Stateless autoconfiguration for IPv6

good article. But I could not get ipv6 address from my neighbor router in gns3 ((

Did you enable the interfaces? It worked fine on a couple of 3600 routers in GNS3.

it works for me. using 7200

Hi Rene,

How the IPV6 assign the default route?

Davis

Hi Davis,

It is similar to how IPv4 default routes work. Instead of 0.0.0.0/0 we use ::/0 for IPv6. You can advertise this with routing protocols or use a static route.

The default gateway works a bit differently.

A host will receive router advertisement(s) from all routers on the subnet. The router with the highest RA preference will be used as the default gateway.

Rene

Hi Rene,

Do you have lesson configure the RA preferences? More on how the LAN host get the DHCPV6 address and which router will be the elect as default gateway.

And the show ipv6 router command is something like show arp in IPV4?

Davis

 

Hi Davis,

Take a look here:

The show ipv6 router command will show you all local routers where you received a router advertisement from. The IPv6 equivalent of show arp is show ipv6 neighbors.

Rene

Dear Rene,

Awesome explanation! I miss out this lesson. Thanks!

Davis

Hi Davis

I know it’s a bit of a late response but just to add onto this. On the client you can also add the syntax “default” after the statement “ipv6 address autoconfig”

e.g. “ipv6 address autoconfig default”. This will inject a default route on your client.

please check:-
The big difference between DHCP for IPv6 and DHCPv6 is that we don’t use broadcast traffic anymore”

I think you mean DHCP for IPv4

Hi Nassir,

That’s correct, thanks for letting me know. Just fixed it.

Rene

Hello rené
Do we have to use ipv6 as the “marked in marble” ipv4 addresses or are IPV6 autoconfig addresses “leased addresses” ?

for example, if a new equipement (new ports, with new mac; or maintenance) is added to a router, does he find the same mandatory ip when he restarts ?
then (if the maintenance change all the router) is it a best practice to write in the new router a static address with the same eui/64 form than the old router ? or is it préférable to have new on in this case ?

Hello Hugues

When using SLAAC, the addresses that are configured depend on the operating system being used. Specifically for Cisco IOS devices, the EUI64 process is used by default. This means that the actual IPv6 address that a Cisco device will obtain will depend directly on the MAC address of the device itself. If this device is then removed and another device is put in its place, because MAC addresses are unique, the new IPv6 address it will obtain will be different. If the same device is shutdown and restarted, then the same IPv6 address will be assigned to the device once again.

Well, it really depends on what you want. Typically, for network equipment, it is preferable to use a static address so that remote administration can take place over the same destination IP address.

I hope this has been helpful!

Laz

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Hello, thanks for the lesson. In this video you show for example how to configure Stateless autoconfiguration. But is this the same as SLAAC(stateless Address Autoconfiguration)?

Best regards Lars

Hello Lars

Yes, Stateless Autoconfiguration for IPv6 is the same thing as SLAAC.

Laz

Hi Guys - two quick questions…

Is ipv6 address autoconfig all we need to configure SLAAC?

Is SLAAC used exclusively for link local addresses?

Thanks,

Gareth.

Hello Gareth

From the client side, yes that command is all that you need. You must also have an IPv6 enabled router connected to the subnet of that interface in order for the autoconfig to function.

SLAAC is used only for global unicast addresses. Link local addresses are generated either using the EUI-64 method, or randomly. (Cisco uses EUI-64 by default, Microsoft Windows, for example, uses a random algorithm for their hosts). Link local IPv6 address generation does not require the presence of an IPv6 router on the subnet as it generates the address completely independently of any other device. SLAAC requires the existence of an IPv6 router on the subnet to function.

I hope this has been helpful!

Laz

Ok - that makes sense - thanks Laz.

So if you enabled SLAAC this process would automatically configure the /64 network bits of all the Global Unicast addresses on your subnet?

Does this mean you would still end up with EUI-64 addresses as the second 64 host bits of the Global Unicast address?

Would this make the admin a little bit more complicated as the host bits wouldn’t follow a set pattern as an ipv4 administered network where you could allocate sequentially numbered hosts?

Hello Gareth

Yes. The network portion of the address is determined by the SLAAC-enabled router on the subnet. In the lesson you can see that R2 sent information to R1 that told it to use the same prefix as its own:

R2# 
ICMPv6-ND: Sending RA to FF02::1 on FastEthernet0/0
ICMPv6-ND:     MTU = 1500
ICMPv6-ND:     prefix = 2001:1234::/64 onlink autoconfig

The method by which the host bits are determined depends once again on the vendor. Typically, this is determined using the EUI-64 method (so you will see that the host bits are the same as those on the link local address on a Cisco device), but some hosts use other methods such as Microsoft, for these bits. More information on the specific method for determining these bits used by Microsoft and others can be found at RFC4941.

As an administrator, how IPv6 allocates the network bits of the hosts in a subnet wouldn’t bother me very much. Because this whole process of SLAAC automates much of the administration process, I would be less concerned about how the allocation is achieved. The benefits here are: configure the local router, configure hosts to use SLAAC and that’s it. No DHCP parameters, scopes, options or anything else.

I hope this has been helpful!

Laz

Thanks Laz - your comprehensive answer is much appreciated! :):smile:

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