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characters/bits... be caferul with the terminology
Lots of errors in this article, which introduces new "myths" instead of removing them.
Really, an article with a so poor quality should have NEVER been featured by TechRepublic.
Of course there are not 128 "characters", but 128 bits. The secion about subnetmask is completely wrong !
And some sentence is completely wrong, such as "the IPv6 loopback address doesn?t even look like a valid address. The loopback address is usually expressed as ::1".
Of course "::1" is a perfectly valid IPv6 address !
And the article speaks about "The domain ip6.arpa is used for reverse hostname resolution.", but it does not show how ! The syntax used in the arpa domain is completely different, and still uses dots between digits (instead of colon), and digits cannot be abbreviated (implied) using a double colon notation. In fact EACH hexadecimal digit has to be written, starting from the left-most (most-significant) in the IPv6 standard non abbreviated notation as the domain, and prepending each hex digit sucessively as a subdomain with a dot separator.
E.g. "2001:BEEF::ABCD" would be resolved in DNS as the domain:
d.c.b.a.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.f.e.e.b.1.0.0.2.ip6.arpa.
This means that recursive inverse resolution will require a lot of requests.
But of course, most reverse resolutions will only need to be performed only the most significant 48-bit prefix, and the most significant 16-bit prefix is generally wellknown in all DNS systems, so they can be queried directly. So an inverse resolution will first query:
b.1.0.0.2.ip6.arpa., then
e.b.1.0.0.2.ip6.arpa., then
e.e.b.1.0.0.2.ip6.arpa., then
f.e.e.b.1.0.0.2.ip6.arpa. ... up to
0.0.0.0.f.e.e.b.1.0.0.2.ip6.arpa.
And inverse resolution will stop there, because after that point, there will generally be no DNS server resolving the rest of the sub-domains reprensenting the low-order digits of the IPv6 address, as they will be assigned only by an ISP which may delegate the full /48 block to a client who has no obligation of running a DNS server. Some ISPs (like providers of IPv6 to IPv4 tunnels or proxies) may subdivide it and will implement an inverse resolution up to the /64 block. But the final 64-bits of the address will almost never be resolved to a domain name, as they will be only within an area of a final client.
Some IPv6 address blocks however have an IPv4-compatible address block, where the first 96 bits are fixed and wellknown, and the final least-significant 32 bits are mapped equally to the 32-bits of an IPv4 address. ONLY This part may still be represented using the wellknown decimal dotted representation (grouping bits by bytes shown in decimal). There's no warranty that any bits after the /64 bits prefix will be mapped this way in any IPv6 address block: clients may allocate their 64-bit addressing space as they want, mapping some parts with IPv4 local addresses if they want, or mapping 48-bit Ethernet addresses of physical interfaces, and creating subdomains (i.e. local subnet mask) as they want (for example when mpaaing hosts on several subnetworks, for example across multiple ISPs, each one with its own local prefix).
The article has then completely forgotten the point of IPv6 : ease of mapping local addresses within a large local addressing space, which will completely deprecate things like NAT and their commplex management rules (notably for managing the address conversion tables). Ipv6 was designed to work automatically on "multihomed" environment, allowing competition and transparency across ISPs and access networks, without having to reconfigure the hosts with complex routing tables.
Finally the statement "Windows does not fully support IPv6" is completely wrong. In fact Windows has been the first to propose a working implementation for IPv6, long before the numerous bugs were corrected in the early Linux distributions (and most of them did not even have one, this had to be manually configured, and did not wotk with LOTS of services).
The author simply forgets the fact that an IPv6 address in its usual notation does not even wualify as a valid domain name. This is also true for using it in URLs, such as HTTP, where the IPv6 address MUST be surrounded between [brackets] to avoid also the confusion with port numbers. The bad thing about IPv6 is in fact its use of colons, instead of dots, but not the fact that it uses hexadecimal (which is good as decimal would have made IPv6 addresses representations much too long).
For this reason, Microsoft had to create a syntax to make the IPv6 address look like a valid domain name. There was no choice only because IPv6's use of the colon was not compatible with the syntax of URLs (remember that Microsoft's approach to networks is based on domain names, but NOT on interface IP addresses, which have never been manageable, also because NOBODY owns any IP address delegation which may change at any time : users are instructed to change their IP mappings, and that's why we have a DNS server in almost all private networks today)
The myth of a "permanent IP address" has been used for too long, and even today, the remaining few IPv4 addresses will like change much more often now that its addressing space is very limited : all ISPs are trying to optimize their own usage and delegations, and are billing IPv4 addresses more than before, to force their clients to count the IPv4 addresses they really need. Almost ALL IPv4 addresses are now very unstable (except for very few core DNS servers in the Internet infrastructure and used to resolve the "root" domain), even for wellknown websites (which are now very frequently accessible through a cloud of proxies offered by CDNs : this is needed for performance as well as security against DDoS because all these proxies are isolating and splitting the access network into multiple areas; this is often needed as well for commercial or legal reasons, to control how Internet clients can connect to some restricted web services, or to help deliver them more targeted advertizing).
Really, an article with a so poor quality should have NEVER been featured by TechRepublic.
Of course there are not 128 "characters", but 128 bits. The secion about subnetmask is completely wrong !
And some sentence is completely wrong, such as "the IPv6 loopback address doesn?t even look like a valid address. The loopback address is usually expressed as ::1".
Of course "::1" is a perfectly valid IPv6 address !
And the article speaks about "The domain ip6.arpa is used for reverse hostname resolution.", but it does not show how ! The syntax used in the arpa domain is completely different, and still uses dots between digits (instead of colon), and digits cannot be abbreviated (implied) using a double colon notation. In fact EACH hexadecimal digit has to be written, starting from the left-most (most-significant) in the IPv6 standard non abbreviated notation as the domain, and prepending each hex digit sucessively as a subdomain with a dot separator.
E.g. "2001:BEEF::ABCD" would be resolved in DNS as the domain:
d.c.b.a.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.f.e.e.b.1.0.0.2.ip6.arpa.
This means that recursive inverse resolution will require a lot of requests.
But of course, most reverse resolutions will only need to be performed only the most significant 48-bit prefix, and the most significant 16-bit prefix is generally wellknown in all DNS systems, so they can be queried directly. So an inverse resolution will first query:
b.1.0.0.2.ip6.arpa., then
e.b.1.0.0.2.ip6.arpa., then
e.e.b.1.0.0.2.ip6.arpa., then
f.e.e.b.1.0.0.2.ip6.arpa. ... up to
0.0.0.0.f.e.e.b.1.0.0.2.ip6.arpa.
And inverse resolution will stop there, because after that point, there will generally be no DNS server resolving the rest of the sub-domains reprensenting the low-order digits of the IPv6 address, as they will be assigned only by an ISP which may delegate the full /48 block to a client who has no obligation of running a DNS server. Some ISPs (like providers of IPv6 to IPv4 tunnels or proxies) may subdivide it and will implement an inverse resolution up to the /64 block. But the final 64-bits of the address will almost never be resolved to a domain name, as they will be only within an area of a final client.
Some IPv6 address blocks however have an IPv4-compatible address block, where the first 96 bits are fixed and wellknown, and the final least-significant 32 bits are mapped equally to the 32-bits of an IPv4 address. ONLY This part may still be represented using the wellknown decimal dotted representation (grouping bits by bytes shown in decimal). There's no warranty that any bits after the /64 bits prefix will be mapped this way in any IPv6 address block: clients may allocate their 64-bit addressing space as they want, mapping some parts with IPv4 local addresses if they want, or mapping 48-bit Ethernet addresses of physical interfaces, and creating subdomains (i.e. local subnet mask) as they want (for example when mpaaing hosts on several subnetworks, for example across multiple ISPs, each one with its own local prefix).
The article has then completely forgotten the point of IPv6 : ease of mapping local addresses within a large local addressing space, which will completely deprecate things like NAT and their commplex management rules (notably for managing the address conversion tables). Ipv6 was designed to work automatically on "multihomed" environment, allowing competition and transparency across ISPs and access networks, without having to reconfigure the hosts with complex routing tables.
Finally the statement "Windows does not fully support IPv6" is completely wrong. In fact Windows has been the first to propose a working implementation for IPv6, long before the numerous bugs were corrected in the early Linux distributions (and most of them did not even have one, this had to be manually configured, and did not wotk with LOTS of services).
The author simply forgets the fact that an IPv6 address in its usual notation does not even wualify as a valid domain name. This is also true for using it in URLs, such as HTTP, where the IPv6 address MUST be surrounded between [brackets] to avoid also the confusion with port numbers. The bad thing about IPv6 is in fact its use of colons, instead of dots, but not the fact that it uses hexadecimal (which is good as decimal would have made IPv6 addresses representations much too long).
For this reason, Microsoft had to create a syntax to make the IPv6 address look like a valid domain name. There was no choice only because IPv6's use of the colon was not compatible with the syntax of URLs (remember that Microsoft's approach to networks is based on domain names, but NOT on interface IP addresses, which have never been manageable, also because NOBODY owns any IP address delegation which may change at any time : users are instructed to change their IP mappings, and that's why we have a DNS server in almost all private networks today)
The myth of a "permanent IP address" has been used for too long, and even today, the remaining few IPv4 addresses will like change much more often now that its addressing space is very limited : all ISPs are trying to optimize their own usage and delegations, and are billing IPv4 addresses more than before, to force their clients to count the IPv4 addresses they really need. Almost ALL IPv4 addresses are now very unstable (except for very few core DNS servers in the Internet infrastructure and used to resolve the "root" domain), even for wellknown websites (which are now very frequently accessible through a cloud of proxies offered by CDNs : this is needed for performance as well as security against DDoS because all these proxies are isolating and splitting the access network into multiple areas; this is often needed as well for commercial or legal reasons, to control how Internet clients can connect to some restricted web services, or to help deliver them more targeted advertizing).
Posted by PhilippeV
26th Oct 2010
