IPv6 Address Assignment Example

Is this the correct answer for the questions regarding: The ISP has given you global prefix 2001:41f0:4060::/48. You have five VLANs that require connectivity. What subnets will you use? Also, for each subnet what IPv6 address will you assign to your default gateway?”

Network ID
2001:41f0:4060:0000::/64
2001:41f0:4060:0001::/64
2001:41f0:4060:0002::/64
2001:41f0:4060:0003::/64
2001:41f0:4060:0004::/64

Default Gateway
2001:41f0:4060:0000::0/64
2001:41f0:4060:0001::1/64
2001:41f0:4060:0002::2/64
2001:41f0:4060:0003::3/64
2001:41f0:4060:0004::4/64

Hi Jeeva,

This looks valid yes. For the subnet you can use anything between 0000 - FFFF in the 4th hextet.

For the default gateway, it might be easier to use ::1 everywhere (first address in the subnet).

Rene

Thank you.

Hi Rene,
Very helpful and clearly explained.
Thank u

Hi Rene,

With reference to the example in your notes, after 2001:41f0:4060:0014::/64 will the subnets go till 2001:41f0:4060:001F::/64 and the next would be 2001:41f0:4060:0020::/64 ? Is this correct?

Thank you.

Hello Srikanth.

The network addresses of the series of subnets starting with 2001:41f0:4060:0014::/64 will follow the following sequence:

2001:41f0:4060:0014::/64
2001:41f0:4060:0015::/64
2001:41f0:4060:0016::/64
..........
..........
2001:41f0:4060:001D::/64
2001:41f0:4060:001E::/64
2001:41f0:4060:001F::/64
2001:41f0:4060:0020::/64
2001:41f0:4060:0021::/64
2001:41f0:4060:0022::/64
2001:41f0:4060:0023::/64
..........

So yes, you are exactly correct.

I hope this has been helpful!

Laz

hello , do we need any licenses to do ipv6 IP assignment and other IPv6 configurations on a cisco router???

Some (older) routers require a feature set for IPv6 yes. You can look them up in the feature navigator.

Rene,
Greetings from Washington, DC. I have question regarding the IPV6 subnets and hosts. Once I determine my subnets as you describe in the lesson do you simply start counting up to find the valid hosts for that subnet? For example, for the network: 2001:41f0:4060:0001::/64, for the first host on this subnet can I simply put in 2001:41f0:4060:0001::1/64 for the first host on this network?

Thanks.

Hello Willie.

You got it, that’s exactly right!

Laz

Hello Willie.

You got it, that’s exactly right!

Laz

19 posts were merged into an existing topic: IPv6 Address Assignment Example

Hi I had a question. we are always told no more than 500 IP addresses in a subnet yet here we have 18,446,744,073,709,551,616.00 IP addresses. whats the idea on how this should be handled?

great IPv6 lesson I’m actually enjoying IPv6 for first time in my studies. in past years I actually cringed learning it now im having fun!

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Hello Brian

Yes, I understand your concern. After spending years (and some of us decades) learning and understanding IPv4 with both its strengths and its limitations, it is very often hard to avoid viewing IPv6 in a similar manner.

Now if you have a prefix length of 48, 64 or even 96 bits which are all very common in IPv6, then of course you will have a subnet capable of supporting an ridiculously enormous number of hosts. Although IPv6 can actually handle a greater number of hosts per subnet than IPv4 (because there are no broadcasts and because it handles addressing differently) it would not be wise to actually use all those addresses.

With IPv4, in order to conserve addresses, we subnetted our scopes to sizes comparable to what we need. With IPv6 you don’t need to do that because there are just so many addresses available there is no concern for address exhaustion. So, in order to simplify addressing, just make all your subnets with a /64 prefix and be done with it. Just don’t actually physically place more than 500 devices within a subnet.

I hope this has been helpful!

Laz

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Hello,
Is any reason that we don’t use subnet 0 in IPv6? I never seen any reference using subnet 0x0000. For example: 2001:41f0:4060:0000::1/64. And I couldn’t find any reason behind this. Is this reserved by any RFC?

Thank you.

Hello Network E

Subnet zero is a valid subnet to use. There is no reason not to use it. It could be that some ISPs prefer not to offer it as it is the first subnet in the series and can be used to refer to blocks of subnets, but that is strictly supposition. There is no technical reason not to use it.

I hope this has been helpful!

Laz

Thank you Lagapides,

I think the explanation in CCNA book is confusing:
Therefore no one answered https://learningnetwork.cisco.com/thread/101127

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Hello Laz,
Just doing some light reading on a Sunday and i came across this. Since there are no broadcast with ipv6 and it handles addressing differently, can a small company say with anywhere between 500 to 1500 nodes just use one ipv6 subnet for their complete network without any performance issues? Just curious.
Thanks,
Cecil

Hello Cecil

This is an excellent question. There’s no clear cut answer :stuck_out_tongue:. It all depends on your network architecture and design. Like you say there are no broadcasts used for IPv6 so in a pure IPv6 environment, you will only have multicast packets being sent. However, keep in mind that any L2 switches in your infrastructure will still “broadcast” those multicast packets out all of their interfaces unless those switches are configured with a feature called Multicast Listener Discovery (MLD) for IPv6. As Cisco documentation describes it, “MLD snooping constrains IPv6 multicast traffic at Layer 2 by configuring Layer 2 LAN ports dynamically to forward IPv6 multicast traffic only to those ports that want to receive it.” More on this feature can be found here.

So, if you employ pure IPv6 in your infrastructure and you enable the MLD feature on all L2 devices, then you can have a more efficient network segment/VLAN. Does that mean that you can employ a subnet of 1500 nodes? The answer is an emphatic “probably”. It also depends on the applications you’re running and the nature of the traffic and the devices on the subnet.

Having said all of this, in general, having smaller subnets is not only beneficial for network efficiency, but also for network organization and security. So even if you can create a subnet with 1500 users without any performance degradation, you would rarely do so, not because of “broadcast problems” but because of security and management issues.

I hope this has been helpful!

Laz

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Hello Laz,
Thanks for the reply.

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