---
description: 'Week 1: 8/29/22'
---

# Week 1: Subnet Refresher

* Dartmouth had hundreds of subnets just in the datacenter
* 2^32 IPv4 addresses | 32 bits

| Letter                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | Packet                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
| ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| <ol><li>Look up recipient address</li><li><p></p><ol><li>Phone Book? Other Directory?</li><li>Get zip code and street address</li></ol></li><li>Put in addressed envelope</li><li><p></p><ol><li>Write recipient and return address on envelope</li></ol></li><li>Put letter in mailbox</li><li>Mail carrier picks letter up</li><li><p></p><ol><li>Take letter to local post office</li></ol></li><li>Post Office sorts and sends to next PO facility</li><li><p></p><ol><li>Uses zip code</li></ol></li><li>How does PO know where to send next?</li><li><p></p><ol><li>Postal Service has “routing lists”</li></ol></li><li>Ends up at local PO recipient</li><li>Mail Carrier delivers to recipient</li><li><p></p><ol><li>Uses street address</li></ol></li></ol> | <ol><li>Look up recipient address</li><li><p></p><ol><li>Domain Name System (DNS)</li><li>Convert Hostname to IP address</li></ol></li><li>Add “Headers” to data (encapsulate)</li><li>Send packet to network interface controller (NIC)</li><li>Transmits onto network</li><li><p></p><ol><li>Sent to local router (AKA default gateway)</li></ol></li><li>Router sends packet to next router</li><li><p></p><ol><li>Uses network part of the IP Address</li></ol></li><li>How does the router know where to send next?</li><li><p></p><ol><li>“Routing table” of IP networks</li></ol></li><li>Ends up at local router of recipient</li><li>Router and switches send to recipient</li><li><p></p><ol><li>Uses Host part and IP address and Mac address`</li></ol></li></ol> |

* [grandma@aol.com](mailto:grandma@aol.com)
* &#x20;  ^Mailbox  ^ Mail server -> translates to ip address

TODO:

* Download Packet Tracer 8.1.1
