Specifications

trace mpls
MP-831
Cisco IOS Multiprotocol Label Switching Command Reference
January 2010
Command History
Usage Guidelines Use the trace mpls command to validate, test, or troubleshoot IPv4 LDP LSPs and IPv4 Resource
Reservation Protocol (RSVP) TE tunnels.
UDP Destination Address Usage
The destination address is a valid 127/8 address. You can specify a single address or a range of numbers
from 0.0.0 to x.y.z, where x, y, and z are numbers from 0 to 255 and correspond to the 127.x.y.z
destination address.
The MPLS echo request destination address in the UDP packet is not used to forward the MPLS packet
to
the destination router. The label stack that is used to forward the echo request routes the MPLS packet
to the destination router. The 127/8 address guarantees that the packets are routed to the localhost (the
default loopback address of the router processing the address) if the UDP packet destination address is
used for forwarding.
In addition, the destination address is used to adjust load balancing when the destination address of the
IP pa
yload is used for load balancing.
Time-to-Live Keyword Usage
The time-to-live value indicates the maximum number of hops a packet should take to reach its
destination. The value in the TTL field in a packet is decremented by 1 each time the packet travels
through a router.
For MPLS LSP ping, the TTL is a value after which the packet is discarded and an MPLS echo reply is
sen
t back to the originating router.
For MPLS Multipath LSP Traceroute, the TTL is a maximum time-to-live value and is used to discover
t
he number of downstream hops to the destination router. MPLS LSP Traceroute incrementally increases
the TTL value in its MPLS echo requests (TTL = 1, 2, 3, 4, ...) to accomplish this.
Release Modification
12.0(27)S This command was introduced.
12.2(18)SXE The r
eply dscp and reply pad-tlv keywords were added.
12.4(6)T The following keywords were added: f
orce-explicit-null, output interface,
flags fec, and revision.
12.2(28)SB This command was integrated into Cisco IOS Release 12.2(28)SB and
i
mplemented on the Cisco 10000 series routers.
12.0(32)SY This command was integrated into Cisco IOS Release 12.0(32)SY.
12.4(11)T This command was integrated into Cisco IOS Release 12.4(11)T.
12.2(31)SB2 This command was integrated into Cisco IOS Release 12.2(31)SB2. The
ne
xthop keyword was added.
12.2(33)SRB This command was integrated into Cisco IOS Release 12.2(33)SRB.
12.2(33)SXH This command was integrated into Cisco IOS Release 12.2(33)SXH.
12.0(33)S This command was integrated into Cisco IOS Release 12.0(33)S.
12.4(20T This command was integrated into Cisco IOS Release 12.4(20)T.
12.2(33)SXI This command was integrated into Cisco IOS Release 12.2(33)SXI.
Cisco IOS XE Release
2.
3
The segment keyword was added.
12.2(33)SRE This command was modified. Restrictions were added to the pseudo
wire
keyword.