Semester 1 v3'1'1: Networking Basics

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Semester 1 v3.1.1Networking Basics

• MODULE 10
• Routing Fundamentals and Subnets

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Basics of Routed Protocols

• Routed protocols enable routers to forward data
  between networks.
• Protocols can be routable provided a logical
  addressing scheme is provided.
• Addresses split into network and host portions.
• Routed protocols employ subnet masks to
  differentiate network portion from host portion.

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Delivering on Services

• End-to-end delivery services are either
  connectionless, or connection-oriented.
• Connection-oriented protocols establish a virtual
  link between hosts before transmission occurs.
• Packets travel sequentially down a single path
  through a circuit-switched network.
• Connectionless protocols do not establish a
  virtual link before communication.
• Packets are sent sequentially, but travel down
  different paths through packet-switched
  network.
• Packets are re-assembled at destination.

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Caution Routers at Work

• Routers are important to networking
• Determines next hop for incoming packets to take,
  based on directly connected networks.
• Maintains routing table to so that it and other
  routers are aware of current network topology.
• Routing tables help determine most efficient path
  for packets to take to their destination.
• Maintains ARP tables to ensure a smooth handoff
  of data to bridges, switches, and end-user
  devices on the destination network.

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Routing vs. Switching

• Routing and switching are similar concepts, but
  are in different layers
• Routing occurs in Layer 3, uses IP.
• Maintains routing tables (IP network addresses)
• Maintains ARP tables (IP/MAC addresses)
• Switching occurs in Layer 2, uses MAC.
• Maintains bridging tables (MAC addresses)

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Routed vs. Routing Protocols

• Routed protocol data can be forwarded across
  router interfaces using their Layer 3 addressing
  scheme.
• IP Internet Protocol
• Novell IPX Internetwork Packet eXchange
• AppleTalk
• Routing protocols are how routers communicate
  with each other, to determine paths and share
  routing tables.
• RIP Routing Information Protocol
• IGRP Interior Gateway Routing Protocol
• OSPF Open Shortest Path First

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Routing Static vs. Dynamic

• Routing table entries are crucial for effective
  path determination. Routes can be learnt, or set
  manually.
• Static routing
• Administrator manually enters all routes.
• Suitable for small networks.
• No unnecessary routing updates means less
  traffic.
• Becomes a problem if a link goes down.
• Dynamic routing
• Routers learn the topology from neighbours.
• Quick to adapt to changing topologies.
• Works well if a link goes down.
• Has greater overheads than static routing more
  routing updates means more network traffic.

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Routing Protocol Principles

• The algorithm that the protocol is based on is
  usually designed with these in mind
• Ability to select best route in shortest time.
• Efficiency through simplicity.
• Stable, yet flexible.
• Rapid convergence, where all routers running the
  same routing protocol agree on available routes
  in as little time as possible.
• A routing protocols ability to determine best
  path for any given packet relies on the metrics
  the protocol uses for path determination
• Bandwidth Maximum theoretical capacity of a data
  link.
• Delay End-to-end packet travel time.
• Load Activity experienced on the adjacent link
  or next router.
• Reliability Error rate of a link.
• Hop count Number of waypoint routers to
  destination.
• Ticks Delay on a data link using x86 PC clock
  ticks.
• Cost Manually assigned custom value

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Routing Inside and Out

• Collective networks can be defined to be
  administered as one domain an autonomous
  system.
• Routing within autonomous systems is performed by
  Interior Gateway Protocols (IGPs)
• RIP Routing Information Protocol
• IGRP Interior Gateway Routing Protocol
• OSPF Open Shortest Path First
• Exterior Gateway Protocols (EGPs), such as Border
  Gateway Protocol (BGP) are used to route data
  between autonomous systems.

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Interior Gateway Protocols

• Distance-vector IGPs
• Usually measures distance as number of hops to
  destination router.
• Knows the general direction vector of any
  near link on the internetwork.
• Sends periodic routing updates to neighbouring
  routers.
• A routers network perspective relies on the
  perspective of its neighbours.
• Link-state IGPs
• Only sends routing updates when trigged by
  changes in network topology.
• Uses Link-State Advertisement (LSA) floods for
  rapid convergence.

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Subnets? Who Needs Them?

• Subnets make large networks more manageable by
  splitting them up into separate logical networks.
• Logical address space made more efficient.
• Subnetting results in few wasted IP addresses.
• If a network is not subnetted, then no bits have
  been borrowed from host field yet.
• Class A default netmask 255.0.0.0 (/8)
• Class B default netmask 255.255.0.0 (/16)
• Class C default netmask 255.255.255.0 (/24)

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How to use Subnet Masks

• We would like to identify the network portion of
  the host IP address 138.25.12.130, where the
  subnet mask is 255.255.255.0.
• Convert the IP address to binary, and its subnet
  mask 255.255.255.0 to binary.
• The binary 1s in the subnet mask indicate the
  network portion of the host IP address, and the
  binary 0s indicate the host portion of the host
  IP address.
• So we already know the length of the network
  portion, but wed like to identify what the
  network portion is.
• Now perform a Boolean AND operation on the binary
  host IP address and subnet mask. This is how the
  subnet mask determines what network the host IP
  address resides on.
• 10001010.00011001.00001100.10000010 ? Host IP
  address 138.25.12.130
• 11111111.11111111.11111111.00000000 ? Subnet
  Mask 255.255.255.0
• -------------------------------------------------
  -----------------------
• 10001010.00011001.00001100.00000000 ? Network IP
  address
• Convert the binary network portion into decimal,
  so you can read it P
• The network portion is 138.25.12.0. This is
  referred to as the network address, or the
  network that the host IP address 138.25.12.130
  resides on.

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How to use Subnet Masks

• Now try to identify the network portion of the
  host IP address 138.25.12.130, where the subnet
  mask is 255.255.255.248.
• Convert the IP address to binary, and its subnet
  mask 255.255.255.248 to binary.
• The binary 1s in the subnet mask indicate the
  network portion of the host IP address, and the
  binary 0s indicate the host portion of the host
  IP address.
• So we already know the length of the network
  portion, but wed like to identify what the
  network portion is.
• Now perform a Boolean AND operation on the binary
  host IP address and subnet mask. This is how the
  subnet mask determines what network the host IP
  address resides on.
• 10001010.00011001.00001100.10000010 ? Host IP
  address 138.25.12.130
• 11111111.11111111.11111111.11111000 ? Subnet
  Mask 255.255.255.248
• -------------------------------------------------
  -----------------------
• 10001010.00011001.00001100.10000000 ? Network IP
  address
• Convert the binary network portion into decimal,
  so you can read it P
• The network portion is 138.25.12.128. This is
  referred to as the network address, or the
  network that the host IP address 138.25.12.130
  resides on.

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Steps to Subnet Sublimely

• Work out the class and default subnet mask of the
  network given. (Table below is Class C)
• Calculate number of bits to be borrowed.
• For x bits borrowed, we get 2x 2 usable
  subnets. The first and last subnets are unusable.
• For y bits left in the host field, we get 2y 2
  usable hosts. The first and last host addresses
  are unusable.
• Unusable networks/host addresses are for network
  and broadcast purposes.

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Steps to Subnet Sublimely

• Calculate the subnet mask.
• For x bits borrowed, add together their combined
  bit-value to the default subnet mask for its
  class.
• Calculate the subnet IDs.
• Increment subnet portion one bit at a time.

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Subnetting Step 1

• Create 1000 usable subnets, given the network IP
  address 165.10.0.0.
• Work out the class and default subnet mask of the
  network given.
• Class B network, default Subnet Mask 255.255.0.0
• In binary, the subnet mask looks like this
• 11111111.11111111.00000000.00000000
• Expressed in bit-values, the subnet mask is
  calculated using the following
• 27 26 25 24 23 22 21 20 . 27 26
  25 24 23 22 21 20 . 27 26 25 24
  23 22 21 20 . 27 26 25 24 23 22
  21 20

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Subnetting Step 2

• Calculate number of bits to be borrowed.
• For x bits borrowed, we get 2x 2 usable
  subnets.
• Since we want 1000 usable subnets, then 2x 2
  1000, then 2x 1002
• Next power of 2 is 1024, so x 10. Therefore we
  need to borrow 10 bits to create at least 1000
  usable subnets.

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Subnetting Step 3

• Calculate the subnet mask.
• For x bits borrowed, add together their combined
  bit-value to the default subnet mask for its
  class.
• The new subnet mask in binary looks like this
• 11111111.11111111.11111111.11000000
• The 10 bits weve borrowed can also be expressed
  as borrowing an entire octet, plus an additional
  2 bits. The notation for the new subnet mask
  expressed in bit-values is
• 27 26 25 24 23 22 21 20 . 27 26
  25 24 23 22 21 20 . 27 26 25 24
  23 22 21 20 . 27 26 25 24 23 22
  21 20
• New Subnet Mask 255.255.255.192

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Subnetting Step 4

• Calculate the subnet IDs.
• Increment subnet portion one bit at a time.
• Recall that new subnet mask of 255.255.255.192
  was calculated after borrowing 10 bits from host
  portion
• Octets 3 and 4 are shown below in binary to
  highlight bit changes
• Subnet 0 - 165.10.0000000.00000000 165.10.0.0
• Subnet 1 - 165.10.0000000.01000000 165.10.0.64
• Subnet 2 - 165.10.0000000.10000000
  165.10.0.128
• Subnet 3 - 165.10.0000000.11000000
  165.10.0.192
• Subnet 4 - 165.10.0000001.00000000 165.10.1.0
• Subnet 5 - 165.10.0000001.01000000 165.10.1.64
• Subnet 6 - 165.10.0000001.10000000
  165.10.1.128
• Subnet 7 - 165.10.0000001.11000000
  165.10.1.192
• Subnet 8 - 165.10.0000010.00000000 165.10.2.0
• Subnet 9 - 165.10.0000010.01000000 165.10.2.64
• Subnet 10 - 165.10.0000010.10000000
  165.10.2.128
• ... etc.

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Welcome to my world )

• Daniel Comarmond
• CCNP, CCDP, CCSP, CCAI
• Cisco Networking Academy Instructor
• Systems Engineer Cisco Systems
• E-Mail dcom_at_it.uts.edu.au
• MSN dcom82_at_dcom82.com
• Phone [phone]
• Website http//www-staff.it.uts.edu.au/dcom
• Take care, and SMILE!!! )