Cisco ASR 900 Series User Manual

time-to-live
]
Here is an example of how a loop operates if you use the following keywords and arguments on the trace
mpls command:
Device# trace mpls
ipv4
10.131.159.251/32 destination 127.0.0.1 127.0.0.1 1 ttl 5
Tracing MPLS Label Switched Path to 10.131.159.251/32, timeout is 2 seconds
Codes: '!' - success, 'Q' - request not transmitted,
'.' - timeout, 'U' - unreachable,
'R' - downstream router but not target
Type escape sequence to abort.
Destination address 127.0.0.1
0 10.131.191.230 MRU 1500 [Labels: 19 Exp: 0]
R 1 10.131.159.226 MRU 1504 [implicit-null] 40 ms
! 2 10.131.159.225 40 ms
Destination address 127.0.0.2
0 10.131.191.230 MRU 1500 [Labels: 19 Exp: 0]
R 1 10.131.159.226 MRU 1504 [implicit-null] 40 ms
! 2 10.131.159.225 40 ms
Destination address 127.0.0.3
0 10.131.191.230 MRU 1500 [Labels: 19 Exp: 0]
R 1 10.131.159.226 MRU 1504 [implicit-null] 40 ms
! 2 10.131.159.225 48 ms
An mpls trace command is sent for each TTL from 1 to the maximum TTL (ttl maximum-time-to-live keyword
and argument) for each destination address until the address specified with the destination end-address
argument is reached. For this example, the maximum TTL is 5 and the end destination address is 127.0.0.1.
The MPLS LSP Traceroute loop sequence is as follows:
destination address 1 (address-start
)
for (ttl
from 1 to maximum-time-to-live
)
send an lsp trace
destination address 2 (address-start
+ address-increment
)
for (ttl
from 1 to maximum-time-to-live
)
send an lsp trace
destination address 3 (address-start
+ address-increment
+ address-increment
)
for (ttl
from 1 to
maximum-time-to-live)
send an lsp trace
.
.
.
until destination address = address-end
MPLS Echo Request Packets Not Forwarded by IP
Multiprotocol Label Switching (MPLS) echo request packets sent during a label switched path (LSP) ping
are never forwarded by IP. The IP header destination address field in an MPLS echo request packet is a
127.x.y.z /8 address. Devices should not forward packets using a 127.x.y.z /8 address. The 127.x.y.z /8 address
corresponds to an address for the local host.
MPLS Basic Configuration Guide, Cisco IOS XE Everest 16.5.1 (Cisco ASR 900 Series)
81
MPLS LSP Ping, Traceroute, and AToM VCCV
MPLS Echo Request Packets Not Forwarded by IP

Cisco ASR 900 Series Specifications

General

Brand	Cisco
Model	ASR 900 Series
Category	Network Router
Language	English