Someone has to add a route manually if he wants to use one with this IP address. noprefixroute: Do not create a route in the route table when this IP address is added.dynamic: The IP address is lost when the interface goes down.scope global: The IP address is valid everywhere on this network.brd 192.168.4.255: The broadcast address for this subnet.An eight-bit binary number equates to 255 therefore, the subnet mask is 255.255.255.0. The “/24” tells us there are 24 contiguous leading bits set to one in the subnet mask. link/ether: The MAC address of the interface.qlen 1000: The maximum length of the transmission queue.group default: This interface is in the “default” interface group.state UP: The interface is operational and connected.qdisc fq_codel: The scheduler is using a discipline called “Fair Queuing, Controlled Delay.” It’s designed to provide a fair share of the bandwidth to all the traffic flows that use the queue.mtu 1500: The maximum transfer unit this interface supports.The hardware layer of the network (layer one) is also UP. : This interface supports broad- and multicasting, and the interface is UP (operational and connected).The “en” stands for ethernet, “p0” is the bus number of the ethernet card, and “s3” is the slot number. enp0s3: The network interface name as a string.The physical interface is more interesting, as we’ll show below: inet6: The IP version 6 address, scope, valid_lft, and preferred_lft.This should never be larger than the valid_lft value. For an IP version 4 IP address allocated by DHCP, this is the amount of time the IP address can be used with no restrictions. For an IP version 4 IP address allocated by Dynamic Host Configuration Protocol (DHCP), this is the length of time the IP address is considered valid and able to make and accept connection requests. lo: The interface with which this IP address is associated.This IP address is only valid inside the computer (the “host”). Eight bits set to one represents 255 in binary, so the subnet mask is 255.0.0.0. The part of the address after the forward-slash ( /) is Classless Inter-Domain Routing notation (CIDR) representing the subnet mask. It indicates how many leading contiguous bits are set to one in the subnet mask. The value of eight means eight bits. link/loopback: The media access control (MAC) address of the interface.qlen 1000: The maximum length of the transmission queue.The default is to place them all in a group called “default.” group default: Interfaces can be grouped logically.state UNKNOWN: This can be DOWN (the network interface is not operational), UNKNOWN (the network interface is operational but nothing is connected), or UP (the network is operational and there is a connection).The noqueue discipline means “send instantly, don’t queue.” This is the default qdisc discipline for virtual devices, such as the loopback address. There are different queuing techniques called disciplines. It schedules the transmission of packets. qdisc noqueue: A qdisc is a queuing mechanism.This is the size of the largest chunk of data this interface can transmit. The physical networking layer (layer one) is also up. lo: The network interface name as a string.If you do not want to allow IP address containing e.g.Let’s break down all the information we received: If you know you’ll never get such strings, then you can use the expression above otherwise:īy: \(25\|2\|\|\) In your file, it will be matched although it is not a valid IP address (each part of the IP address cannot exceed 255). Of course if you have something like: 999.888.777.666 So we can represent it this way: grep '\$'. An IP address is basically a dot separated sequence of 4 numbers each having 1 to 3 digits. Now if you want to search for lines containing IP addresses, you’ll need to use some regular expressions. So we need to match 188.194.233.1 only using a whole word matching: grep -w 18.194.233.1 /var/log/auth.log Unfortunately it might return more than expected: 118.194.233.1 and 18.194.233.14 also match. Here are a few commands I use for this.įirst if you want to search for an IP address in a log file, you can just use grep: grep 18.194.233.1 /var/log/auth.log I very often have to either find log entries related to a specific IP address or just find IP addresses in a log file or process a file containing IP addresses and other things.
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