13 votes
Accepted

pinging broadcast address

Not all machines will answer a broadcast ping. (all broadcast -- 255.255.255.255, or subnet broadcast -- eg. x.x.x.255) Some see it as a "security feature", because one could spoof the origin to flood ...
  • 29.8k
9 votes
Accepted

Why traceroute is still Used?

Traceroute doesn't give inexact information, it performs tests in a specific way and give some results based on the response it receives (or do not receive). You have to know how to interpret the ...
  • 18.5k
7 votes
Accepted

What are the key advantages and disadvantages of NDP compared to ARP?

As Michael Hampton points out, ND does a great deal more than IPv4 ARP, but I will answer from the perspective of simply resolving a layer-2 address from a layer-3 address (ARP function). ARP ...
  • 94.6k
7 votes
Accepted

Is this computer a threat? On same network range, but in a workgroup

The situation you describe is very similar to what cost Target* many millions of dollars when its network was hacked, and customer information was stolen. Never let another company have something ...
  • 94.6k
6 votes
Accepted

I can't ping the other router using OSPF protocol, Why?

(I imagine your setup to be something like this) Your OSPF adjacency is not coming up because the IP addresses on the facing interfaces between R1 and R2 are not in the same subnet. As soon as you ...
6 votes
Accepted

What is persistent connection and session

First a word about: I understand word persistent as following : no one else can occupy wire at the time of persistent connection. So this connection is only one-to-one. But this is not right. ...
  • 18.5k
6 votes

Cant ping & access HP switch on network connected on trunking mode

(Disclaimer: I am not familiar with HP switches, so I wont' be able to give proper command syntax for show/display commands). For a first, let's leave all routing discussion aside. AS5500 an AS3100 ...
6 votes
Accepted

Understanding how devices on a LAN/VLAN discover the existence of other local devices

This is an actual problem. Most often, one hosts "wants" something from the other host, so it'll try to connect via a known DNS name. In a company network, a DNS server provides the IP address for a ...
  • 72.8k
6 votes

Juniper SRX answers all ping requests instead of forwarding

The session output shows that the box is translating the destination address 10.5.5.22 to 10.41.22.3 and then routing it out ae0.22 instead of ae0.5 like you'd expect. It is very likely that your NAT ...
5 votes
Accepted

How come my gateway have different subnet ip

The subnet mask is 255.255.240.0 which means 20 bits belong to Network and remaining 12 is for host. The range of IP Address inside the network can be found by running your IP address against Subnet ...
  • 207
4 votes

Is it possible to brute force search/guess symmetric NAT port prediction for hole punching?

"The literatures says that because NA and NB randomly assign external ports anytime their respective clients initiate a new connection (even if the destination address is the same) the external port ...
4 votes
Accepted

Is it possible to brute force search/guess symmetric NAT port prediction for hole punching?

why is it not possible for clients A and B to try the external port information provided by S Because the ports used for talking to S will never be the ports used to talk to either endpoint. A->S ...
  • 29.8k
4 votes
Accepted

Manual setting MTU still needed today?

Path MTU Discovery works by sending packets of various sizes to a target with the DF (Don't Fragment" bit turned on. If a router in the path has a smaller MTU, its behavior should be to send back an ...
  • 14.1k
4 votes
Accepted

How would I track down what port a device is on remotely?

This is exactly the process I would use in most circumstances. If you have CDP (Cisco Discovery Protocol) enabled on all your switches though, you can save a LOT of time by running Cisco's MAC ...
4 votes
Accepted

Cant ping & access HP switch on network connected on trunking mode

You should check the portal server limitations, since it is enabled on A5500 Vlan 1 interface: # interface Vlan-interface1 ip address 172.16.1.1 255.255.255.0 portal server 1 method layer3 # While ...
4 votes

Given a network switch, can we identify the devices (IP not assigned yet) connected to it?

If you can get the server to generate some traffic, you can determine the manufacturer of the NIC card from the OUI portion of the MAC address. That isn't the same as the server manufacturer, but ...
  • 63.5k
4 votes
Accepted

Network topology discovery with Flows

The problem with looking at flows is that you only see the source and destination, and nothing in between. Also, you only see flows that exist at the time you capture data. There may be other ...
  • 63.5k
4 votes

How does a host know the ip addresses of other hosts on the same LAN?

But say two hosts are connect in a LAN, how does host A know that B exist and that B has the ip address, say, 192.168.0.6? Simply put, the application tells it so, either by specifying the address or ...
  • 63.5k
3 votes
Accepted

Change device - Reassign static IP

You'd need to know the MAC address of the newly plugged in printer beforehand. Then you could reserve a specific IP address for that MAC address through DHCP Reservation. Note that that's not the ...
  • 264
3 votes
Accepted

Get details of device connected to a network

You can find the vendor of the NIC from the OUI database.
3 votes
Accepted

IOS tools to discover a network

a very very useful GUI tool from Cisco called Cisco Network Assistance can help you to discover the entire network with all details you need to know about it.where you can discover your network ...
  • 3,424
3 votes
Accepted

What happen underneath when I manually change my IP address?

Wouldn't there be a chance that two people under the same subnet enter the same IP address and they go into confict? How to prevent them ? Yes, that can, and does, happen when networks have manually ...
  • 94.6k
3 votes
Accepted

tracert command return Request timed out

Extract from Microsoft Support How to Use TRACERT to Troubleshoot TCP/IP Problems in Windows The TRACERT diagnostic utility determines the route to a destination by sending Internet Control ...
  • 18.5k
3 votes
Accepted

Find all printer on the network

Most of (any?) network printers can be joined on TCP port 9100, so you can use NMAP (or other suitable software) to scan for all hosts with this port opened on all your networks.
  • 18.5k
3 votes

GHOST servers or devices in Vulnerability scan report

We can't help you with your management tool. However, you can track down an unknown IP address in your network by examining the ARP tables of connecting devices, routers, ... and looking for the ...
  • 72.8k
3 votes

Understanding how devices on a LAN/VLAN discover the existence of other local devices

One possible way (by far not the only one) is mDNS based Service Discovery as per Zeroconf Networking, based on link-local multicast (see Zac67's statement) and the DNS domain .local. For a good ...
3 votes

How to detect passive network host?

You can slow Nmap's discovery way down, so it won't disturb fragile equipment. First do a simple ping sweep. You can go very slow, taking hours (or days) if need be. Once you know the active ...
  • 63.5k
3 votes

How does a host know the ip addresses of other hosts on the same LAN?

But ARP seem to take an ip address as input and give the corresponding MAC address. That is correct (for IPv4). ARP can also be used to check if an IP address is already in use (for DHCP, Zeroconf, ...
  • 72.8k
3 votes
Accepted

How my neighbour machines in the same network knows my interface ip?

Simple answer: The machines don't know the route. The IP address that you use must be in the range of the so-called "subnet" the machine belongs to. This means that all machines that can be reached ...

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