Hot answers tagged

107

Because the proper HTTP Host header is often required to actually get the intended site. It's very common to host multiple web sites on the same IP address and distinguish between them based on the HTTP Host header specified by the client (as well as the TLS SNI value nowadays in the case of HTTPS). That is, when you entered http://example.com into your ...


102

These are dynamically configured link-local addresses. They are only valid on a single network segment and are not to be routed. Of particular note, 169.254.169.254 is used in Amazon EC2 and other cloud computing platforms to distribute metadata to cloud instances.


98

To block 116.10.191.* addresses: $ sudo iptables -A INPUT -s 116.10.191.0/24 -j DROP To block 116.10.*.* addresses: $ sudo iptables -A INPUT -s 116.10.0.0/16 -j DROP To block 116.*.*.* addresses: $ sudo iptables -A INPUT -s 116.0.0.0/8 -j DROP But be careful what you block using this method. You don't want to prevent legitmate traffic from reaching the ...


96

From the command line you could use: sudo nmap -sS -p 22 192.168.10.0/24 Substitute for the local address space on your network. I sometimes use this when I plug in a headless rasberry pi and want to find where to ssh to.


68

The TTL get decremented when it pass through a router. This makes sure that if the packet is traveling around in circles it will eventually die. The TTL field of an IP v4 packet is an 8-bit field (255 decimal). So setting it high at the start it isn't a big deal since it can't actually be that large in a well-formed packet (Although, some things might ...


63

:: can be used once in an IPv6 address to replace a consecutive blocks of zeroes. It can be any length of zeroes as long as it is greater than a single block. All zeroes in a single block can be represented by :0: instead of writing out all four zeroes. In this case, it means all zeroes, or the IPv6 equivalent of the IPv4 0.0.0.0 As an example of something ...


59

What you're seeing is the Google proxy address. Mobile users with a chrome browser (either Android or iOS) that have the bandwidth management features turned on will often be seen as using one of these addresses as the requester as described here. In essence the data you're serving is being requested by the Google Data Compression Proxy, optimized and sent ...


51

You can't bind to more than one IP address, but you can bind to all available IP addresses instead. If so, just use 0.0.0.0 for a binding address in your MySQL configuration file (e.g. /etc/mysql/my.cnf) as follows: bind-address = 0.0.0.0 If the address is 0.0.0.0, the server accepts TCP/IP connections on all server host IPv4 interfaces. Furthermore if ...


45

Assigning more than one IP address to one hostname is also possible: rr.example.com. A 192.0.2.12 rr.example.com. A 192.0.2.23 rr.example.com. A 192.0.2.34 rr.example.com. A 192.0.2.45 When you query a DNS server for rr.example.com you'll get back a list of IP addresses back. You can then choose to connect to ...


44

Chrome is interpreting the number 1168951531 as a decimal number, which when represented in hexadecimal is 45ACC8EB. 45ACC8EB in hex is the same as the dotted decimal 69.172.200.235, when you take each pair of hex digits as one decimal number. 45 -> 69 AC -> 172 C8 -> 200 EB -> 235 Short answer: It's the pure decimal representation of the same ...


43

That behavior is actually due to a normal feature of ping and has no relation to your actual hardware. Indeed, prefixing the IP address (or part of it) with a leading zero will cause the number to be interpreted as octal. So 057 means 57 in base 8 which is 47. Thus ping will send the ICMP query to the machine located at address 10.10.208.47 and therefore ...


41

59.224.XX.178.d is not an IP-address but a hostname, or rather part of it. Last tries to do a reverse lookup and stores both the resulting hostname and ip-address for the remote host. By default the hostname gets displayed and long ones get truncated to display nice columns. Try last -a to display the hostname on the last column without truncation. or ...


39

Any well-behaved device on an Ethernet LAN is free to ignore nearly any traffic, so PINGs, port scans, and the like are all unreliable. Devices are not, however, free to ignore ARP requests, afaik. Given that you specify you're scanning a local network, I find the least-fragile method of doing what you want is to try to connect to a remote address, then ...


37

nmap -p 22 --open -sV 192.168.178.0/24


35

Yes, it is possible for multiple hostnames to use the same ip address, the best practise is to use a CNAME record to point to the A record bar.example.com. CNAME foo.example.com. foo.example.com. A 192.0.2.23 Take note of all the full stops. Having one hostname to represent multiple ip addresses is a little more complicated. If we are ...


32

The main advantage of using DHCP reservations is that the assignment of a "static" IP address is managed centrally. This can be helpful for example if you are often rebuilding a particular computer or constantly changing the OS or if setting a "static" IP address is cumbersome (DirectTV DVR for example). Using DHCP reservations is also handy if you ever ...


31

The port is a part of the layer 4 protocol in use - TCP or UDP, for the most part; it's not related to the memory addressing of the actual computers, so don't get confused by the 32 or 64 bit memory addressing of modern operating systems. The headers of these layer 4 protocols have specifically defined structures, for which exactly 16 bits are used for the ...


29

Is that how IPv6 is intended to work? In short, yes. One of the primary reasons for increasing the address space so drastically with IPv6 is to get rid of band-aid technologies like NAT and make network routing simpler. But don't confuse the concept of a public address and a publicly accessible host. There will still be "internal" servers that are not ...


28

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.


26

As others mentioned, the security group for your EC2 instance may not allow the HTTP port. First,find the Security Group your instance is using. Then, under Network & Security, go to the Security Groups section. Select your instance's security group and add an Inbound Custom TCP rule for Port range 80.


26

If an elastic IP is associated with an EC2 instance, that's the instance's external IP. You can demonstrate this by doing curl canhazip.com in the command line.


25

Firewall it off. iptables -A OUTPUT -m owner ! --uid-owner root -d 169.254.169.254 -j DROP This rule prohibits any user other than the root user from opening connections to 169.254.169.254.


25

They are saying that one is the broadcast, one is the net base, and 2 are usable by the customer. Sounds like you are getting a /30 block. Just to get a better understanding, check out the authoritative thread on IP subnetting. How does IPv4 Subnetting Work?


25

Probably they are using Google data compression proxy (https://developer.chrome.com/multidevice/data-compression). And to answer your question (from the same page): As a site owner, how do I perform IP geo-targeting? The IP address of the mobile device is forwarded to the destination server via the X-Forwarded-For header. Site owners should ...


24

To me, the terms mean different things. A floating IP address is used to support failover in a high-availability cluster. The cluster is configured such that only the active member of the cluster "owns" or responds to that IP address at any given time. Should the active member fail, then "ownership" of the floating IP address would be transferred to a ...


24

The Order, Deny, and Allow options have been replaced in Apache 2.4 with <Directory /var/www/mysite.com/htdocs/public> Require all granted </Directory> You can explicitly restrict addresses through the use of the following: <Directory /var/www/mysite.com/htdocs/public> Require all granted Require not ip 192.168.0.1 </...


23

In windows you can add a route based on the interface without knowing the gateway by passing 0.0.0.0 as gateway this gives something like this: route add <IPtoRoute> mask <MaskOfTheIp> 0.0.0.0 IF <InterfaceNumber> route add 203.0.113.9 mask 255.255.255.255 0.0.0.0 IF 2


23

You can get the user's IP address directly if you simply serve the site over HTTPS. You probably should be doing this anyway - especially since you mentioned these are login and registration pages. Quoting from the Data compression Proxy page mentioned in other answers: Is my secure traffic optimized by the compression proxy? No, data compression proxy ...


22

This means you will get a /30 network for you to use. If you have a network (lets say 192.168.0.0/30), possible addresses are: 192.168.0.0 <- this is your network ID, unusable for 'normal' traffic 192.168.0.1 <- 1st usable IP 192.168.0.2 <- 2nd usable IP 192.168.0.3 <- broadcast address, unusable for 'normal' traffic So you basically get 4 ...


22

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.


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