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Cisco Bug: CSCvu15362 - SR-MPLS multipath traceroute does not work correctly due to router-alert bit set in packet

Last Modified

Aug 25, 2020

Products (5)

  • Cisco 8000 Series Routers
  • Cisco 8201 Router
  • Cisco 8808 Router
  • Cisco IOS XR Software
  • Cisco 8812 Router

Known Affected Releases

7.0.12

Description (partial)

Symptom:
SR-MPLS traceroute with multi-path option fails in the SR-MPLS network when it has a 8000 series router that is responding to the MPLS echo request.

Sample output from a verifying Router which is sending the MPLS echo request.
Note that these IP addresses are samples to describe the problem and derived in the Engineering lab.
They are no way intended to depict a typical customer network.

RP/0/RP0/CPU0:r4#traceroute sr-mpls multipath 119.0.0.6/32 source 119.0.0.4 fec-type igp isis verbose
Fri Apr 17 13:32:30.314 PDT

Starting LSP Path Discovery for 119.0.0.6/32

Codes: '!' - success, 'Q' - request not sent, '.' - timeout,
'L' - labeled output interface, 'B' - unlabeled output interface,
'D' - DS Map mismatch, 'F' - no FEC mapping, 'f' - FEC mismatch,
'M' - malformed request, 'm' - unsupported tlvs, 'N' - no rx label,
'P' - no rx intf label prot, 'p' - premature termination of LSP,
'R' - transit router, 'I' - unknown upstream index,
'X' - unknown return code, 'x' - return code 0

Type escape sequence to abort.

LD!
Path 0 Broken,
output interface Bundle-Ether3 nexthop 119.1.48.8
source 119.0.0.4 destination 127.0.0.1
0 119.0.0.4 119.1.48.8 MRU 1500 [Labels: 463946 Exp: 0] multipaths 0
L 1 119.1.48.8 119.1.58.5 MRU 1500 [Labels: 463946 Exp: 0] ret code 8 multipaths 3
D 2 119.9.28.2 119.1.26.6 MRU 1500 [Labels: implicit-null Exp: 0] ret code 5 multipaths 1
! 3 119.1.26.6, ret code 3 multipaths 0
D!
Path 1 Broken,
output interface Bundle-Ether3 nexthop 119.1.48.8
source 119.0.0.4 destination 127.0.0.0
0 119.0.0.4 119.1.48.8 MRU 1500 [Labels: 463946 Exp: 0] multipaths 0
L 1 119.1.48.8 119.9.28.2 MRU 1500 [Labels: 463946 Exp: 0] ret code 8 multipaths 3
D 2 119.1.58.5 119.1.56.6 MRU 1500 [Labels: implicit-null Exp: 0] ret code 5 multipaths 1
! 3 119.1.56.6, ret code 3 multipaths 0
L!
Path 2 found,
output interface Bundle-Ether3 nexthop 119.1.48.8
source 119.0.0.4 destination 127.0.0.4
0 119.0.0.4 119.1.48.8 MRU 1500 [Labels: 463946 Exp: 0] multipaths 0
L 1 119.1.48.8 110.28.1.2 MRU 1500 [Labels: 463946 Exp: 0] ret code 8 multipaths 3
L 2 110.28.1.2 119.1.26.6 MRU 1500 [Labels: implicit-null Exp: 0] ret code 8 multipaths 1
! 3 119.1.26.6, ret code 3 multipaths 0

Paths (found/broken/unexplored) (1/2/0)
Echo Request (sent/fail) (7/0)
Echo Reply (received/timeout) (7/0)
Total Time Elapsed 30 ms

Conditions:
The 8000 series router is running Cisco IOS-XR 7.0.12 release
The 8000 series router is having ECMP paths towards the MPLS echo destination
The 8000 series router is the intermediate Router that reports the multiple ECMP paths (reachability to the MPLS echo destination)  to the originator of the MPLS echo request.
The Router under scrutiny can be the first hop or intermediate hop or the penultimate hop for the Destination.
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Bug Details Include

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