Ipv6 eui-64

(sumant S) #1

Can you please explain me the following points:-

1>When you use EUI-64 on an interface that doesn’t have a MAC address then the router will select the MAC address of the lowest numbered interface on the router.

2>from the article I understood that Eui 64 generates the interface Id for link local and global Unicast addresses.What about the unique local addresses.can we generate the interface Id using Eui 64 for unique local addresses?


(Lazaros Agapides) #2

Hello Sumant

Just so others can follow, this question pertains to the following lesson:

Some layer two technologies, such as serial connections on a router, do not have MAC addresses. This means that the EUI-64 process cannot be used to obtain an IPv6 address for that interface. In such a case, the router will use the MAC address of the interface with the lowest number. For example, on a router with interfaces Gi0/0, 0/1, 0/2 and 0/3, the MAC address of Gi0/0 will be used to configure the IPv6 address of the serial interface using EUI-64 as it is the lowest numbered interface.

Link local addresses are assigned using various techniques depending on the vendor, operating system etc of each device. One of the methods is indeed to use the EUI-64 process. As for global unicast addresses, the lesson does indeed show you how to configure them using the EUI-64 technique. Now I’m not sure what you mean by unique local addresses. There are only link local and global unicast. There are no other IPv6 addresses that can be assigned to a host. Can you clarify your question?

I hope this has been helpful!


(sumant S) #3

Hi Laz

Thanks for taking the time to reply.My question is can we apply unique local IPV6 addresses to host and internal interface(lan side)of router and we could do nat translation for unique local address to global unicast address the same wah we do in ipv4.
I know we have plenty of global unicast addresses that we do not need to worry about nat for ipv6.i am just curious to know how we can make use of unique local unicast addresses???

Thanks a lot again for your wonderful explanations as always.


(Lazaros Agapides) #4

Hell Sumant

Thanks for your kind words! I do my best to be as clear and understandable as possible.

Concerning your question, yes it is possible to apply NAT to unique local IPv6 addresses and translate them to global unicast addresses. In order to do so we would employ NAT66, that is Network Address Translation IPv6 to IPv6. This functions exactly the same way as NAT for IPv4, by translating the IPv6 address as well as manipulating the transport layer ports in order to allow PAT. Now although this is possible, it is not very desirable as you stated as well, because we have the appropriate address space to assign each and every internal device with a global unicast address. However, a better alternative to NAT66 is NPTv6.

IPv6-to-IPv6 Network Prefix Translation or NPTv6 isa feature that allows for the translation of IPv6 addresses from one subnet to another without the requirement to rewrite the transport layer headers. This readuces the load on network devices and also does not interfere with the encryption of the full IP payload. This is a huge improvement to traditional NAT because it avoids many of the problems that NAT traditionally introduced into networking. To find out more about NPTv6 take a look at the following Cisco link.

Essentially, the use of these addresses is that you are free to use them on any internal network without the need to for centralised registration. If you start using global unicast addresses on your devices and you allow them to connect directly to the Internet, (without any kind of translation mechanisms) the local ISP will not necessarily route those addresses because they are not registered to you. You can still use them if you use a translation mechanism so the actual address doesn’t appear on the Internet itself, but what if your destination on the Internet just happens to be the same as the IPv6 address you gave to a host on your network (highly unlikely, but possible nonetheless). By using the unique local addresses with a translation mechanism such as NPTv6, you can assign addresses internally as you like while creating the appropriate translation to get on the Internet without fear of conflicting addresses.

I hope this has been helpful!


(sumant S) #5

Hi Laz
Thanks for reply.i was just going with dhcpv6 configurations both stateful and stateless.i know in slaac the interface I’d is created using Eui-64 but is it true for stateful auto configuration when the client get ipv6 prefix from dhcpv6 server.does it pad ff and fe and invert the 7th bit in case of dhcpv6 a signed address.
In the lesson I could not see ff and fe padded when the client receives ipv6 prefix from dhcpv6 server…


(Lazaros Agapides) #6

Hello Sumant.

Take a look at this lesson:

At the beginning, it shows the FF and FE and the inverted 7th bit. Take a look at this screenshot:

Review the lesson and if you need any more information, just let us know!

I hope this has been helpful!