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HDLC/PPP protocol as described is layer 2 protocol.
But I have the confusion of why is this required to be configured on a routers serial interface.
that too when the connection is as below,
Router1----DTE-----SERIAL--------DCE--Router2
Adding more Info: What if this had only switches instead of routers
good fundamental question. HDLC / PPP are certainly layer 2 protocols. I will try to explain why layer two configuration is required on router interface.
What we actually mean when we say that router is layer 3 device?
When we say router is layer 3 device that means it can operate in layer 3 and all layers below it. [I will give you an analogy in real life, when we say the Building has 3 floors means it has floor 1, floor 2 and floor 3]. Same as router works in layer 3 means it operate at maximum on layer 3 but also performs layer 2 and layer 1 functions.
In detail –
When router has a packet to be sent out. It does following action.
A) Layer 3 function
i) Firth will check the network is present in routing table.
ii) If yes, it route the packet to outgoing interface.
Now outgoing interface is having the packet in its queue and need to put on physical channel.
B) Layer 2 function
i) Before sending it on physical channel, router now need to encapsulate the IP packet into a new layer 2 frame, depending on data link in between two router. A frame begins with (frame start) - preamble and delimiter frame. So IP packet can be carried out as a frame on transmission network. Router frames it into PPP or HDLC frame format. The encapsulation should be same on both the routers.
C) Layer 1 function
i) Once the frame is available in cache memory of the interface. Router interface converts it in BITS and transmits it on physical line.
Please feel free if you still have doubts.
Hope that helps
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Transmission Control Protocol and Internet Protocol are two different protocols.
then why they are always mentioned together.
The official name for TCP/IP is Internet Protocol Suite. TCP/IP is a shorthand used by its authors to refer to this new iteration of a standard based on a previous protocol simply called TCP (for Transmission Control Program), so one may infer that the new acronym was meant to differentiate from the latter.
Quoting the Wikipedia entry:
In May 1974 the Institute of Electrical and Electronic Engineers
(IEEE) published a paper titled "A Protocol for Packet Network
Intercommunication." The paper's authors, Vint Cerf and Bob Kahn,
described an internetworking protocol for sharing resources using
packet-switching among the nodes. A central control component of this
model was the Transmission Control Program that incorporated both
connection-oriented links and datagram services between hosts. The
monolithic Transmission Control Program was later divided into a
modular architecture consisting of the Transmission Control Protocol
at the connection-oriented layer and the Internet Protocol at the
internetworking (datagram) layer. The model became known informally as
TCP/IP, although formally it was henceforth called the Internet
Protocol Suite.
Source: http://en.wikipedia.org/wiki/Transmission_Control_Protocol#Historical_origin
They are the protocols used by the Internet Protocol Suite and are always mentioned together because they both are necessary to transmit data over the internet.
From wikipedia: "TCP provides reliable, ordered and error-checked delivery of a stream of octets between programs running on computers connected to a local area network, intranet or the public Internet." and "IP,[...] has the task of delivering packets from the source host to the destination host solely based on the IP addresses in the packet headers."
When you need to send a message from one computer to another the TCP is responsible to break this message in smaller packages and leave the rest of work to IP, that takes care of deliver these smaller groups of data to the correct destination. In the other side, when the other computer receives the packages, TCP assembles them to get the original message.
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What I want to understand is how to determine clients that associated/connected to an AP using network traffic.
For clarification: I am not connected to the network. I am using a usb card on monitor mode and capturing traffic using wireshark. I choose some AP I saw on the traffic and filtered all traffic relevant to it. I am trying to understand, using this data, what clients are connected to this AP.
Hope you guys understand what I mean.
You should look for the association request and association response 802.11 packets in your sniffed list. Basically, client sends the association request and AP replies with the response (you can parse the response according to the 802.11 to find out whether association was granted or rejected. The client will normally be connected to the AP until deauthentication packet arrives from the AP.
From what I know, there's no way to ask the AP for all connected clients unless you are the administrator of the AP but you wouldn't be listenning to the connection wouldn't you ? ;)
However, you can listen to all traffic relevant to this AP and try to determine wheter the captured packet is doing real business (fetching url, ftp, etc.) or just noise. This way, you can safely say that this given IP address is connected to the AP or not.
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It's said in text book that, switches are unable to connect heterogeneous networks (networks with different link layer technology).
However, wireless access point do connects different networks (wireless and wired). Why people say it's a link layer device?
Thanks!
Technically most access points are a bridge. Bridges also operate at the Data-Link layer. A switch is simply a multiport bridge.
They are Data-link layer devices because they use the layer 2 (Data-link) addresses to determine where to forward frames (layer 2 data is called frame, layer 3 data is called packets). More specifically they use the data-link layer address (MAC address for Ethernet) to determine which port the frame should be forwarded.
Any device that operates at one layer also operate at all lower levels. Therefore they can convert from one layer 1 protocol (Ethernet) to another (Wireless).
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Here is the scenery. I have several buildings with same subnet IP addresses (192.168.0.0/24).
I need to secure that connection with OpenVPN.
Please assist me how can I organize VPN connection with IP network 10.10.10.0/24
example
HQ (192.168.0.0/24) - VPN 1 (10.10.10.50) --- VPN 2 (10.10.10.51) - Branch (192.168.0.0/24)
I meas assist with NAT if it will be needed or if I just connect , the C class traffic will just be passed through.
Thank you
Since you are merging two nets, you should use TAP interfaces.
TAP (as in network tap) simulates a link layer device and it operates with layer 2 packets such as Ethernet frames. TUN (as in network TUNnel) simulates a network layer device and it operates with layer 3 packets such as IP packets. TAP is used to create a network bridge, while TUN is used with routing.
This way, you will be joining the HQ network with the branch network like if you plug a (secure, pre-shared key may be ok) ethernet cable between them.
But this will likely crash both environments if they are operating now without knowing one about each other. Maybe the HQ router has the same IP as the branch one, or maybe not, but they are both acting as DHCP servers and now they will be on the same network.
Do you really need to merge both nets? I think you should consider to do some network design and let the HQ on the 192.168.0.0/24 but change the n-th branch to 192.168.n.0/24. Then you can do a TUN OpenVPN setup and route between branches and HQ in a hierachical way. It will save you some bandwith too by not spreading irrelevant broadcast traffic over the tunnel.
Thank you
Well you know, I do not have any router installed in HQ side or anywhere in network and maybe that is a big minus (and I will fix that in a time). Now I just need to secure the links between HQ and branches so the optical network provider (that provides links) could not access out data. If you have any good solution please write.
Thank you
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I understand that a router uses NAT to translate the public IP we get from the ISP to say 300 local IPs. Does a switch perform the same function? If not, how's it different?
No, a switch cannot perform NAT and translate public(s) IP addresses into private addresses.
A switch is a network device that filters and forwards packets between LAN segments. Switches operate at the data link layer (layer 2). So, they are not aware of IP addresses which are network layer (layer 3). A switch keeps a record of the MAC addresses of all the devices connected to it. With this information, a switch can identify which system is sitting on which port. So when a frame is received, it knows exactly which port to send it to, without significantly increasing network response times.
Routers are network devices used to interconnect two different networks (with different IP addressing schemes).