traceroute and “port unreachable”

I was trying to connect two systems using IP V6, and was despairing when I kept getting flows with errors like

This one seemed OK (from laptop to z/OS)

Internet Protocol Version 6, Src: 2001:db8:3::3, Dst: 2001:db8:8::9
    Hop Limit: 1
    Source Address: 2001:db8:3::3
    Destination Address: 2001:db8:8::9
User Datagram Protocol, Src Port: 45239, Dst Port: 33435
    Source Port: 45239
    Destination Port: 33435
        [Expert Info (Chat/Sequence): Possible traceroute: hop #1, attempt #1]

This one looked like a problem (from z/OS to laptop)

Internet Control Message Protocol v6
    Type: Destination Unreachable (1)
    Code: 4 (Port unreachable)
    Internet Protocol Version 6, Src: 2001:db8:3::3, Dst: 2001:db8:8::9
        Next Header: UDP (17)
        Hop Limit: 1
        Source Address: 2001:db8:3::3
        Destination Address: 2001:db8:8::9
    User Datagram Protocol, Src Port: 45239, Dst Port: 33435
        Source Port: 45239
        Destination Port: 33435
            [Expert Info (Chat/Sequence): Possible traceroute: hop #1, attempt #1]
      

Is this a problem?

No – this is how traceroute works

Ive explained about traceroute.

From laptop to z/OS

• Internet Protocol Version 6, Src: 2001:db8:3::3, Dst: 2001:db8:8::9
  • Hop Limit: 1 The hop count is decremented on each top
  • Source Address: 2001:db8:3::3
  • Destination Address: 2001:db8:8::9
• User Datagram Protocol, Src Port: 45239, Dst Port: 33435
  • Source Port: 45239
  • Destination Port: 33435
  • [Expert Info (Chat/Sequence): Possible traceroute: hop #1, attempt #1] This is Wireshark’s interpretation of the request.

From z/OS to laptop

• Internet Control Message Protocol v6
  • Type: Destination Unreachable (1)
  • Code: 4 (Port unreachable)
  • Internet Protocol Version 6, Src: 2001:db8:3::3, Dst: 2001:db8:8::9
  • Hop Limit: 1
  • Source Address: 2001:db8:3::3
  • Destination Address: 2001:db8:8::9
• User Datagram Protocol, Src Port: 45239, Dst Port: 33435
  • Source Port: 45239 This matches the original request
  • Destination Port: 33435 This matches the original request
  • [Expert Info (Chat/Sequence): Possible traceroute: hop #1, attempt #1] This is Wireshark’s interpretation of the data
    

In this case the “problem flows” are expected as a result of the way the traceroute command works.