IPv6 General Prefix and SLAAC Examples

General Prefix

This is great for allowing auto configuration on a site.  You can configure a /48 global prefix, then allocate prefixs(subnets) per derived from it!  The names global prefix can contain more than one /48 address to aid migration of a whole site.

Example:

R1(config)#ipv6 general-prefix NOTEPAD 2001:CAFE:CAFE::/48
R1(config)#int fa 0/0
R1(config-if)#ipv6 address NOTEPAD ::CAFE:0:0:0:1/64
R1(config-if)#no ipv6 nd suppress-ra

R1#show interfaces fa 0/0 FastEthernet0/0 is up, line protocol is up Hardware is i82543 (Livengood), address is ca01.5600.0008 (bia ca01.5600.0008) MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec, reliability 255/255, txload 1/255, rxload 1/255 <omitted for brevity> R1#show ipv6 int brief FastEthernet0/0 [up/up] FE80::C801:56FF:FE00:8 2001:CAFE:CAFE:CAFE::1 R1#show ipv6 interface fastEthernet 0/0 FastEthernet0/0 is up, line protocol is up IPv6 is enabled, link-local address is FE80::C801:56FF:FE00:8 No Virtual link-local address(es): General-prefix in use for addressing Global unicast address(es): 2001:CAFE:CAFE:CAFE::1, subnet is 2001:CAFE:CAFE:CAFE::/64 Joined group address(es): FF02::1 FF02::2  FF02::1:FF00:1  FF02::1:FF00:8 MTU is 1500 bytes ICMP error messages limited to one every 100 milliseconds ICMP redirects are enabled ICMP unreachables are sent ND DAD is enabled, number of DAD attempts: 1 ND reachable time is 30000 milliseconds (using 30000) ND advertised reachable time is 0 (unspecified) ND advertised retransmit interval is 0 (unspecified) ND router advertisements are sent every 200 seconds ND router advertisements live for 1800 seconds ND advertised default router preference is Medium Hosts use stateless autoconfig for addresses. R1#

Note the two solicited node multicast addresses.   The one ending :1 is from the GUA, the other is from the Link Local Address which itself is EUI-64 and derived from the interface MAC address!

Lets add a second prefix only…

R1(config)#ipv6 general-prefix NOTEPAD 2001:9999:9999::/48
R1(config)#do show ipv inter brief
FastEthernet0/0 [up/up]
   FE80::C801:56FF:FE00:8
   2001:9999:9999:CAFE::1
   2001:CAFE:CAFE:CAFE::1

SLAAC

Now let’s get addresses on the other end of the Fa0/0 link to R2 via SLAAC:

R2(config)#default interface fa 0/0
Interface FastEthernet0/0 set to default configuration

R2#show ipv6 interface fa 0/0 

(Nothing!)
R2#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#int fa 0/0

R2(config-if)#ipv6 address autoconfig 

R2(config-if)#end


R2#show ipv6 interface fa 0/0
FastEthernet0/0 is up, line protocol is up
IPv6 is enabled, link-local address is FE80::C802:4FF:FEA0:8
No Virtual link-local address(es):
Stateless address autoconfig enabled
Global unicast address(es):
2001:9999:9999:CAFE:C802:4FF:FEA0:8, subnet is 2001:9999:9999:CAFE::/64 [EUI/CAL/PRE]
valid lifetime 2591999 preferred lifetime 604799
2001:CAFE:CAFE:CAFE:C802:4FF:FEA0:8, subnet is 2001:CAFE:CAFE:CAFE::/64 [EUI/CAL/PRE]
valid lifetime 2591999 preferred lifetime 604799
Joined group address(es):
FF02::1
FF02::2
FF02::1:FFA0:8
MTU is 1500 bytes
ICMP error messages limited to one every 100 milliseconds
ICMP redirects are enabled
ICMP unreachables are sent
ND DAD is enabled, number of DAD attempts: 1
ND reachable time is 30000 milliseconds (using 30000)
ND advertised reachable time is 0 (unspecified)
ND advertised retransmit interval is 0 (unspecified)
ND router advertisements are sent every 200 seconds
ND router advertisements live for 1800 seconds
ND advertised default router preference is Medium
Hosts use stateless autoconfig for addresses.
R2#

 

Finally to show migration, I’m going to remove the first CAFE global prefix.

R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#no ipv6 general-prefix NOTEPAD 2001:CAFE:CAFE::/48

R1#show ipv6 int brief
FastEthernet0/0 [up/up]
   FE80::C801:56FF:FE00:8
   2001:9999:9999:CAFE::1

By amending the valid lifetime, you can migrate to a new prefix.

 

One thought on “IPv6 General Prefix and SLAAC Examples

  1. Pingback: IPv6 Routing – Static and Basics | Engineering Notepad

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