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Cisco Bug: CSCvt29250 - [CUPS]TTL(Hoplimt) handling is different between IPv4 and IPv6.

Last Modified

Jun 17, 2020

Products (2)

  • Cisco ASR 5000 Series
  • Cisco ASR 5500

Known Affected Releases

21.16.4 21.16.c11 21.16.c9.74593 21.19.0 21.19.n1

Description (partial)

Symptom:
TTL(Hoplimt) handling is different between IPv4 and IPv6.

Conditions:
Based on pcap file from monitor subscriber "vpp_S1_B0_ip_440511907330050_03022020232512_000000000.pcap" which is taken by real UE.
We can see below behavior.

IPv6:
Uplink #62-64 : hoplimit 255->254 ( 1 reduction in SAEGW )
Uplink #65-66 : hoplimit 255 ( no reduction )
Downlink #55,60-61 : hop limit 118->116 (2 reduction in SAEGW )
Downlink #84-85 : hop limit 118->117 (1 reduction in SAEGW )

IPv4:
Uplink : there is no reduction
Downlink #200-202 : TTL 53 -> 51 ( 2 reduction in SAEGW )
Downlink #514-515 : TTL 53 ->52 ( 1 reduction in SAEGW )

# You can filter pcap by "tcp.stream eq 1"  or "tcp.stream eq 3" or "tcp.stream eq 9" for finding relevant log.

As CX internal test, seems working as below:
IPv4 Uplink slowpath	0 
IPv4 Uplink fastpath	0 
IPv4 Downlink slowpath	-2 
IPv4 Downlink fastpath	-1 
Ipv6 Uplink slowpath	-1
Ipv6 Uplink fastpath	0
Ipv6 Downlink slowpath	-2
Ipv6 Downlink fastpath	-1
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