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25

Apart from not getting detailed information about your test setup the main problem seems to be, that you use a message size of 64 byte. This is far away from the usual MTU of 1500 bytes and makes UDP highly inefficient: while TCP merges multiple sends into a single packet on the wire (except if TCP_NODELAY is set) to make efficient use of the link, each UDP ...


15

What do the three rules do? Those 3 rules seem pretty self-explanatory: Reject incoming UDP packets with an ICMP message "port unreachable" Reject incoming TCP packets with "tcp reset" Reject incoming packets (of any other protocol) with ICMP message "protocol unreachable" If you're looking for more detail (about UDP/TCP packets, ICMP), you need to ...


7

Technically, there's no such thing as a "reserved port". In TCP/UDP, the only way to "reserve" a port is to actually bind() a socket to it. A bound port will not be used by other applications; an unused port is, well, unused so other applications are free to use it. If you are writing server software, then you can bind your sockets to specific ports as ...


6

Short answer Yes it is possible, use tsocks nmap -sT IP Long answer First of all Tor doesn't use privoxy, Tor provides an socks proxy for connecting via the Tor network. This means you won't see any network routes or things like that on your system but you have to configure your applications to use the Tor socks proxy to connect via Tor. Typical Tor ...


5

Actually, the above answer is not entirely accurate. The sysctls net.inet.ip.portrange.first and net.inet.ip.portrange.last specify the range of ports the OS can allocate for random ports. You would want to make sure that the range of reserved ports for your application does not fall within these variables. Take a look in the FreeBSD Handbook, section: ...


4

tcpdump usually comes as standard on Linux distros. It will log all packets visible at the server note that you probably want to set it running with a filter for your client IP to cut down on the noise I think this includes packets not accepted by iptables on the local machine - but you might want to test this e.g. /usr/sbin/tcdump -i eth0 -c 3000000 ...


4

I you mean that someone may open 2 TCP connections to your machine, one to port 50505 and another to port 60606, send data on the first one intended to be fed to P and expect to read the output of P from the second TCP connection, then that would be: < /dev/null nc -q -1 -l 50505 | P | nc -l 60606 > /dev/null Or with socat: socat -u ...


3

You could use ZeroConf: http://en.wikipedia.org/wiki/Multicast_DNS Check avahi out: https://help.ubuntu.com/community/HowToZeroconf (ubuntu howto, should be easily adaptable to CentOS)


3

The fact that it says localhost.localdomain connects to localhost.localdomain means that this can't be multicast. Here is a description of multicast in IPv6: http://en.wikipedia.org/wiki/IPv6#Multicasting It would be easier to help you if you describe what you are trying to achieve. Do you want to use multicast, if so for what exactly? Or is your goal to ...


3

Try to increase the maximum block size on the server (e.g. --blocksize 1468). Check with server in debug mode, see if there are retransmits. Check if you really have Gb connection end-to-end. Test on a different client node. Check if there is some other problem not related to tftp - try iperf, tcpdump, ethtool ...


3

I understand that your host, 192.168.2.7 is sending multicast packet to group 239.255.250.250 on port 9131 NOTE: I assume however that servers are listening on port 9131. you didn't provide any info on this. From ifconfig output, I can see that MULTICAST is enabled and the tcpdump confirm this. First make sure that the host running the servers (the one ...


3

As richard already mentioned, what you're looking for has existed for a long time. It's called inetd. There are several implementations of inetd around. Some are simple and do just that socket activation thing (they're usually just the inetd program from some bigger software package containing other basic networking tools, such as GNU inetutils or BusyBox ...


3

You don't want to enable the dgram one. That allows an attacker to make your machine send UDP packets with any content, and if attackers are able to have packets with spoofed source address delivered to you, that means any UDP packet to any destination. For instance if the attacker does: packit -t UDP -s 10.10.10.10 -S 7 -d 10.10.10.11 -D 7 -p ...


2

I don't have a good way to test this right now, but... I believe you can use iptables to translate every port to a single port. It would be something like the following: iptables -t nat -I PREROUTING -m multiport -sports 0:65535 -J DNAT --to-destination 127.0.0.1:1024 That should redirect all incoming ports to 1024. You can then start a server on 1024.


2

The following set of steps were able to resolve the problem: Open a terminal and type: system-config-firewall Enter your password if prompted. Click "Other Ports" on the left-hand side: Click the "Add" button on the right-hand side: Check "User Defined" and enter the values below: Click "OK" and then click the "Apply" button in the toolbar: If you are ...


2

I'm not aware of any expiration policy for IGMP group membership within the Linux stack. It may happen, but I doubt it, since there are at least two ways for the kernel to be told (one explicit, the other implicit) when a program's IGMP membership should be dropped. Therefore, I think you have a bug in the software listening for the multicast packets. (Care ...


2

I saw the same symptom — kernel apparently ignoring IGMP group membership queries from the router — on a CentOS 5 server. I tracked the problem down to a "deny by default" firewall configuration. You, like me, probably didn't sit down and think about IGMP when implementing your firewall. The CentOS system-config-firewall tool doesn't even ask ...


2

Seems that tcpdump is the best, if not the only answer here. It looks perfect for this job. Since, I'm using very limited version of Linux on my NAS, it wasn't there. But simple call to ipkg install tcpdump solved the problem (hopefully I've installed Optware before, as it was also missing). For this particular problem (listening for UDP packets on ports ...


2

Server side: # nc -l -u -p 666 > /tmp/666.txt Other server side's shell: # tail -F /tmp/666.txt | while IFS= read -r line; do echo "$line"; # do what you want. done; Client side: # nc -uv 127.0.0.1 666 #### Print your commands.


2

In principle, modern firewalls are 'stateful'. Meaning you don't need to allow anything from outside as it will find out itself which are the answers to requests that you have made and let them in automatically. So you don't need incoming HTTP or HTTPS, etc. explicitely unless you're hosting a webserver. However, if you have a port forwarding for your ...


2

for upload/download testing i found the iperf tool quite useful: user@hostA: iperf -s user@hostB: iperf -c hostA if the kernel is really the problem, you will usually get a kernel oops before the crash. the main problem is accessing anything the kernel prints to the console, when you are using a graphical interface (and cannot switch to the console ...


2

can some other app also connect to the UDP port and subscribe to the data passing through the port? Port numbers are unique -- e.g. you can't have more than one process open a specific port for listening. However, there's no such limit to the number of connections that can be made to the port. It is up to the one process controlling the port to accept ...


2

NAT port forwarding will redirect the packets rather than duplicate them. In your example, the call traffic should not even arrive at the application layer on B:2222 but be redirected straight to C:3333. You probably want to look at the TEE target for iptables and do the duplication on an intermediate host along the network route from A. C ...


2

The column after local address is "Foreign Address" - as these are UDP ports, and listening ports, there is no foreign address so a wildcard is shown. I'm not sure if this would show the other end(s) if packets had been received as UDP is a connectionless protocol. Also as one-many comms is allowed a single foreign address could be misleading. So it may ...


2

On the client use the IP address of the server that is assigned on the 10 gig interface as your argument to netperf. For example: Server: 1 gig: 192.168.2.1 10 gig: 192.168.3.1 Client: 1 gig: 192.168.2.2 10 gig: 192.168.3.2 From client: netperf -H 192.168.3.1 -l 15


1

To capture traffic, use tcpdump(1) (it has a very extensive set of filtering options to define exactly what to capture, and can save the captured traffic to a file). To read the file, you can use the same tcpdump or the graphical wireshark(1).


1

OS X's nc does have a -u option, which tells it to use UDP. The only tricky thing is that you have to run two instances of nc -u on each terminal, one sending and one listening; and since one (generally the listener) will be in the background, using control-C to exit it will only exit for foreground instance; you have to kill the background one explicitly. ...


1

If it says 0.0.0.0 on the Local Address column, it means that port is listening on all 'network interfaces' (i.e. your computer, your modem(s) and your network card(s))


1

Apparently there was a problem with logging. I set the dns server to log to rsyslog. While stracing, the file descriptor for syslog didn't seem to 'work'. Solved by making bind log to local file: logging{ channel bindlog { file "/var/log/named/bind.log" versions 3 size 5m; severity info; print-time yes; print-severity yes; ...


1

If you can tell the black-box program to listen only on a specific IP address, you could bind it to an arbitrary loopback address, like 127.0.0.10, and then use netcat, AKA, nc, to pipe between the port on 127.0.0.10 and whatever you like on the outside IP. There's an article on Netcat in wikipedia with a section about proxying. You'll want to understand ...



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