Notes2:1SubnettingVlans - echadbourne/NET-330 GitHub Wiki

IP Place Values

The highest value in an octet is 255

Looking at the place values, all 1's in the 8 bits is

  • 128+64+32+16+8+4+2+1

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Subnetting

Organizations are "assigned" a network address to use on the internet

  • Champlain College: 216.93.144.0/20
  • All Champlain IPs start with the same 20 bits
  • We can use the remaining 12 bits (host ID) in any way we want

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(2 to the 12th)

But a /20 network can support 4094 hosts - do we want them all on the same network

  • Lots of broadcast packets congest the network
  • Machines are slowed by trying to process them
  • Anyone can contact anyone else on the network

Our network ID can't change but what if we took some host ID bits to create a subnet ID

  • These bits are then "added" to the network ID (i.e. the subnet mask now covers them)
  • For example, if we used 4 bits for the subnet ID...

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Subnet Table

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Creating a Subnet

Always start with the largest subnet first: larger subnet boundaries are always valid for smaller ones, but smaller boundaries are not always valid for larger ones

For example, consider arranging /22 and /24 subnets for 129.170.8.0/16

If we start with /22:

  • 129.170.8.0/22 (ranges from 129.170.8.1 to 129.170.11.254)
  • 129.170.12.0/24 (ranges from 129.170.12.1 to 129.170.12.254)

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If we start with /24:

  • 129.170.8.0/24 (ranges from 129.170.8.1 to 129.170.8.254)
  • 129.170.9.0/22 (ranges from 129.170.9.1 to 129.170.12.254)

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IP Rules

All 0's in the host ID refers to the network itself - cannot be assigned to a host

All 1's in the host ID is the broadcast - cannot be assigned to a host

So if we have n bits in our host ID, we can assign 2(to the n) - 2 IP addresses to hosts on our network

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Private and Reserved Ranges

Private ranges not routable on the internet

  • 10.0.0.0/8
  • 172.16.0.0/12
  • 192.168.0.0/16

Reserved Ranges

  • 127.0.0.0/8
  • 169.254.0.0/16
  • 224.0.0.0/4

VLANs

A Virtual LAN is a group of devices on one or more physical LANs that are configured to communicate as if they were on the same LAN

Define broadcast domains in a layer 2 network

  • Broadcast Domain: set of all devices that will receive broadcast packets from any member of the set
  • These are typically bounded by routers, who do not forward broadcasts

VLANs are extremely flexible

  • They can split a single switch into several separate networks
  • They can merge machines on different switches into a single network

Traffic cannot pass directly between different VLANs

To send packets between VLANs, a router or layer 3 switch is required

VLANs are often associated with specific IP subnets

Configuring VLANs

Define the necessary VLANs on each switch

  • Choose a unique VLAN ID for each VLAN
  • ID must be consistent across all switches involved

Configure the ports on each switch - 2 possible options

  • Access Ports: Can only be assigned to/carry traffic from a single VLAN - Used to connect end devices to a switch
  • Trunk Ports: Carry traffic from multiple VLANs - used to connect switches - will "tag" packets with the proper VLAN ID

VLANs are an implementation of VLSM

  • Once you've subnetted your oganization, the subnetting scheme has to be carried out on the physical infrastructure
  • When subnets occupy the same physical space, we can use VLANs to keep devices on separate networks, even though they are next to each other physically