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Security of network infrastructure and network traffic. For questions about security of network equipment, topology, protocols, traffic, administration, and configuration. Related tags: [packet], [firewall], [network-scanners], [network-access-control].

4
votes
To block URL, the router must work at the HTTP level; on the DNS, only server names and IP addresses are exchanged. You need a transparent HTTP proxy which automatically hijacks connections, recogniz …
answered Apr 21 '13 by Thomas Pornin
9
votes
Flooding the CAM table to force the switch to fall back to hub behavior (broadcasting all packets to all ports) is an "attack" only if you consider the normal switch behavior (sending the packet only …
answered May 6 '11 by Thomas Pornin
7
votes
The anonymity provided by Tor stems for the large number of cooperating nodes; a "private Tor network" looks like ultimate counterproductivity. Wait, no, a private Tor with peer authentication is …
answered Jun 8 '11 by Thomas Pornin
2
votes
with OS including a lot of undocumented elements and activities, some of which implying network activity, in particular listening to incoming requests on some port and thus offering a service to … policy. Your external hardware firewall will trap all activity which goes through it but it may not see activity related to the local network (and Windows systems do that a lot, with all the NetBIOS …
answered Aug 9 '13 by Thomas Pornin
12
votes
Many sites use private addressing inside their network, and the router runs NAT so that outgoing connections are feasible. The NAT thing implies, by construction, the same effect than a firewall … which would prevent any incoming connection from the outer world to one of the machines in the inner network. When you enable IPv6, inner machines become externally visible. So you'd better setup …
answered Jun 10 '11 by Thomas Pornin
1
vote
RC4 has a few shortcomings: It has no Initialization Vector distinct from the key. If you use the same key twice, then you get twice the same sequence of pseudo-random bytes, and using that is a dea …
answered Jan 3 '13 by Thomas Pornin
12
votes
frame), it dispatches it on all the other links. This is inconvenient in large networks, because this means that when two machines talk to each other, they monopolize the whole network. To avoid this … issue, switches try to remember which machine is on which link, so that they may propagate a given frame only on the relevant link, thus leaving most of the network free for other simultaneous …
answered Nov 7 '11 by Thomas Pornin
8
votes
Usually, each machine on which the mail transits: adds a Received: header stating from where the email seems to come; announces its name (which could be an IP address) to the next machine, which may …
answered Oct 7 '11 by Thomas Pornin
8
votes
I suppose that our situation is the following: you have detected some undesirable network traffic and you are looking for the perpetrator, so as to, more or less metaphorically, convey to him the … inherent unwisdom of his villainous behaviour. The source address of the offending IP packets points to a college; the college uses Network Address Translation so that outgoing traffic from all their …
answered Sep 6 '12 by Thomas Pornin
4
votes
You have to make a distinction between the applicative protocol and the transport protocol. SSL/TLS is a transport protocol: it ensures some security-related guarantees (confidentiality, integrity, so …
answered Apr 14 '14 by Thomas Pornin
7
votes
Writing your own encryption is never a good idea. Even trained cryptographers (I mean people who have studied the subject for years, have a big shining diploma [a PhD] to say it, and, more importantly …
answered Jul 11 '11 by Thomas Pornin
15
votes
MAC addresses are supposed to be unique worldwide, so that no two devices use the same MAC address. This matters when several devices are on the same link: if two devices have the same MAC address, th …
answered Sep 6 '11 by Thomas Pornin
2
votes
RDP stands for "Remote Desktop Protocol", so what it provides to people who connect is a full fledged session on the server. By default, this gives these people the same kind of power that they could …
answered Feb 19 '13 by Thomas Pornin
18
votes
session key over an already exchanged master key; the abbreviated handshake uses only symmetric cryptography and requires less network exchanges. A point which is worth noting is that in a full …
answered May 23 '11 by Thomas Pornin
2
votes
Password meters (like the sites you may find) are not good at measuring password entropy, despite what they claim. Human beings are not good either at producing entropy. Entropy (in this context) is a …
answered Nov 9 '12 by Thomas Pornin

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