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Directly connected IPv6 neighbors cannot ping each other.

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TitleDirectly connected IPv6 neighbors cannot ping each other.
Reported that two directly connected ipv6 neighbors cannot communicate.
R1 = IPv4 add = ; IPv6 add = 2001:0503:f261:15ff:0000:0000:0000:0001/126
R2 = IPv4 add = ; IPv6 add = 2001:0503:f261:15ff:0000:0000:0000:0002/126
R1 can ping to R2 via ipv4 but cant ping via IPv6.
R1 can reach to all its neighbor with ipv4 and ipv6, but R2 can only reach the directly connected neighbors via IPv4 and not IPv6.
Both have identical configuration.
Both (R1 and R2) see each other in IPv6 neighbor list, but ping ipv6 is failing between them.
ICMPv6 request from R1 to R2 on debug packet capture reaching lp cpu of R2. The packet is hitting right CAM, and we see message that the packet is forwarded to MP cpu.
However, the packet is not reaching to MP cpu. In the output of show ipv6 traffic, and debug ipv6 icmp we are not seeing the ICMPv6 request on MP cpu.
When we initiate ping ipv6 from R2, ICMPv6 echo request does reach to R1 and it sends the reply back, but the reply is not reaching to MP cpu of R2.
Software Release: N/A
Fixed in Version: N/A
The user had configured ipv6 access-class VTYACL-v6 in command, but there was no associated ACL present. Therefore, the ipv6 traffic to the management was failing.

After removing the command from the configuration, the problem was fixed.
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