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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 ...


49

blank3's comment on that is mostly right too. The only thing is that you're not saying "all addresses should have access" -- that's done in your firewall(s) and/or the server software and/or other security layers like tcpwrappers. 0.0.0.0, in this context, means "all IP addresses on the local machine" (in fact probably, "all IPv4 addresses on the local ...


46

Is it really that easy for an attacker to forge an IP address in the wild? Sure, if I don't care about actually receiving any responses, I can very easily send out packets using any source address I like. Since many ISPs don't really have good egress rules, anything I forge generally will be delivered. If the attacker actually needs two way ...


44

You need to apply and be granted your own IP allocation by your local registry like RIPE or APNIC. They require annual fees, and you need to justify your requirement (yours is legit). They will assign you an Autonomous System number and a range of IP addresses. You must then find people to peer with (in a datacenter usually), preferably more than one. You ...


42

As stated by many others, IP headers are trivial to forge, as long as one doesn't care about receiving a response. This is why it is mostly seen with UDP, as TCP requires a 3-way handshake. One notable exception is the SYN flood, which uses TCP and attempts to tie up resources on a receiving host; again, as the replies are discarded, the source address does ...


35

Who said that "bulletproof hosting" is expensive? PRQ, the company that hosts thepiratebay.org, offers dedicated servers for less than $200 a month and simple web hosting for $10 a month. From their website: Refugee hosting Our boundless commitment to free speech has been tested and proven over and over again. If it is legal in Sweden, we will ...


34

It doesn't know what device to query. Thus it broadcasts its request to the entire subnet. The DHCP server is listening for a certain type of communication and when it hears that specific broadcast it begins the DHCP conversation with the device that broadcasted its request. Take a look at the DORA process for more information. DORA stands for: D iscovery ...


31

When a service is listening on 0.0.0.0 this means the service is listening on all the configured network interfaces, when listening on 127.0.0.1 the service is only bound to the loopback interface (only available on the local machine)


28

RFC1122, Requirements for Internet Hosts -- Communication Layers, says: { <Network-number>, <Host-number> } (a) { 0, 0 } This host on this network. MUST NOT be sent, except as a source address as part of an initialization procedure by which the host learns its own IP address. See also Section 3.3.6 for a ...


26

/sbin/ifconfig -a


24

As stated in other answers, having too many hosts in the broadcast domain can really start to make broadcasts a mess. They'll need a lot of expansion in the subnet before it becomes a potential problem. Future growth planning becomes a mess. Adding extra sites with their own IP space gets difficult when you've already laid a needlessly huge footprint down ...


24

Unless the ISPs share netblocks (very unlikely), this is not a realistic outcome. If you're looking to keep the static IP for DNS reasons, you should instead lower your TTLs and keep both ISPs (and by extension, IP addresses) until you can gracefully migrate.


23

I don't think they're preferred. I've seen plenty of networks using RFC1918 class A, B, and C addressing schemes. Use the class that suits your needs: How many subnets do you need? How many hosts per subnet do you need? What routing needs do you have to route traffic between subnets? Do you anticipate having a large number of hosts per subnet and want to ...


22

Sometimes it is called "wildcard address", INADDR_ANY, or "unspecified address". The official name is "source address for this host on this network" (RFC 5735, Section 3). It must not appear in packets sent to the network under normal circumstances: This host on this network. MUST NOT be sent, except as a source address as part of an initialization ...


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 ...


21

Unless you own the IP address block it's in, and it's in Provider Independent (PI) Space, then you might be able to switch transit providers, and announce your routes over your new BGP sessions with your new ISP, then it might be possible. Given the lack of networking knowledge show in the OP's question, these assumptions seem unlikely.


21

Little Proof of Concept for Zordeche's Answer (with ubuntu): $ sudo apt-get install hping3 $ sudo hping3 -1 --spoof 11.10.10.20 www.google.com HPING www.google.com (eth0 64.233.169.105): icmp mode set, 28 headers + 0 data bytes Then in another console: $ sudo tcpdump -i eth0 'icmp' tcpdump: verbose output suppressed, use -v or -vv for full protocol ...


19

Use satisfy directive to allow access. 32934 is facebook autonomous system, look facebook ip. satisfy any; allow 66.220.144.0/20; allow 66.220.152.0/21; allow ... deny all; auth_basic "closed site"; auth_basic_user_file conf/htpasswd;


18

The 127/8 network can be used for a number of things. 1) Simulating a large number of different computers in a fast network (simply bring up more interfaces and bind services to them) without using virtual machines. This might be helpful if you wanted to have a number of different web servers running locally on port 80 for some reason. 2) Permitting more ...


17

nmap -sP 192.168.1.0/24 Put your network number in it. It'll do a ping-sweep of your net and report the reverse DNS's of the up machines. Won't find down machines. C:> for /L %N in (1,1,254) do @nslookup 192.168.0.%N >> names.txt That'll do a reverse lookup of every IP in your subnet.


16

The "bulletproof hosting" does not work because of the ISPs reading and evaluating every abuse complaint, but simply because they are throwing every abuse complaint into the bin. This is certainly not expensive and certainly cannot be performed more efficiently if you do it yourself. Apart from that the internet looks quite hierarchic if you do not happen ...


16

The main reason is that stateless address autoconfiguration as per RFC4862 requires a /64 network to work properly. Add to that the assumption that one will want more than a single subnet at one's installation and the difficulty of routing arbitrary multiples of a /64, and the automatic tendency seems to be to assign a /56, or if lazy, a /48. Oddly, I'm ...


15

Looks like 0.0.0.0/8 is in the list of IANA Reserved subnets. http://www.iana.org/assignments/ipv4-address-space/ipv4-address-space.xml, the list of IANA reserved addresses, since this one dates far enough back (1981!) to have been an IANA reserved address range. http://tools.ietf.org/html/rfc5735, describing special uses of IPv4, of which this subnet is a ...


15

Let it be assigned by a DHCP server? if not I would suggest using 192.168.0.250. But DHCP is definitely preferred


15

Your machine is unable to obtain an IP address via DHCP. If you are using a DHCP server on your network you should make sure it has available addresses to distribute. If so, troubleshoot the physical connection between your PC and DHCP server.


14

You can use: /bin/ip addr


14

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


14

IPv4 addresses are not quite so clumsy and random as you would assume. Firstly, an IPv4 address is separated into 4 octets, each ranging from 0 to 255. However, this is not entirely the case as 0 is a reserved number for the network and 255 is reserved for broadcast, which really limits you to 1-254. Secondly, you have to consider that IPv4 addresses are ...


13

If you have an internal address in use, checking curl http://myip.dnsomatic.com might be a good idea on unix shells. Or, just plonk that URL into your browser. If you get a different answer from the "ifconfig -a" result, the ifconfig gave your internal address -- which will probably not work from outside. Even if all seems fine, you could have a ...


13

IP addresses are easy to forge for one-directional UDP traffic. For TCP packets, you can only forge to get a half-open TCP connections with SYN packets. This is the basis of a kind of DOS attack as well. But you can't forge an HTTP connection with a spoofed address (for instance, if you are filtering sessions to use the same IP address). While yes, you can ...



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