The BSCI exam and CCNP certification requires that you be well versed in the basics of IP Version 6, or IPv6. If you're new to IPv6, you'll quickly learn that it's not exactly just two more octets slapped onto an IPv4 address! IPv6 addresses are quite long, but there are two ways to acceptably shorten IPv6 address expression. To pass the BSCI exam, become a CCNP, and get that all-important understanding of IPv6, you've got to understand these different methods of expressing an IPv6 address. My last IPv6 tutorial discussed zero compression; today we'll take a look at leading zero compression.
Leading zero compression allows us to drop the leading zeroes from every field in the address. Where we could only use zero compression once in an IPv6 address expression, leading zero compression can be used as often as is appropriate. The key with leading zero compression is that there must be at least one number left in each field, even if that remaining number is a zero.
You sometimes see books or websites refer to leading zero compression as "dropping zeroes and replacing them with a colon", but that explanation can be a little confusing, since the blocks are separated with a colon to begin with. You're not really replacing the leading zeroes, you're dropping them.
Let's look at an example of leading zero compression. Taking the address 1234:0000:1234:0000:1234:0000:1234:0123, we have four different fields that have leading zeroes. The address could be written out as it is, or drop the leading zeroes.
Original format: 1234:0000:1234:0000:1234:0000:0123:1234
With leading zero compression: 1234:0:1234:0:1234:0:123:1234
There's no problem with using zero compression and leading zero compression in the same address, as shown here:
Original format: 1111:0000:0000:1234:0011:0022:0033:0044
With zero and leading zero compression: 1111::1234:11:22:33:44
Zero compression uses the double-colon to replace the second and third block of numbers, which were all zeroes; leading zero compression replaced the "00" at the beginning of each of the last four blocks. Just be careful and take your time with both zero compression and leading zero compression and you'll do well on the exam and in the real world. The keys to success here are remembering that you can only use zero compression once in a single address, and that while leading zero compression can be used as often as needed, at least one number must remain in each field, even if that number is a zero.
Showing posts with label 6. Show all posts
Showing posts with label 6. Show all posts
Thursday, December 25, 2008
Cisco CCNP / BSCI Exam Tutorial: IP Version 6 Zero Compression
BSCI exam success is all part of becoming a CCNP, and part of that success is now learning the basics of IP Version 6, or IPv6. One of the most difficult parts of learning IPv6 concepts is the radically different addressing scheme that IPv6 uses as compared to IPv4. Just look at these sample addresses:
Typical IPv4 address: 129.14.12.200
Typical IPv6 address: 1029:9183:81AE:0000:0000:0AC1:2143:019B
As you can see, IPv6 isn't exactly just tacking two more octets onto an IPv4 address!
I haven't met too many networkers who really like typing, particularly numbers. You'll be happy to know there are some rules that will shorten those addresses a bit, and it's a very good idea to be fluent with these rules for your exam.
You remember from your CCNA studies that there's no difference between an upper-case letter and lower-case letter in hexadecimal. That's one of three basic rules you need to know when working with IPv6 addressing. The other factors deal with all the zeroes you'll run into in IPv6 addresses! One of these rules is the rule of zero compression.
The rule of zero compression states that if an address contains consecutive fields of zeroes, they can be expressed with two colons. It doesn't matter if you have two fields or eight, you can simply type two colons and that will represent all of them. The key here is that you can only do this once in an IPv6 address. This is referred to as zero compression. Here's an example:
Original format: 1234:1234:0000:0000:0000:0000:3456:3434
Using zero compression: 1234:1234::3456:3434
Again, you must remember that you can only do this once in an IPv6 address expression.
What if there are zeroes in the address that don't quite fit this rule? The next part of our IPv6 tutorial will deal with leading zero compression, another tool you can use to shorten these long, long addresses!
Typical IPv4 address: 129.14.12.200
Typical IPv6 address: 1029:9183:81AE:0000:0000:0AC1:2143:019B
As you can see, IPv6 isn't exactly just tacking two more octets onto an IPv4 address!
I haven't met too many networkers who really like typing, particularly numbers. You'll be happy to know there are some rules that will shorten those addresses a bit, and it's a very good idea to be fluent with these rules for your exam.
You remember from your CCNA studies that there's no difference between an upper-case letter and lower-case letter in hexadecimal. That's one of three basic rules you need to know when working with IPv6 addressing. The other factors deal with all the zeroes you'll run into in IPv6 addresses! One of these rules is the rule of zero compression.
The rule of zero compression states that if an address contains consecutive fields of zeroes, they can be expressed with two colons. It doesn't matter if you have two fields or eight, you can simply type two colons and that will represent all of them. The key here is that you can only do this once in an IPv6 address. This is referred to as zero compression. Here's an example:
Original format: 1234:1234:0000:0000:0000:0000:3456:3434
Using zero compression: 1234:1234::3456:3434
Again, you must remember that you can only do this once in an IPv6 address expression.
What if there are zeroes in the address that don't quite fit this rule? The next part of our IPv6 tutorial will deal with leading zero compression, another tool you can use to shorten these long, long addresses!
Cisco CCNP / BSCI Exam Tutorial: A Guide To Ipv6 Addressing
Learning IPv6 is paramount in your efforts to pass the BSCI exam and go on to earn your CCNP, and it's going to help in your real-world networking career as well. IPv6 can be confusing at first, but it's like anything else in Cisco or networking as a whole - learn one part at a time, master the fundamentals, and you're on your way to success. In today's article we're going to take a look at IPv6 address types.
In IPv4, a unicast address is simply an address used to represent a single host, where multicast addresses represent a group of hosts and broadcasts represent all hosts.
In IPv6, it's not quite that simple. There are actually different types of unicast addresses, each with its own separate function. This allows IPv6 to get data where it's supposed to go quicker than IPv4 while conserving router resources.
IPv6 offers two kinds of local addresses, link-local and site-local. Site-local addresses allow devices in the same organization, or site, to exchange data. Site-local addresses are IPv6's equivalent to IPv4's private address classes, since hosts using them are able to communicate with each other throughout the organization, but these addresses cannot be used to reach Internet hosts.
Site-local and link-local addresses are actually derived from a host's MAC address. Therefore, if HostA has HostB's IPv6 address, HostA can determine HostB's MAC address from that, making ARP unnecessary.
Link-local addresses have a smaller scope than site-local. Link-local addresses are just that, local to a physical link. These particular addresses are not used at all in forwarding data. One use for these addresses is Neighbor Discovery, which is IPv6's answer to ARP.
You can identify these and other IPv6 addresses by their initial bits:
001 - Global address
(first 96 bits set to zero) - IPv4-compatible address
1111 1111 – Multicast
1111 1110 11 - Site local
1111 1110 10 - Link Local
As a future CCNP, you're more than familiar with the reserved IPv4 address classes. You also know that they're not exactly contiguous. The developers of IPv6 took a structured approach to IPv6 reserved addresses - any address that begins with "0000 0000" is an IPv6 reserved address. One of these is the IPv6 loopback address, and this will give you some practice with your zero compression!
IP v6 Loopback: 0000:0000:0000:0000:0000:0000:0000:0001
Using Leading Zero Compression Only: 0:0:0:0:0:0:0:1
Combining Leading Zero and Zero Compression: ::1
Zero compression looks pretty good now, doesn't it? You just have to get used to it and keep the rules in mind. You can use all the leading zero compression you want, but zero compression ("double-colon") can only be used once in a single address.
IPv6 is here to stay, not only on your BSCI and CCNP exams, but in the real world as well. Learning it now will not only aid you in passing your Cisco exams, but in supporting IPv6 in the future.
In IPv4, a unicast address is simply an address used to represent a single host, where multicast addresses represent a group of hosts and broadcasts represent all hosts.
In IPv6, it's not quite that simple. There are actually different types of unicast addresses, each with its own separate function. This allows IPv6 to get data where it's supposed to go quicker than IPv4 while conserving router resources.
IPv6 offers two kinds of local addresses, link-local and site-local. Site-local addresses allow devices in the same organization, or site, to exchange data. Site-local addresses are IPv6's equivalent to IPv4's private address classes, since hosts using them are able to communicate with each other throughout the organization, but these addresses cannot be used to reach Internet hosts.
Site-local and link-local addresses are actually derived from a host's MAC address. Therefore, if HostA has HostB's IPv6 address, HostA can determine HostB's MAC address from that, making ARP unnecessary.
Link-local addresses have a smaller scope than site-local. Link-local addresses are just that, local to a physical link. These particular addresses are not used at all in forwarding data. One use for these addresses is Neighbor Discovery, which is IPv6's answer to ARP.
You can identify these and other IPv6 addresses by their initial bits:
001 - Global address
(first 96 bits set to zero) - IPv4-compatible address
1111 1111 – Multicast
1111 1110 11 - Site local
1111 1110 10 - Link Local
As a future CCNP, you're more than familiar with the reserved IPv4 address classes. You also know that they're not exactly contiguous. The developers of IPv6 took a structured approach to IPv6 reserved addresses - any address that begins with "0000 0000" is an IPv6 reserved address. One of these is the IPv6 loopback address, and this will give you some practice with your zero compression!
IP v6 Loopback: 0000:0000:0000:0000:0000:0000:0000:0001
Using Leading Zero Compression Only: 0:0:0:0:0:0:0:1
Combining Leading Zero and Zero Compression: ::1
Zero compression looks pretty good now, doesn't it? You just have to get used to it and keep the rules in mind. You can use all the leading zero compression you want, but zero compression ("double-colon") can only be used once in a single address.
IPv6 is here to stay, not only on your BSCI and CCNP exams, but in the real world as well. Learning it now will not only aid you in passing your Cisco exams, but in supporting IPv6 in the future.
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