Broadcast

[SDK]

In a normal subnet of 192.168.1.* with a subnet mask of 255.255.255.0, the broadcast address should be 192.168.1.255. I'm trying to ping my network using my this address without succes. Why?

Where can I find a program that will brodcast a ping or a TCP Port? If you answer me Nmap, please tell the command line or a page where I can find the information! Thank.

[MrLinus]

What are the devices on the network? Generally using ping 192.168.1.255 -t (windows) or ping 192.168.1.255 -b (linux) should work unless ping is surpressed by router/switch/firewall.

And I'm not sure what you mean by broadcasting a ping or a TCP port. No TCP port can be broadcast so to speak. If you mean broadcasting a ping to a TCP port, IIRC, ICMP is a protocol on it's own and doesn't go to a specific port.

[SDK]

Ping 192.168.1.255 -t doesn't work either. I get Request timed out. I'm sure that my Switch doesn't block me because I have a program that do a Broadcast and that work. I'm trying to make this program work across VPN/Subnet and I'm unable so that why I'm looking for a utilites to do the same to locate the problem. The first step is to be find that program and make it work since my own subnet.

[MrLinus]

Have you run arp -a after the ping broadcast just to see if anything is actually being picked up after the fact? What kind of VPN is it? If it's a router-to-router setup, is it possible that one is blocking it? (my gut says something is blocking). Have you done a sniff of the network to see what/where packets are going and other activity that might be going on?

[SDK]

I'm pretty sure the VPN is blocking the broadcast. But I'm also sure that the broadcast is NOT block in my local subnet. Right now, I only want to be able to broadcast a ping or an UDP port inside my local subnet. After I'm able to do that, I'll attack myself to get the broadcast work across the VPN.

[SirDice]

192.168.1.255 is a subnet broadcast. 255.255.255.255 is a broadcast address.

What OSs are there on that subnet? If it consists of windows only machines you'll never get a response. A Windows machine will not respond to a broadcast ping (by default). A linux machine may respond depending on the configuration (read: distro). Both have the option to turn it on or off.

Please note: You should make sure it's turned off. If it's turned on your network is vulnerable to a smurf attack.

As for nmap, try nmap -sP -vv -n 192.168.1.255

Originally posted here by MsMittens
No TCP port can be broadcast so to speak.

Try and send a SYN packet to 192.168.1.255/port 80 i.e. and see what happens..not sure what should though..

nmap -sS -vv -n -p80 -P0 192.168.1.255 should do the trick.

[SDK]

Can I broadcast over a UDP port? Will I get answer from service listening over that port?

I try doing a nmap -sU -p***** -v -P0 255.255.255.255

Starting nmap 3.75 ( http://www.insecure.org/nmap ) at 2004-11-04 10:31 Eastern
Standard Time
Initiating UDP Scan against 255.255.255.255 [1 port] at 10:31
The UDP Scan took 2.06s to scan 1 total ports.
Host 255.255.255.255 appears to be up ... good.
Interesting ports on 255.255.255.255:
PORT STATE SERVICE
*****/udp open|filtered unknown

Nmap run completed -- 1 IP address (1 host up) scanned in 2.235 seconds

[MrLinus]

nmap -sS -vv -n -p80 -P0 192.168.1.255

I would have thought that it would have been more like nmap -sS -vv -n -p80 -P0 192.168.1.0/24 sent out over the network rather than the broadcast to get all hosts to respond to a probe of port 80.

Perhaps someone should get TH13's opinion?

[SirDice]

If there's something listening, it's highly probably that it'll respond.
It might be a good idea to keep a sniffer running when doing these scans.
It'll give you more detailed information on what's happening.

nmap -sS -vv -n -p80 -P0 192.168.1.0/24

That would scan all addresses in the 192.168.1.0-192.168.1.255 range.
It would be the same as using 192.168.1.*

[SDK]

I try those command and both work

nmap -sU -p42508 -P0 -S 192.168.1.18 -vv 192.168.1.1-10

nmap -sU -p42508 -P0 -S 192.168.1.18 -vv 192.168.2.50-65

Does I need the answer to this question : Can I broadcast over a UDP port? If yes, how?

What I find stranage also is doing a nmap -sU -p42508 -P0 -S 192.168.1.18 -vv 255.255.255.255 only return me one host. This, I don't understand at all.