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321

The MAC address might be unique, but there's nothing special about the number that would indicate where it is. MAC 00-00-00-00-00-00 might be on the other side of the planet from 00-00-00-00-00-01. IP is an arbitrary numbering scheme imposed in a hierarchical fashion on a group of computers to logically distinguish them as a group (that's what a subnet is). ...


69

Because the routing tables would become impossibly large. IP addresses are allocated hierarchically, so a router can group routes by address prefixes. The number of autonomous systems present on the net now is reasonable enough to fit in today's hardware. On the other hand, the distribition of MAC addresses across the network is random and completely ...


66

No, they are completely incorrect. In fact, this is a valid IP address: 192.168.24.0 As is 167.23.0.1. Separation of the IP address into dotted segments is a purely human convenience for display. It's a lot easier to remember 192.168.1.42 than 3232235818. What matters to computers is the separation (netmask). It's not valid to have an host address with ...


61

Disclaimer: No offense, but this is a really bad idea. I do not recommend that anyone do this in real life. But if you give a bored IT guy a lab, funny things will happen! For this experiment, I used a Microsoft DNS server running on Server 2012 R2. Because of the complications of hosting a DNS zone in Active Directory, I created a new primary zone named ...


34

The world doesn't run exclusively on ethernet(at least historically). The IP layer is independant of the hardware layer beneath it. PPP nodes don't have Mac addresses. Neither do arcnet, token ring, fddi, hppi. Those other standards may not be as relevent today, but ethernet may be replaced with other technologies in the future and it would be transparent ...


33

It's also reserved for loopback, so no, it's not widely used for anything. In practice, 127.0.0.1 is usually used as "the" loopback address, but the rest of the block should loopback as well, meaning it's just generally not used for anything. (Though, for example, larger Cisco switches will use 127.0.0.xx IPs to listen for attached cards and modules, so at ...


29

Further to the hierarchical routing of IP, having them separate from MAC addresses allows you to change your network card or whole computer while retaining the same IP address (and thus logical network topology). This abstraction allows for much more flexible and maintainable networking.


22

Take a look at the OSI model: http://en.wikipedia.org/wiki/OSI_model This explains why it doesn't make sense to make routing, a layer 3 concept, decisions based on a physical, layer 2, mechanism. Modern networking is broken into many different layers to accomplish your end to end communication. Your network card (what is addressed by the mac address ...


21

Let me show my working here... You need a minimal number of CIDR blocks to cover: 0.0.0.0-9.255.255.255 11.0.0.0-172.15.255.255 172.32.0.0-192.167.255.255 192.169.0.0-223.255.255.255 To turn these ranges into minimal CIDR blocks, you can just use netmask (the swiss army knife of addressing), like so: $ netmask -c 0.0.0.0:9.255.255.255 0.0.0.0/5 ...


19

Simpler IPs a normal human might be able to remember. Less programming, less memory, etc. Familiarity Thousands (millions?) of Network and System Administrators already know it. Existing infrastructure supports it at almost every level already.


18

If you're a network operator, the first step should be IPv6-enabling your network. Talk to your upstream provider(s) about adding IPv6 to your existing service arrangement. If they're not ready or it looks to be too much of a hassle, consider using a tunnel broker. I've had good experience with Hurricane Electric and they will allocate you a /48 and peer ...


17

The two are unrelated. The decisions around how to structure IPV6 are myriad. There's a lot of info at the IPv6 Wikipedia article. Basically, the 128-bit address space of IPv6 gives us such a massive address space that we are unlikely to ever use all of it (2^128 addresses, or 3.4*10^38). The larger address space also allows for a better hierarchical ...


16

To answer the question as it was stated ("how many IPs can a single DNS A record hold?") the answer is very simple: a single A record holds exactly one address. There can however be multiple A records for the same name.


14

Unless I'm misunderstanding, your testers are dead wrong. Valid IP addresses can certainly have a 0 in them.


11

In general: No, it doesn't matter if there is a 0 in the address or not. However, there is a grain of truth in what your testers are saying. In some cases old or broken network equipment will not work correctly on addresses with 0 in the last octests. This is due to the old classfull routing rules. In Classfull routing, you can tell the netmask from the ...


10

Well after a little chat on the IRC the general opinion is that the linux kernel shares some code between ipv4 and ipv6, and that may make completely disabling ipv4 entirely impossible. You can try to compile the kernel without the ipv4 parts but ipv6 may not compile in this case (but nothing keeps you from trying!). You can remove the ipv4 addresses from ...


10

For a truly small company, just wait for your ISP, and anyone else who handles your public face : if you have hosted mail, they should handle any IPv6 matters for mail. If someone hosts your website, ask them if they have made IPv6 DNS entries for you, or what their plan for doing so is. If they say they don't have one, I wouldn't worry about it much this ...


10

@yoonix has sent a link that might have a solution. Link-local, also known as APIPA. 169.254.0.0/16 - This is the "link local" block. As described in RFC3927, it is allocated for communication between hosts on a single link. Hosts obtain these addresses by auto-configuration, such as when a DHCP server cannot be found. If I were your customer, I'd ...


9

I'd be suprised if your ISP didn't offer IPv6 now. Small companies will have the easiest transition so I would get them started now. depending on the home router they have they may or may not have to purchase a new one. http://www.sixxs.net/wiki/Routers is a geat resource to get started on what home routers to look at.


9

Each IPv4 address will take up 16 bytes in the reply. Each IPv6 address will take up 28 bytes in the reply. It is strongly recommended that you ensure the reply will fit in 512 bytes. That would allow for about 25 IPv4 addresses and 14 IPv6 addresses (considering that you need some other information in the packet as well). The exact limit depends on the ...


8

::ffff:0:74.125.226.80 is a dotted-decimal address, and not a real IPv6 address. If you only have full, world-routable IPv6 address (with prefix and a /48) then you cannot communicate with the IPv4 world without a special tunnel. They are for all intents and purposes two different protocols. You have two choices for communication between the two: ...


8

You may well have a "rogue DHCP Server" on the network. The observation that the machines have not detected an IP conflict does not rule a rogue out. See the wikipedia article that I just linked to for a list of tools that can be used to detect if a rogue is on the network or not. Likely some access point has been introduced with its DHCP server turned on. ...


8

In practice, I have seen other 127.0.0.0/8 addresses used in two places: As responses to DNSRBL lookups. Different responses can encode the reason the IP address (or domain) was listed. Wikipedia has some details, as does RFC5782. SORBS list their return codes. Project Honeypot encode data in the three available octets. In the Ubuntu /etc/hosts file. I ...


8

b0fh is right - but also because MAC addresses are not always unique. See for example in virtualization scenarios. Here multiple hosts can serve virtual machines with the same MAC addresses.


8

Can I use NAT to do anything with routing the Domains No, NAT is not aware of DNS. Do I need more public ip addresses You need one IP per server IP:Port tuple. If everything is running on different ports then you could conceivable use the same IP for everything. Just a reminder, IP knows nothing about DNS, and DNS knows nothing about service ports ...


7

FreeBSD (also OS X, and I believe NetBSD & OpenBSD) will respond to requests sent to configured addresses on the loopback interface, just as they would for addresses on any other interface -- If you want an answer you need to assign the address first: mgraziano@monitor ~]$ ifconfig lo0 lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu ...


7

Windows implements RFC 3484 and uses a prefix table to determine which address to use when multiple addresses are available for a name. By default, it favors IPv6 global unicast addresses over IPv4 addresses. You can view/change the prefix policy through netsh: // Open an elevated command prompt // Enter the IPv6 context > netsh int ipv6 // Then use ...


7

Expanding on Zoredache's comment, the only way you're going to get any sort of space in a broker is to DIY it with a VPN/tunnel. A /25 is 128 IPv4 addresses which are a highly valued commodity these days that you are going to pay out the roof for.( Expect 1-2 dollars IP per month atleast) For a block that big you will need to fill out a justification for ...


7

The network is not related to the octets. Octets were substantive many, many years ago - now they're just for readability for us humans. IP addresses are just numbers; representing them as we do is just easier. Try ping 134744072 (which is 8.8.8.8, Google's public DNS server), for instance. The length of the subnet mask is simply a number of bits - a ...


7

Look at the ipconfig /all output. What is it showing as the DHCP server. Is it coming from the router/device you expect? Perhaps you have a rogue DHCP server somewhere.



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