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lendawg137
Beginner

IPv6 subnet rounter anycast address

In wendell odom's book, Chapter 30: Implementing IPv6 Addressing on Routers, page 723, "...the subnet router anycast address has same subnet number as the subnet id and all binary 0s in the interface id...", yet in his example 30-9 the anycast address is 2001:1:1:2::99/128. 

 

With the /128 prefix, I can't see the "all binary 0s" in the Interface ID, and how is there any Interface ID if the IPv6 address is the entire 128 bits

2 REPLIES 2
Harold Ritter
Cisco Employee

The subnet ID of all 0 is just the default value for the IPv6 anycast address.

 

Router(config-if)#ipv6 address 2001:db8:12ff:12::/64
%GigabitEthernet0/1: Warning: 2001:DB8:12FF:12::/64 is a Subnet Router Anycast
Router(config-if)#

 

As indicated in the book, you can choose any value you want by configuring the anycast address with the "anycast" keyword.

 

Router(config-if)#ipv6 address 2001:DB8:12FF:12::99/64 anycast
Router(config-if)#do sh ipv6 int gi0/1
GigabitEthernet0/1 is up, line protocol is up
IPv6 is enabled, link-local address is FE80::F816:3EFF:FEEA:BC52
No Virtual link-local address(es):
Global unicast address(es):
2001:DB8:12FF:12::1, subnet is 2001:DB8:12FF:12::/64
2001:DB8:12FF:12::99, subnet is 2001:DB8:12FF:12::/64 [ANY]
...

 

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
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Cuauhtémoc, Juárez
Ciudad de México, 06600
México
lendawg137
Beginner

Sorry, I'm a year late. Thanks for the reply.