CCDA/CCDP - IPv6 hope it helps

Author

IPv6 hope it helps

gaulz

2003-08-31, 7:24 pm

Hi,

I too am studying for 861. I was fortunate enough to have been put on the course, so I wil do my best to explain aggregation for you. The way I explain is inexact, but will help get you through (I hope)

The address space is aggregated (or broken up) into 6 fields:

*Global identifier -3 bits
##(This is basically a country code)
*TLA -13 bits
##(Top level assignment)
--This where IP addresses are issued from
--( eg IANA, etc)
*Reserved -8 bits
##For testing expansion etc
*NLA -24 bits
##(Next level aggregator)
--this field can be broken up, deneding on
--the heichy of address issue.
(will explain more later on in post)
*SLA -8 bits
(Site local address)
*Interface ID/MAC address -64 bits

Now for the fun stuff..........

Any data will have the mac address appended to the end of the IPv6 address space.

The examples below are only for encapsulation. nce again these are inexact, but should help.

If the destination is on a segment that does not need routing, the only field used will be thw SLA. This field will have have the address FE80. [FE80 signifies this packet will not be routed]

If the destination is still within the private (company) network, but needs to be routed, the only field used will be the SLA, however the address in the SLA field will be FEC0. [FEC0 signifies the packet will be routed, but will not enter the public network.

If 2 hosts within an ISP need to communicate, the packet needs to go into the public network, so the MAC address is added, the SLA field now contains the specific site specific address for the originating network.

If A host in Australia needs to communicate with a host in Fiji, the mac address is appended, the SLA is set to the specific network, the ISP address is added in the NLA space. The IANA equivilant in Australia will have a unique identifier, and this is entered in the TLA field (address space). The country code for the host's country is added to the end of the address.

In IPv6 you only need the information that is essential to pass the packet.

Note 1:
the address FE80 is a LINK LOCAL address. It is actually at the very beginning of the address. The MAC address is at the end. All other bits are Zero (0).

Note 2:
Th address FEC0 is a SITE-Local address. It is also place at the start of the address space. The mac adress is at the end. 16 bits before the MAC address is a subnet field. I think this is used as per v4, but am not 100%. All other bits are 0

Note 3:
NLA's can be heirachical, and consist of more then 1 NLA. If there is a major telco (telly1) that distributes a large amount of addresses to a second company (bigboy2), and bigboy 2 then issues a small amount of addresses to a local ISP (Bob3), the address space will look like this:

|Global|TLA|Telly1|bigboy2|bob
3 |SLA|Mac |
| NLA1 | NLA2 |NLA3 |
|No more then 24 bits|

Please remeber that this is inexact and is only a reference for how to think of IPv6 addres space. If anyone can see anything wrong with what I say or has any better ideas, please post

Thanks

gaulz

2003-08-31, 7:31 pm

The address space will only look like the above post if there is a collision.

The ipv6 adderss space:

==============================
===
Global Identifier 3 bits
==============================
===
TLA (Iana etc) 13 bits
==============================
===
Reserved 8 bits
==============================
===
NLA _____________________24 bits
Telly 1
_____________________
Bigboy 2
_____________________
Bob 3
_____________________
==============================
===
SLA 16 bits
==============================
===
Interface ID/Mac address 64 bits
==============================
===

ahuebel2

2003-10-15, 6:28 pm

so what would you call a private address in IPv6? Would it be a link-local (local use) address or a site-local address?

OHCCNP2003

2003-10-20, 12:22 am

Site-Local Unicast Addresses are pretty much like IPv4 private addresses.

Link-Local is used to connect devices on the same local link network without having to use global addresses. Look at neighbor discovery protocol and stateless autoconfiguration for a better explanation. I went over this for the 642-871 exam, but don't remember all of the details.

psimon

2003-12-10, 3:27 pm

I am a little confused with the first part of this thread.

In the description of the IPv6 address you mention that the first 3 bits are the global indentifier, something like a country code. I am not sure that this can be the case at all, for a start, with only three bits to play with you will only have 2**3 combinations = 8.

Now my understanding is that the first 3 bits are the format prefix. Now depending on how the prefix is set, will determine the type of address.

For a Aggregatable global unicast address as described above, the first three bits would be set as 001 (or 2/3 in Hex / prefix). Now the rest of the address would follow the rules outlined earlier in the thread, that is 13bits TLA, 8bits reserved, 24bits NLA, 16bits SLA and 64bits Interface ID.
The important point to note, is that if this is an aggregatable global unicast address the first 3 bits will not change from 001.

When you have an IPv6 Link-Local address or Site-Local address (IPv4 private address equivalence), the structure of the address format changes considerably.

Link Local

the address format is FE80::/64 This means that the address will always start with FE80 or 1111111010 followed by 54 0's. The remaining 64bits will be the interface identifier.

Site Local

the address format FEC0::/48 This means that the address will always start with FEC0 or 11111111011 followed by 38 0's then 16bits for the local subnet and 64 bits for the Interface identifier.

Not sure whether this clarifies things or just muddy's the water even further.

davidbec

2003-12-12, 6:57 pm

For the exam you will need to know something else.

The TLA is divided into two parts. The
IR (Internet Registries) and the sub-TLA. The NLA follows the sub-TLA.

The IANA assigns the numbers to the IR, who assigns numbers to the sub-TLA.

This is an actual exam question.

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