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CompTIA Network+ 1.1 Cisco CCNA 3.2 Cisco CCNA 1.13 Cisco CCST Networking 4.4
TechKnowSurge Catalog Interactives Frames and Packets, End to End
InteractiveNetworkFree

Frames and Packets, End to End

A PC asks a server two routers away for a page. Predict the addresses, the ARP and each router's work, hop by hop.

⚑ Complete this interactive to capture a CTF flag worth 5 points.

About this interactive

The lesson's walk-through, PC 192.168.0.10/24 to server 192.168.164.24: - **Local or remote:** the PC ANDs addresses with its mask. 192.168.164.24 is not on 192.168.0.0/24, so it goes to the default gateway, R1 at 192.168.0.1. - **ARP:** the PC asks for the gateway's MAC, not the server's, and caches the answer. The switch learns the PC's MAC and port from the request. - **The frame:** destination MAC is R1's; the packet inside is addressed to the server. - **Each router:** checks the frame is for it, strips it, looks up the destination, lowers the TTL, recomputes the header checksum, and builds a new frame for the next link (on a serial point-to-point link, that link's own framing). - **The last router** ARPs for the server itself, because the server's network is directly connected. The IP addresses stay the same end to end; the MAC addresses change at every hop. The video says a router does "a new frame check" after the TTL drops; it is the header checksum that is recomputed.

What you'll learn

Aligned to

CompTIA Network+
1.1 Explain concepts related to the Open Systems Interconnection (OSI) reference model.
Cisco CCNA
3.2 Determine how a router makes a forwarding decision by default
1.13 Describe switching concepts
Cisco CCST Networking
4.4 Explain basic routing concepts

Key terms

Address Resolution Protocol
ARP
A protocol used to map an IP address to a physical MAC address on a local network.
Default Gateway
The router that a device uses to send traffic to destinations outside its local network.
Time to Live
TTL
A value in a packet that limits its lifespan on a network, preventing it from circulating indefinitely.
Frame Check Sequence
FCS
A cyclic redundancy check value appended to the end of a data link frame that allows the receiver to detect transmission errors. The sending device calculates the FCS from the frame contents, and the receiving device recalculates it; a mismatch means the frame was corrupted and should be discarded.
Router
A network device that forwards data packets between networks based on IP addresses.

Topics

Layer 2 Layer 3 Arp Mac Address Ip Address Routing Interactive Predict

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