IPv6 SLAAC

From a pearson's question in the Odom book:

With SLAAC ,the host learns the prefix from a router using NDP RS/RA messages.
The host can use EUI-64 Rules or use a defined process to randomly generate
the interface ID value.

what is the randomly generated method is my question ?

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Comments

rob42

As with any computer generated 'Random' number, it won't be a truly random number, rather a pseudorandom number, the process behind this number is largely irrelevant. The 'number' also changes over time (as a security measure).

satishtech

I think my question would be when does a host use the eui-64 method
and when the random method ?what are the configuration steps ?

rob42

satishtech wrote: »

I think my question would be when does a host use the eui-64 method
and when the random method ?what are the configuration steps ?

Sorry, I misunderstood your question.

I'm sure that if this is inaccurate, someone here will correct me (I'm by no means an expert).

The way I understand it is...

If no DHCP server is available (could be due to admin costs or that the server is offline for some reason), a host can use SLAAC as an alternative method for assignment of its IPv6 Address, getting the first part from a Router (NDP RA) and then randomly generating the Interface ID part of its IPv6 Address, itself.

Needing only a connection to a Router, rather than to a DHCP Server avoids any service outage due to a single point of failure, i.e the DHCP Server or connection/s to it.

I can see this becoming the norm (that is to simply do way with a DHCP server) as and when companies move to IPv6, as there's far less administration with SLAAC.

Welly_59

You still need a dhcp server with ipv6 even when using slaac. Server will be needed to provide dns server addresses and default gateways

clarson

In the narrow sense of a dhcp server hands out a ipv6 address, that could come to an end.
But, in the bigger picture of things, the dhcp server isn't going anywhere.

Such as providing a lease time. In an environment with frequent user turnover, you may not want to allow a piece of equipment to use an ipv6 address until it has been removed from the network. or for servers where it should have the same ipv6 address always. or for phones that get a lot more configuration information from the dhcp server than just it's ipv6 address.

satishtech

In summary an Interface can get an IPv6 address by the following methods:

1. Manual assignment.
2. SLAAC EUI-64 method (stateless)
3. DHCP Server (Statefull )