Network Router Security

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Network Router Security

• Packeting Filtering

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OSI Model

1. It is the most commonly refrenced protocol model.
   It provides common ground when describing any
   network protocol.
2. It has seven layers application, presentation,
   session, transport, network, datalink, physical
   layers. Each layer performs a specific function
   and then passes the result on to another layer. A
   sending station passes its data down to the lower
   layers, appending its own information to it. At
   the receiving station, the process happens in
   reverse.

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Network Layer

• 1.It has two basic function Logic network
  addressing, Routing.
• a. Logic network addressing is
  protocol-dependent. It translates logical
  addresses and names into physical addresses
• b. Routing using Routing table of the
  router to control inbound or outbound traffic. It
  also determines which path the data should take
  based on network conditions, priority of service,
  and other factors.
• 2. Packet filtering happens at Network Layer.

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IP addressing

1. It is a Network layer-defined logical address
   through DNS.
2. It takes decimals number from 0 to 255 to
   identify the addresses of the network and the
   host.
3. IP addressing is divided into classes.
4. The subnet and class addressing defines IP
   network address and host address.

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Routing

• 1.A router will maintain a routing table of all
  known networks. It is a multiport device that
  makes decisions on how to direct the data based
  on protocol and network address.
• 2. Router is placed at the borders of a network
  segment.The CRC check is performed to ensure thst
  bad frams are not propagated through out the
  network.
• 3. Router has ability to block broadcast unless
  it is configured to forward all frames.

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Routing-Contiued(example)
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Routing-Contiued

• System B broadcast a route request query to
  system F. Router1 acts as System Bs only
  destination and adds its own MAC address as
  source address and puts Router2s MAC adress in
  its destination field.
• Strips off the header and trailer of the previous
  data beacause new destination address and new CRC
  have been applied to the original data..

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Pocket

1. A packet is a unit of information transmitted as
   a whole from one device to another on a network
2. When the data passes down the OSI model, at each
   layer, information relevant to that layer is
   added to the data. This information is for the
   corresponding layer in the receiving computer to
   reassembles.
3. It has three components Header, Data, Trailer.

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Packet-Contiued

1. Header includes an alter signal to indicate
   that the packet is being transmitted the source
   and destination address clock information to
   synchronize transmission.
2. Data actual data must be broken into chunks to
   fit into packet.
3. Trailer usually contains checking component
   called CRC(Cyclical Redundancy Check).

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Packrt Filtering

• Static packet filtering Controlling access to a
  network by analyzing the incoming and outgoing
  packets and letting them pass or halting them
  based on the IP addresses of the source and
  destination.
• It parse the headers of a packet and then apply
  rules from a simple rule base to determine
  whether to route or drop the packet.

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Packet Filtering-Contiued

• 3. Generally, the header fields that are
  available to the filter are packet type (TCP,
  UDP, etc.), source IP address, destination IP
  address, and destination TCP/UDP port.
• 4.Routing table format
• Action Sour- Port Dest- Port Type
• deny xxx.xxx.xxx.xxx xxx.xxx.xxx.xxx (type)
• allow xxx.xxx.xxx.xxx xxx.xxx.xxx.xxx (type)

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Static packet filtering(example)

• Rule Dir Type SrcAddr DstAddr SrcPort DstPort Act
• A in TCP External Internal gt1024 25
  Permit
• B out TCP Internal External 25 gt 1024
  Permit
• C out TCP Internal External gt1024 25
  Permit
• D in TCP External Internal 25 gt1024
  Permit
• E either any any any any
  any Permit

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Packet Filtering-Contiued

1. Stateful Inspection(Also referred to as dynamic
   packet filtering)It tracks each connection
   traversing all interfaces of the firewall and
   makes sure they are valid.
2. It may examine not just the header information
   but also the contents of the packet up through
   the application layer in order to determine more
   about the packet than just information about its
   source and destination.

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Packet Filtering-Contiued

• 3.It also monitors the state of the connection
  and compiles the information in a state table.
• 4.Unlike static packet filtering, it closes off
  ports until connection to the specific port is
  requested.

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Conclusion

• For static packet filtering, since it is based on
  source IP address, a certain denied IP source
  address can use dynimic IP addressing to bypass a
  router .
• For statefull inspection firewall filtering,
  since it may examine the contents of a packet as
  well, the words contents can be converted into
  graphics to avoid router filtering.