One of the comments to my “IPv6 in Data Center: after a year, Cisco is still not ready” post included the following facts:
Up through at least 15.0(1)M and 12.2(53)SE2 the IPv6 support for management protocols is spotty; syslog is there, SNMP traps and the RADIUS/TACACS control plane aren't.
Another bug along the same lines was discovered by Jónatan Jónasson: When the Cisco IOS Login Enhancements feature logs successful or failed login attempt, it reports the top 32 bits of the remote IPv6 address in IPv4 address format. Here’s a sample printout taken from a router running IOS release 15.0(1)M.
P# %SEC_LOGIN-5-LOGIN_SUCCESS: Login Success [user: test]
[Source: 254.192.0.0] [localport: 23] at ... P#who Line User Host(s) Idle Location * 0 con 0 idle 00:00:00 2 vty 0 test idle 00:00:06 FEC0::CCCC:1
It looks like the recommendation we’ve been making two years ago is still valid: use IPv4 for network management.