NET 330 W2 Notes - Oliver-Mustoe/Oliver-Mustoe-Tech-Journal GitHub Wiki

NOTE: Information on this page is intended as notes and does contain text copy and pasted from readings/online sources. I do not claim to own this information, I have simply captured it for my studying needs.
Below are notes taken during/after class DATE:

Filename: D2 -- 9/5/22

Looking at networks from a enterprise perspective

Subnetting this week, real world

Case studies of subnetting

Scenario "Create network for new school, step 1 addressing, subnetting, hosts for faculty, for students, labs, data center, subnet mask I should use, appropriate ranges

Next week is enterprise DHCP

Possibly NAT and routing next

Subnetting in the real world

Be able to look at situation and be able to quickly identify what networks need

Patterns in subnets

4-5 subnet masks used in the wild

/24 - common

/30 - host is 2, point to point links

/29 - Couple of routers

/23 - same as 24

/22 - same as 24

/21 - same as 24

/26 - small labs

/27 - small labs

IP place values:

  • Highest value in an octet is 255

  • Common mistakes = not thinking about binary in third octet

When writing in binary, only 1's and 0's, place values

ARIN whois - find registry information

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

  • champlain:216.93.144.0/20

  • All Champlain IPs starts with the same 20 bits

  • We can use the remaining 12 bits (host ID) in any way we want

2 to the power of host bits = hosts (minus 2 (network id and broadcast))

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

  • Lost of broadcast packets congest the network

  • DHCP

  • ARP

  • Machines are slowed by trying to process them

  • Anyone can contact anyone else on the network

  • Firewalling problems

  • Isolation problems

  • Intrusion prevention not working properly

Subnetting:

  • Netid can't change, but what if we took some host ID bits to create a subnet ID?

/24 is default

/20 /21 = Usually wireless hosts

Broadcast layer 2

ARP for default gateway

Networks that are client heavy, /20 /21, /22, little interactive on VLAN, better for routers etc.

Going from place to place, client heavy places probably want same IP from place to place

In a datacenter, with servers talking to each other a lot, /24 /25 /26, lot of ARP traffic, security reasons

Different subnets are better for firewall rules

Subnetting rules

Start with the largest subnet first: Larger are always valid for smaller ones, but smaller are not always valid for larger ones.

Rules for IP addresses

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

All 0's and all 1s are allowed in subnet ID - NEW THING

Subnetting example

Subnets for campus:

Uni assigned 153.10.0.0/16

West campus - 500 users can use /21

East campus - 500 users can use /22

Central campus - 1000 users can use /23

Wireless campus - 1,600 users can use /23

Remember broadcast, remember that method I know calculates next network

Private and Reserved IP Ranges

  • Private Ranges not routable on Internet

  • 10.0.0.0/8

  • 172.16.0.0/12

  • 192.168.0.0/16

  • Reserved Ranges

  • 127.0.0.0/8 Loopback

  • 169.254.0.0/16 Link-Local Host Only

  • 244.0.0.0/4 Multicast

Multi-layer switching = like a switch, VLANS, and logic of router virtualized within it

Few dedicated routers, most of the time using distribution area switches

switches are layer 2, VLANS is making one switch and making it more

VLANS

  • 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

  • VLANs define broadcast domains in a Layer 2 network.

  • o Broadcast Domain: Set of all devices that will receive broadcast packets from 

  • any member of the set

  • o These are typically bounded by routers, who do not forward broadcasts.

    • VLANs are extremely flexible!

  • o They can split a single switch into several separate networks.

  • o They can merge machines on different switches into a single network.

Traffic cannot pass directly through vlans

Config VLANS:

Define 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 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

Once org has been subnetted, subnetting scheme has to be carried out on the physical infra

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.

Trunk ports will change the header

Cisco IOS:

Used on most Cisco switches and routers

CIOS configurations can be thought of as a big text file

When entering configuration commands, you are really just adding, removing, or editing a line in that file

Essentially two version of files

  • Startup config = Last version that was saved.

  • Running config = Version currently running in memory.

To save running-config

  • Command is: copy running-config startup-config

  • Copy run start - cisco cli

CIOS command modes:

User exec mode (basic): router>

Privileged mode (advanced, use command "enable"): router#

Global config (conf t, router as a whole): router(config)#

Enter the interface command (with a specific interface, such as interface ethernet 0) from 

global configuration mode: router (config-if)#

  • Access Ports (for end-devices)

  • o Config terminal

  • o Config interface port_name-number

  • o Switchport mode access

  • o Switchport access vlan vlan_id

    • Trunk ports (to connect switches) 

  • o Config terminal

  • o Config interface port_name-number

  • o Switchport mode trunk

  • o Switchport trunk allowed vlan vlan_range

Good cheat sheet: https://pbxbook.com/other/cidrcheat.html

"?" shows options:

After Class

Potential resources could use for hw:

https://www.accessagility.com/blog/benefits-of-subnetting#:~:text=Subnetting%20is%20the%20practice%20of,control%2C%20and%20improving%20network%20security.

https://www.networkcomputing.com/data-centers/5-subnetting-benefits

https://www.cbtnuggets.com/blog/cbt-nuggets/five-reasons-to-subnet

Good link for subnets:

https://www.techtarget.com/searchnetworking/definition/subnet 

"Each subnet allows its connected devices to communicate with each other, while routers are used to communicate between subnets. The size of a subnet depends on the connectivity requirements and the network technology employed. A point-to-point subnet allows two devices to connect, while a data center subnet might be designed to connect many more devices."

"Netmasks (or subnet masks) are a shorthand for referring to ranges of consecutive IP addresses in the Internet Protocol. They used for defining networking rules in e.g. routers and firewalls. Every entity (server or client) communicating on the internet will have a unique Internet Protocol (IP) address." -link