I ran across a curious occurence as I was 'playing' with ipv6 on my lab. Specifically, I noticed that, when using the 'ipv6 general-prefix' feature, deleted prefixes do not seem to disappear from 'other routers'.
Example:
On R1 I configured several general prefixes:
R1#sho run | in general
ipv6 general-prefix LAB 2001:1:2::/48
ipv6 general-prefix LAB 2001:3:4::/48
ipv6 general-prefix LAB 2001:5:6::/48
I configured an interface on R1 to formulate addresses based on these prefixes:
R1#sho run int g1.146
Building configuration...
Current configuration : 189 bytes
!
interface GigabitEthernet1.146
description link to VLAN 146 via VSwitch 2
encapsulation dot1Q 146
ip address 155.1.146.1 255.255.255.0
ipv6 address LAB ::/64 eui-64
ipv6 enable
end
Which worked as intended:
R1#sho ipv6 int bri g1.146
GigabitEthernet1.146 [up/up]
FE80::20C:29FF:FE8E:FBA2
2001:1:2:0:20C:29FF:FE8E:FBA2
2001:3:4:0:20C:29FF:FE8E:FBA2
2001:5:6:0:20C:29FF:FE8E:FBA2
It also had the (expected) effect of being used on an adjacent router (R4) whose connected interface was configured for autoconfig:
R4#sho run int g1.146
Building configuration...
Current configuration : 191 bytes
!
interface GigabitEthernet1.146
description link to VLAN 146 via VSwitch 2
encapsulation dot1Q 146
ip address 155.1.146.4 255.255.255.0
ipv6 address autoconfig default
ipv6 enable
end
R4#sho ipv6 int bri g1.146
GigabitEthernet1.146 [up/up]
FE80::20C:29FF:FE9B:470
2001:1:2:0:20C:29FF:FE9B:470
2001:3:4:0:20C:29FF:FE9B:470
2001:5:6:0:20C:29FF:FE9B:470
2001:6:6:6:20C:29FF:FE9B:470
So far, so good...
The 'odd' thing is, as I removed a couple of the general-prefixes from R1 - which automatically and immediately removed those addresses from Gig1.146 on R1:
R1(config)#no ipv6 general-prefix LAB 2001:3:4::/48
R1(config)#no ipv6 general-prefix LAB 2001:5:6::/48
R1(config)#do sho ipv6 int bri g1.146
GigabitEthernet1.146 [up/up]
FE80::20C:29FF:FE8E:FBA2
2001:1:2:0:20C:29FF:FE8E:FBA2
The deleted general-prefixes remained on R4's interface:
R4#sho ipv6 int bri g1.146
GigabitEthernet1.146 [up/up]
FE80::20C:29FF:FE9B:470
2001:1:2:0:20C:29FF:FE9B:470
2001:3:4:0:20C:29FF:FE9B:470
2001:5:6:0:20C:29FF:FE9B:470
2001:6:6:6:20C:29FF:FE9B:470
Basically, to get them to go away, I had to shut\no shut the interface - thereby disrupting service:
R4(config)#int g1.146
R4(config-subif)#shut
R4(config-subif)#no shut
R4(config-subif)#^Z
R4#
*Mar 15 2019 13:13:44.582 EDT: %SYS-5-CONFIG_I: Configured from console by console
R4#sho ipv6 int bri g1.146
GigabitEthernet1.146 [up/up]
FE80::20C:29FF:FE9B:470
2001:1:2:0:20C:29FF:FE9B:470
2001:6:6:6:20C:29FF:FE9B:470
Questions:
Is this normal\expected behavior - or is it a bug?
If it is normal, is there a non-disruptive way to clear the addresses?
If it is normal, what is the purpose?
Thanks!
