Name the IPv4 Header Field

About this interactive

The lesson's IPv4 header, top to bottom: - **Version** (4 bits): 0100 for IPv4. **IHL**: the header's length in 32-bit lines, usually 5 (20 bytes); more than 5 means **Options** are present. - **DSCP** (6 bits): marks how routers should treat the packet, such as voice first; it used to be Type of Service. **ECN** (2 bits): signals congestion. The video also says DSCP tells what the payload is; that is the Protocol field's job. - **Total Length** (16 bits): header plus payload, at most 65,535 bytes. - **Identification**, **Flags** and **Fragment Offset**: which packet a fragment belongs to, whether more follow, and where its data fits. - **TTL**: lowered by one at each router; the packet is dropped at zero, which stops routing loops. - **Protocol**: what the payload carries, such as TCP or UDP. **Header Checksum**: checks the header, recomputed at every router because the TTL changed. - **Source Address** and **Destination Address**: 32 bits each.

What you'll learn

Name the IPv4 header field that does a job: version, IHL, DSCP, ECN, total length, TTL, protocol, header checksum, source and destination address, and options
Name the fragmentation fields (identification, flags, fragment offset) and work the header's sizes and counts: IHL to bytes, payload from total length, TTL after a number of routers

Aligned to

CompTIA Network+

1.4 Explain common networking ports, protocols, services, and traffic types

Cisco CyberOps Associate

4.8 Interpret the fields in protocol headers as related to intrusion analysis

Key terms

IP Packet Header: The portion of an IP packet that contains control information, including the source and destination IP addresses, prepended to the payload.
Internet Header Length: A 4-bit field in the IPv4 header that specifies the total length of the IP header in 32-bit words, indicating where the payload begins.
Time to Live: A value in a packet that limits its lifespan on a network, preventing it from circulating indefinitely.
Fragment Offset: A 13-bit field in the IPv4 header that indicates the position of a fragment relative to the original unfragmented packet, enabling correct reassembly.
Differentiated Services Code Point: A 6-bit value in the IP header's Type of Service field used to mark packets for differentiated forwarding treatment in a DiffServ network. Routers read the DSCP marking to apply the appropriate queuing, scheduling, and drop policy.
Explicit Congestion Notification: A 2-bit field in the IPv4 header that allows network devices to signal congestion to endpoints without dropping packets.
Checksum: A value calculated from packet header data and used to detect errors; recalculated by a router after modifying the IP header fields such as TTL.

Topics

Ipv4 Ip Header Ttl Ihl Fragmentation Interactive Fill In

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