tree Trace provides the means to discover all possible equal-cost
multipath (ECMP) routing paths of an LSP to reach a destination Prefix SID. It
uses multipath data encoded in echo request packets to query for the
load-balancing information that may allow the originator to exercise each ECMP.
When the packet TTL expires at the responding node, the node returns the list
of downstream paths, as well as the multipath information that can lead the
operator to exercise each path in the MPLS echo reply. This operation is
performed repeatedly for each hop of each path with increasing TTL values until
all ECMP are discovered and validated.
MPLS echo request
packets carry Target FEC Stack sub-TLVs. The Target FEC sub-TLVs are used by
the responder for FEC validation. The IGPIPv4 prefix sub-TLV has been added to
the Target FEC Stack sub-TLV. The IGP IPv4 prefix sub-TLV contains the prefix
SID, the prefix length, and the protocol (IS-IS or OSPF).
The network node which advertised the Node Segment ID is responsible
for generating a FEC Stack Change sub-TLV with pop operation type for Node
Segment ID, regardless of whether penultimate hop popping (PHP) is enabled or
not.
The format is as below for IPv4 IGP-Prefix Segment ID:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Prefix Length | Protocol | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format is as below for IPv6 IGP-Prefix Segment ID:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 Prefix |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Prefix Length | Protocol | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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