Cisco Bug: CSCvs02859 - NCS5500 forwards mpls label over unlabelled tunnel-te when loadbalancing with labelled tunnel
Jun 23, 2020
- Cisco ASR 9000 Series Aggregation Services Routers
- Cisco Network Convergence System 5508
- Cisco IOS XR Software
Known Affected Releases
Release-note Symptom: An NCS5500 incorrectly forwards MPLS frames over a tunnel-te interface while this tunnel-te interface is supposed to be "unlabelled" as it's not configured under LDP Drops due to unknown mpls label at the tail-end router of a tunnel-te. For instannce, on an NCS5500, these would be detected by having the "RxTrapMplsUnknownLabel" counter increment in "show contr npu stats traps-all". But there would be different counters on different platforms to indicate that mpls frames with unknown mpls label are getting dropped. MID node TE with mix label and unlabelled path not working. Conditions: An NCS5000 is the MPLS TE headend of 2 TE tunnels and some IGP prefixes are loadbalanced between these 2 tunnel-te interfaces: - One of these 2 tunnel-te must have LDP enabled (the tunnel-te interface is configured under "mpls ldp") - The other tunnel-te interface must not be configured under LDP. The mpls forwarding entry for that IGP prefix would look like: P/0/RP0/CPU0:router#sh mpls forwarding labels 32024 Wed Oct 23 17:15:56.258 CEST Local Outgoing Prefix Outgoing Next Hop Bytes Label Label or ID Interface Switched ------ ----------- ------------------ ------------ --------------- ------------ 32024 32011 192.168.2.0/24 tt13 192.168.1.11 0 Unlabelled 192.168.2.0/24 tt28 192.168.1.12 0 RP/0/RP0/CPU0:router# We can see that there are 2 paths, both paths over a tunnel-te interface, one with an outgoing label and one "unlabelled" path. The same problem would problem occur if there's more than 2 paths but with some labelled and unlabelled paths. TE mid node with ecmp path with mix label and unlabelled.
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