Networking
The structure of this overview follows the OSI layers.
Physical
10Base-T
802.3i-1990 - IEEE Standard for Local and Metropolitan Area Networks.
100Base-T
1000Base-T
Single Pair Ethernet
- 802.3cg (10Base-T1)
- 802.3bw (100Base-T1)
- 802.3bp (1000Base-T1)
- 802.3ch (Multi-Gig Automotive Ethernet)
Data Link
Ethernet Frame
Min length: 64 bytes Max length: MTU (defaults to 1518 - 1522(Vlan))
In case the ethernet header + the ethernet payload has less than 64 bytes, the frame is padded. This is typically done by the ethernet driver / network card. Packet filters (tcpdump) see the leaving packets before they go threw the HW, and therefore can not see the padding. Wireshark also cuts off the FCS.
IEEE 802.3 Ethernet Header
| 7 bytes | 1 byte | 6 bytes | 6 bytes | 2 bytes | 2 bytes | 46-1500 bytes | 4 bytes |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preamble | Start Frame | Destination | Source | Ether type | Ether type | Payload | FCS |
| | Delimiter | Address | Address | Size | Size | | CRC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Network
IPv4
Address: 192.168.000.1
Subnet Mask: 255.255.255.0
Network: 192.168.0.0/24
Address:
- dotted decimal:
192.168.0.1 - binary:
11000000.10101000.00000000.00000001 - network byte order: big endian
1 byte = 8 bit 1 byte:
most significant bit least significant bit
| |
| |
1 |1 |1 |1 |1 |1 |1 |1
----|----|----|----|----|----|----|----
128 |64 |32 |16 |8 |4 |2 |1
Subnet Mask
Internet /0 00000000.00000000.00000000.00000000 0.0.0.0 Class A /1 10000000.00000000.00000000.00000000 128.0.0.0 ... Class A /8 11111111.00000000.00000000.00000000 255.0.0.0 Class B /9 11111111.10000000.00000000.00000000 255.128.0.0 ... Class B /16 11111111.11111111.00000000.00000000 255.255.0.0 Class C /17 11111111.11111111.10000000.00000000 255.255.128.0 ... Class C /24 11111111.11111111.11111111.00000000 255.255.255.0 Hosts /25 11111111.11111111.11111111.10000000 255.255.255.128 Hosts /26 11111111.11111111.11111111.11000000 255.255.255.192 Hosts /27 11111111.11111111.11111111.11100000 255.255.255.224 Hosts /28 11111111.11111111.11111111.11110000 255.255.255.240 Hosts /29 11111111.11111111.11111111.11111000 255.255.255.248 Hosts /30 11111111.11111111.11111111.11111100 255.255.255.252 Hosts /31 11111111.11111111.11111111.11111110 255.255.255.254 Hosts /32 11111111.11111111.11111111.11111111 255.255.255.255
/24 -> 255.255.255.0 -> 8 host bits -> 254 Host Addresses /16 -> 255.255.0.0 -> 16 host bits -> 65.534 Host Addresses
Classless Interdomain Routing (CIDR) /20 -> 255.255.v
Network