IPv6 and Address Change

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Apr 13th, 2009
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Hi all,

I just started testing IPv6, and this question regard address autoconfiguration came across.

If I have static routes pointing to a gateway IPv6 address automatically assigned (IEU-64) and for some reason I have to replace this gateway, the gateway address will change so I will have to recreate all my static routes, right? So address autoconfiguration will cause problem in this case.

The same type of problem can occur with a host with a global unicast address; if I have to replace the NIC or even the complete hardware I will have to reconfigure the DNS.

Every configuration that I made using the IPv6 autoconfigured address will be lost.

Am I missing anything here?

Paulo Roque

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pkurdziel Mon, 04/13/2009 - 18:27
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With stateless autoconfig the device will listen for advertisements from the gateway.

Here is some more info:

The following is a summary of the steps a device takes when using stateless autoconfiguration:

1. Link-Local Address Generation: The device generates a link-local address. Recall that this is one of the two types of local-use IPv6 addresses. Link-local addresses have “1111 1110 10” for the first ten bits. The generated address uses those ten bits followed by 54 zeroes and then the 64 bit interface identifier. Typically this will be derived from the data link layer (MAC) address as explained in the topic on interface identifiers, or it may be a “token” generated in some other manner.

2. Link-Local Address Uniqueness Test: The node tests to ensure that the address it generated isn't for some reason already in use on the local network. (This is very unlikely to be an issue if the link-local address came from a MAC address but more likely if it was based on a generated token.) It sends a Neighbor Solicitation message using the Neighbor Discovery (ND) protocol. It then listens for a Neighbor Advertisement in response that indicates that another device is already using its link-local address; if so, either a new address must be generated, or autoconfiguration fails and another method must be employed.

3. Link-Local Address Assignment: Assuming the uniqueness test passes, the device assigns the link-local address to its IP interface. This address can be used for communication on the local network, but not on the wider Internet (since link-local addresses are not routed).

4. Router Contact: The node next attempts to contact a local router for more information on continuing the configuration. This is done either by listening for Router Advertisement messages sent periodically by routers, or by sending a specific Router Solicitation to ask a router for information on what to do next. This process is described in the section on the IPv6 Neighbor Discovery protocol.

5. Router Direction: The router provides direction to the node on how to proceed with the autoconfiguration. It may tell the node that on this network “stateful” autoconfiguration is in use, and tell it the address of a DHCP server to use. Alternately, it will tell the host how to determine its global Internet address.

6. Global Address Configuration: Assuming that stateless autoconfiguration is in use on the network, the host will configure itself with its globally-unique Internet address. This address is generally formed from a network prefix provided to the host by the router, combined with the device's identifier as generated in the first step.

pauloroque Wed, 04/15/2009 - 12:16
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Have you read my question?

What you answered has nothing to do with the question?

greg.washburn Wed, 04/15/2009 - 12:32
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You can allow stateless on a dhcp server but still hand out default route information. This can be configured at a scope or server level. I've set this up in a lab and it seems to address your original question.

greg.washburn Wed, 04/15/2009 - 12:42
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More correct to say not default route but dns information can be handed out by the dhcp server. The system would then know which router to take.


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