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Webcast-Catalyst9k
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Defining the Site ID configuration in IPv6

Hello,

  I was reading thread #17232 (e.g. IPv6 Subnetting - Overview and Case Study) which provides a great example on how to subnet an enterprise network.

  One question that I am struggling to understand is how the author was listing options for defining the Site ID configuration in IPv6.  Apparently, there were three Options presented (e.g. A,B, and C).

The question revolves around Option A. 

  Apparently, in Option A, one has the ability to configure 4 sites, 4 sub-sites, 4096 subnets by using the first 2 bits for the site, the next two bits for the sub-site, and the next three nibbles for the subnets.

How does one have the ability to split an existing nibble if each character in an IPv6 address represents a 4 bit boundary (e.g. in this case 2 bits allocated for the Site ID and the last 2 bits in the 4 bit boundary for sub-sites)?

Is there anyway someone can show the same example, BUT incoporate Option A (first 2 bits for the site, next two bits for sub-site)?  How does one actually configure the Site addresses splitting the nibble between the site and subsite ID within an existing 4 bit boundary?  Please advise. 

Thanks.

Wes

5 REPLIES
New Member

Re: Defining the Site ID configuration in IPv6

Just to provide more information, it appears that  if I take the following IPv6 example and break down just the hexadecimal portion of the subnet area into bits I get the following:

2001:db8:1234:0000::/64

                          |

                         \/    

           0000 0000 0000 0000

Also, if using just the first 2 bits for the Site ID it looks like I can configure four possible scenarios like so:

          0000 0000 0000 0000

           0100 0000 0000 0000

           1000 0000 0000 0000

           1100 0000 0000 0000

Also, the next 2 bits for the SubSite ID can also be configured with the four scenarios possible:

           0000 0000 0000 0000

           0001 0000 0000 0000

           0010 0000 0000 0000

           0011 0000 0000 0000

However, one can not convert the first two bits into a Hexadecimal address by itself. 

One would have take the entire nibble (2 bits for Site ID and 2 bits for Sub-Site) combine them both in order to successfully configure it into a complete hexadecimal address like shown below.

  So it would look something like the following:

          0000 0000 0000 0000

          0010 0000 0000 0000

          1001 0000 0000 0000

          1111 0000 0000 0000

          .....  (Or some derivation of the above in multiple combinations)

  So taking the deviations shown above, and popping it back into the IPv6 example address would be perhaps something like so?

                           0000 0000 0000 0000

                                     |

                                    \/

              2001:db8:1234:0000::/64

                           0001 0000 0000 0000

                                     |

                                    \/

              2001:db8:1234:1000::/64

                           1010 0000 0000 0000

                                     |

                                    \/

              2001:db8:1234:A000::/64

                           1111 0000 0000 F000

                                     |

                                    \/

              2001:db8:1234:F000::/64

*Honestly, just by looking at the IPv6 address, it is extremely difficult to figure out just by looking at the subnet portion of the hexadecimal address (nibble) how many sites and subsites are configured just by eyeballing it.  Also, how does the router differentiate it as well?

How does one look at the IPv6 addresses above and ultimately differentiate whether the IPV6 address above is intentially using the first 2 bits or the entire nibblet (4 bits) for the site address. 

Ontop of that, there are the subnet addresses following it making it even more unbearable to sit through and figure this out. 

Please advise.  Thanks.

Regards,

Wes

Re: Defining the Site ID configuration in IPv6

Please provide the link to the treath

Looking for some Networking Assistance? 
Contact me directly at jcarvaja@laguiadelnetworking.com

I will fix your problem ASAP.

Cheers,

Julio Carvajal Segura
http://laguiadelnetworking.com

Julio Carvajal
Senior Network Security and Core Specialist
CCIE #42930, 2xCCNP, JNCIP-SEC
New Member

Re: Defining the Site ID configuration in IPv6

Hi Julio,

   Please see thread below:

https://supportforums.cisco.com/docs/DOC-17232

Re: Defining the Site ID configuration in IPv6

Hello Wes,

Hmmm let me try to see how to explain IPv6 subnetting.

I did a training not long time ago about IPv6 so here is what my presentation had about IPv6.

IPv6 Subnetting

•It is common to receive from the ISP’s at least a  /48 IPv6 prefix

•So we can have up to 2^80 bits to manipulat
•RFC 4291 recommends to use a /64 as the minimum prefix(Stateless autoconfiguration {EUI-64})
•We have 16 bits in order to subnet ( half of the IPv4 address space)

So now, let's work with an example:

In our scenario we as Company Julio S.A requested an IPv6 prefix to our local ISP(they provided us the prefix of 3001:a981:1234::/48)

We are planning to have in C.R

  • 16 Different Sites
  • Each site will have 16 sub-sites
  • and Each sub-site will have up to 256 IPv6 prefix (subnets)

So far we have the following information

  1. 16 bits to play and subnet (more than 65000 addresses)
  2. We know the exact amount of addresses we need

First Step:

How many bits do we need to cover the sites, sub-sites, subnets

2^x = 16  4

2^x=16     4

2 ^x = 256 8

So we have 4 bits to play with the site ID, 4 bits to play with the subsite and 8 bits to play with the Subnet ID

Second Step

Start using the binary calculation

3001:a981:1234:0000/64

Each of the 0's is equivalent to 4  bits so we need one for the site Id, One for the subsite and the other 2 for the subnet ID.

3001:a981:1234:0000::/48

Site IDs

0000

0001

0010

0011

0100

0101

0111..You get the point

The first available IPv6 Site would be

3001:a981:1234:0000:/52

Second one

3001:a981:1234:1/52

And keeps going till you reach the 16 Site ID prefix.

Now let's get the sub-site ID from the  3001:a981:1234:1/52 Site ID.

Processure will be the same just that now we will focus on the second hex value

so

3001:a981:1234:1000

Sub-Site

0000

0001

0010

0011

0100

0101

0111..You get the point


The Subsite Zero prefix will be

3001:a981:1234:1000::/56

And you will do the same for the Subnet range.

Is it clear now?

Looking for some Networking Assistance? 
Contact me directly at jcarvaja@laguiadelnetworking.com

I will fix your problem ASAP.

Cheers,

Julio Carvajal Segura
http://laguiadelnetworking.com

Julio Carvajal
Senior Network Security and Core Specialist
CCIE #42930, 2xCCNP, JNCIP-SEC
New Member

Re: Defining the Site ID configuration in IPv6

Julio,

   Thanks.  Yes that makes sense.

   If you don't mind, lets also explore what happens with Option A.  Lets say

Company Julio S.A requested an IPv6 prefix to our local ISP with a different set of requirements

How many bits do we need to cover the sites, sub-sites, subnets

2^x = 4  2

2^x=  4   2

2 ^x = 4096 12

and they provided us with a prefix as shown below:

2001:db8:abcd::/48

I believe we would have to configure a /50 prefix boundary like so below which will give us four Site address:

2001:db8:abcd:0000::/50

2001:db8:abcd:4000::/50

2001:db8:abcd:8000::/50

2001:db8:abcd:C000::/50

Below is how I came up with it:

Then, to figure out the subsites, I took the next 2 bits of the nibble and came up with the four subsites like so for Site 0:

Subsites for Site 1:

Subsites for Site 2:

Subsites for Site 3:

Regards,

Wes

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