Low Level
OSI Physical layer
https://en.wikipedia.org/wiki/Physical_layer
RFC
MAC bridge: http://profesores.elo.utfsm.cl/~agv/elo309/doc/802.1D-1998.pdf
Network Equipments
Switching Database Manager (SDM)
https://www.cisco.com/c/en/us/support/docs/switches/catalyst-3750-series-switches/44921-swdatabase-3750ss-44921.html
Ternary Content Addressable Memory (TCAM): rapid table lookups by ACL engine
If these resources are exhausted: Layer 2 Forwarding and Learning, a new learned address will be flooded to all ports within the ingress VLAN. Layer 3 Routing, any L3 unicast and multicast routes will be learned only in software and not programmed into the TCAM.
protocol data unit (PDU)
https://en.wikipedia.org/wiki/Protocol_data_unit
MTU
https://en.wikipedia.org/wiki/Maximum_transmission_unit Ethernet, the maximum frame size is 1518 bytes, 18 bytes of which are overhead (header and FCS), resulting in an MTU of 1500 byte.
| Media for IP transport | Maximum transmission unit (bytes) | Notes |
|---|---|---|
Internet IPv4 path MTU | At least 68,[5] max of 64KB[6] | Practical path MTUs are generally higher. Systems may use Path MTU Discovery[7] to find the actual path MTU. |
Internet IPv6 path MTU | At least 1280,[8] max of 64KB, but up to 4GB with optional jumbogram[9] | Practical path MTUs are generally higher. Systems must use Path MTU Discovery[10] to find the actual path MTU. |
Ethernet v2 | 1500[11] | Nearly all IP over Ethernet implementations use the Ethernet V2 frame format. |
Ethernet jumbo frames | 1501 – 9198 or more[14] | The limit varies by vendor. For correct interoperation, the whole Ethernet network must have the same MTU.[15] Jumbo frames are usually only seen in special-purpose networks. |
PPPoE over Ethernet v2 | 1492[16] | = Ethernet v2 MTU (1500) - PPPoE header (8) |
PPPoE over Ethernet jumbo frames | 1493 – 9190 or more[17] | = Ethernet Jumbo Frame MTU (1501 - 9198) - PPPoE header (8) |
WLAN (802.11) | 2304 | The maximum MSDU size is 2304 before encryption. WEP will add 8 bytes, WPA-TKIP 20 bytes, and WPA2-CCMP 16 bytes. |
MAC
12-34-56-78-9A-BC =》 000100{1}[0] 00110100 01010110 01111000 10011010 10111100 [0] individual addresses [1] group addresses
unicast
the frame is meant to reach only one receiving NIC. transmitted to all nodes within the collision domain.
In a modern wired setting the collision domain usually is the length of the Ethernet cable between two network cards.
In a wireless setting, the collision domain is as far as the radio transmitter can reach.
A switch will forward a unicast frame through all of its ports (except for the port that originated the frame), an action known as unicast flood, if the switch has no knowledge of which port leads to that MAC address.
multicast addressing
the frame will still be sent only once; however, NICs will choose to accept it based on criteria other than the matching of a MAC address: for example, based on a configurable list of accepted multicast MAC addresses. Group addresses, like individual addresses, can be universally administered or locally administered.
FF:FF:FF:FF:FF:FF. A broadcast frame is flooded and is forwarded to and accepted by all other nodes.
Applications
Extended Unique Identifier (EUI) -64 identifiers
IEEE 802
http://www.ieee802.org/
Ethernet II (DIX Ethernet) & 802.3 Frame
https://en.wikipedia.org/wiki/Ethernet_frame A version 1 Ethernet frame was never commercially deployed.
Preamble | 7 octets |
Start of frame delimiter | 1 octet |
MAC destination | 6 octets |
MAC source | 6 octets |
802.1Qtag (optional) | (4 octets) |
Ethertype(Ethernet II) or length (IEEE 802.3) | 2 octets |
Payload | 46‑1500 octets |
Frame check sequence(32‑bit CRC) | 4 octets |
Interpacket gap | 12 octets |
Layer 2 Ethernet frame: ← 64–1522 octets → Layer 1 Ethernet packet & IPG: ← 72–1530 octets → ← 12 octets →
The header = dst/src MAC + EtherType + optional IEEE 802.1Q tag
| Frame type | Ethertype or length | Payload start two bytes |
|---|---|---|
Ethernet II | ≥ 1536 | Any |
Novell raw IEEE 802.3 | ≤ 1500 | 0xFFFF |
IEEE 802.2 LLC | ≤ 1500 | Other |
IEEE 802.2 SNAP | ≤ 1500 | 0xAAAA |
EtherType can be used for two different purposes:
<=1500: the maximum length of the payload field of an Ethernet 802.3 frame is 1500 octets (0x05DC).>=1536: protocol encapsulated in the payload of the frame. used as EtherType, the length of the frame is determined by the location of the interpacket gap and valid frame check sequence (FCS).
most popular FCS algorithm is a cyclic redundancy check (CRC)
https://kb.juniper.net/InfoCenter/index?page=content&id=kb14737
a packet will occupy at least 12+8+64=84 / 92 / 96 bytes on the wire 1Gbps max PPS: 1,488,095 / 1,358,696 / 1,302,083
EtherType
MPLS
802.1Q & 802.1ad (Q-in-Q)
| 16 bits | 3 bits | 1 bit | 12 bits |
|---|---|---|---|
TPID | TCI | ||
PCP | DEI | VID |
Tag protocol identifier (TPID)： 0x8100/0x88A8 Tag control information (TCI)
Priority code point (PCP)： IEEE 802.1p class of service
Drop eligible indicator (DEI)/Canonical Format Indicator (CFI)： IEEE 802.1Q-2011 clause 6.9.3
VLAN identifier (VID)： up to 4,094 VLANs；0x000 no VLAN; 0x001 default; 0xFFF reserved.
Multiple VLAN Registration Protocol (MVRP), an application of the Multiple Registration Protocol, allowing bridges to negotiate the set of VLANs to be used over a specific link.
Cisco
VLAN Trunking Protocol (VTP) is a Cisco proprietary protocol that propagates the definition of Virtual Local Area Networks (VLAN) on the whole local area network.
Cisco Inter-Switch Link (ISL) is a Cisco Systems proprietary protocol that maintains VLAN information in Ethernet frames as traffic flows between switches and routers, or switches and switches. an alternative to the IEEE 802.1Q standard.
Dynamic Trunking Protocol (DTP) is a proprietary networking protocol developed by Cisco Systems for the purpose of negotiating trunking on a link between two VLAN-aware switches, and for negotiating the type of trunking encapsulation to be used.
IEEE P802.1p
| PCP value | Priority | Acronym | Traffic types |
|---|---|---|---|
1 | 0 (lowest) | BK | Background |
0 | 1 (default) | BE | Best effort |
2 | 2 | EE | Excellent effort |
3 | 3 | CA | Critical applications |
4 | 4 | VI | Video, < 100 ms latency and jitter |
5 | 5 | VO | Voice, < 10 ms latency and jitter |
6 | 6 | IC | Internetwork control |
7 | 7 (highest) | NC | Network control |
Bit Rate
https://en.wikipedia.org/wiki/Bit_rate
Net bit rate ≤ Gross bit rate (line rate)
IEEE 802.11a wireless network is the net bit rate of between 6 and 54 Mbit/s, while the gross bit rate is between 12 and 72 Mbit/s inclusive of error-correcting codes.
Ethernet 100Base-TX physical layer standard is 100 Mbit/s, while the gross bitrate is 125 Mbit/second.
Wireless
https://en.wikipedia.org/wiki/List_of_device_bit_rates
|Standard|Rate||Year| |---|---|---| |IEEE 802.11a|54 Mbit/s|6.75 MB/s|1999| |IEEE 802.11b|11 Mbit/s|1.375 MB/s|1999| |IEEE 802.11g|54 Mbit/s|6.75 MB/s|2003| |IEEE 802.16 (WiMAX)|70 Mbit/s|8.75 MB/s|2004| |IEEE 802.11n|600 Mbit/s|75 MB/s|2009| |IEEE 802.11ac (maximum theoretical speed)|6.8–6.93 Gbit/s|850–866.25 MB/s|2012| |IEEE 802.11ad (maximum theoretical speed)|7.14–7.2 Gbit/s|892.5–900 MB/s|2011|
FC
https://en.wikipedia.org/wiki/Fibre_Channel
|NAME|Line-rate (gigabaud)|Line coding|Nominal throughput/direction|Net throughput/direction| Availability| |---|---|---|---| |8GFC|8.5|8b10b|800|825.8|2005| |10GFC|10.51875|64b66b|1,200|1,239|2008| |16GFC|14.025|64b66b|1,600|1,652|2011| |32GFC "Gen 6"|28.05|64b66b|3,200|3,303|2016[6]| |128GFC "Gen 6"|28.05 ×4|64b66b|12,800|13,210|2016[6]|
Layers
Wireshark
https://wiki.wireshark.org/Ethernet#Frame_Check_Sequence_.28FCS.29_field
Design
https://www.cisco.com/c/en/us/products/collateral/switches/nexus-5000-series-switches/white_paper_c11-522337.html horizontal distribution area (HDA) access layer, or equipment distribution area (EDA)
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