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IPv6 ND and NUD

Hi,


I need some feedback to verify if what Im seeing for IPv6 Neighbour Discovery state changes is correct and Im interpreting the behaviour and debugs correctly


Neighbour on my router is in REACH state and traffic is flowing to/from this neighbour (using 2001:DB8 to hide real addressing)

ROUTER#sh ipv6 nei
IPv6 Address Age Link-layer Addr State Interface
FE80::1849:F298:B1E2:A0AD 0 34e6.d739.01e3 REACH Fa0
2001:DB8:F100:100:609C:5839:F693:3F28 0 34e6.d739.01e3 REACH Fa0

FastEthernet0 has link local configured to be fe80::1


this is what we see in debug ipv6 nd

001495: *Dec 7 20:52:07.432 CET: ICMPv6-ND: REACH -> STALE: FE80::1849:F298:B1E2:A0AD
001496: *Dec 7 20:52:09.728 CET: ICMPv6-ND: Received NS for FE80::1 on FastEthernet0 from FE80::1849:F298:B1E2:A0AD
001497: *Dec 7 20:52:09.728 CET: ICMPv6-ND: Sending NA for FE80::1 on FastEthernet0
001498: *Dec 7 20:52:09.732 CET: ICMPv6-ND: STALE -> DELAY: FE80::1849:F298:B1E2:A0AD
001503: *Dec 7 20:52:14.788 CET: ICMPv6-ND: DELAY -> PROBE: FE80::1849:F298:B1E2:A0AD
001504: *Dec 7 20:52:14.788 CET: ICMPv6-ND: Sending NS for FE80::1849:F298:B1E2:A0AD on FastEthernet0
001505: *Dec 7 20:52:14.792 CET: ICMPv6-ND: Received NA for FE80::1849:F298:B1E2:A0AD on FastEthernet0 from FE80::1849:F298:B1E2:A0AD
001506: *Dec 7 20:52:14.792 CET: ICMPv6-ND: PROBE -> REACH: FE80::1849:F298:B1E2:A0AD
001525: *Dec 7 20:52:44.844 CET: ICMPv6-ND: REACH -> STALE: FE80::1849:F298:B1E2:A0AD

My understanding is as follows:

  1. After 30 sec (default ipv6 nei reachabilty time) the neighbour will change from REACH to STALE reagrdless of whether there is traffic still flowing to the neighbour or not
  2. If traffic is still flowing to this neighbour when it moves to STALE, one of two things will happen

i. either it will move from STALE to DELAY wait for (x time) for any upper layer traffic to verify reachability (eg TCP), not find any, move to PROBE, send NS every 1 second, recieve NA, and move from PROBE back to REACH. This is what we see in the debug

ii. or it will move from STALE to DELAY, wait for (x time) for any upper layer traffic, find such upper layer traffic which shows reachability, and move straight back to REACH (ie no PROBE). we dont see the debug but is this a possible option ?

Is the above correct ? of course in the debug we see (i) not (ii) for moving back to REACH although both are possible based on upper layer traffic ?

Is moving from STALE direct to REACH a possible situation ?

Is NUD this process above, ie moving from REACH to STALE every 30 sec and back to REACH based on traffic flowing, or is NUD something different ?

thanks

Mark

1 ACCEPTED SOLUTION

Accepted Solutions
VIP Advisor

Hi Mark,

Hi Mark,

Take a look at this excellent document:

https://supportforums.cisco.com/document/12217861/hitchhikers-guide-troubleshooting-ipv6

...also take a look an Andrews CiscoLive presentation, which spends a little time discussing  the ND state diagram (@12:40):

https://www.ciscolive.com/online/connect/sessionDetail.ww?SESSION_ID=76583

cheers,

Seb.

1 REPLY 1
VIP Advisor

Hi Mark,

Hi Mark,

Take a look at this excellent document:

https://supportforums.cisco.com/document/12217861/hitchhikers-guide-troubleshooting-ipv6

...also take a look an Andrews CiscoLive presentation, which spends a little time discussing  the ND state diagram (@12:40):

https://www.ciscolive.com/online/connect/sessionDetail.ww?SESSION_ID=76583

cheers,

Seb.

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