Introduction to Networking Ahmad Omary Architect Mellanox BGU
Introduction to Networking Ahmad Omary | Architect, Mellanox BGU High-performance communication, 2017
Agenda § Network definition § Networking models (protocol stacks) § Topologies § Network devices § ECMP vs. Adaptive routing in Fat Tree © 2016 Mellanox Technologies 2
What is a “Network”? § A collection of nodes that are connected in various ways in order to communicate and share resources. • Nodes: • • Servers – web, file, compute Computers Phones Printers • Connected: • • Cable media Wireless media • Ways: • Topology • Communicate using: • protocol © 2016 Mellanox Technologies 3
OSI 7 -layer model © 2016 Mellanox Technologies 4
Traffic flow © 2016 Mellanox Technologies 5
TCP/IP model © 2016 Mellanox Technologies 6
Topologies § A topology is a way of “laying out” the network. Topologies can be either physical or logical. § Physical topologies describe how the cables are run. § Logical topologies describe how the network messages travel § Basic topologies: • • Bus Start Ring Mesh © 2016 Mellanox Technologies 7
Topologies – Bus § The simplest physical topology. § A single cable that runs to every workstation. § Each computer shares the same data and address path. § A signal from the source travels in both directions to all machines connected on the bus cable until it finds the intended recipient. § If the machine address does not match the intended address for the data, the machine ignores the data. § Alternatively, if the data matches the machine address, the data is accepted. © 2016 Mellanox Technologies 8
Bus - Advantages and Disadvantages § Advantages: • Inexpensive - Least amount of cabling § Disadvantages: • • Covers the shortest amount of distance. Performance. Single point of failure. Security © 2016 Mellanox Technologies 9
Topologies – Star § Each host is connected to a central device called a hub with a point-to-point connection. § All traffic that traverses the network passes through the central hub © 2016 Mellanox Technologies 10
Star - Advantages and Disadvantages § Advantages: • Simple to manage and add new host. • Host fail doesn’t cause network fail § Disadvantages: • Expensive. • The hub represent a single point of failure. • Performance – hub is a bottleneck. © 2016 Mellanox Technologies 11
Topologies – Ring § A ring topology is a bus topology in a closed loop. § Data travels around the ring in one direction. § When one node sends data to another, the data passes through each intermediate node on the ring until it reaches its destination. § The intermediate nodes repeat (re transmit) the data to keep the signal strong. § Every node is a peer; there is no hierarchical relationship of clients and servers. © 2016 Mellanox Technologies 12
Ring - Advantages and Disadvantages § Advantages: • Better performance than bus topology (not Star). • There is no need of network server to control the connectivity between workstations. § Disadvantages: • Difficult to add new host • If one node is unable to re transmit data, it severs communication between the nodes before and after it in the bus. • Aggregate network bandwidth is bottlenecked by the weakest link between two nodes. © 2016 Mellanox Technologies 13
Topologies – Mesh § The mesh topology is the simplest logical topology in terms of data flow, but it is the most complex in terms of physical design. § In this physical topology, each device is connected to every other device. • Simplest logical topology in terms of data flow. • Most complex in terms of physical design. § For n hosts, there will be (n × (n– 1)) ÷ 2 cables in the network. © 2016 Mellanox Technologies 14
Mesh - Advantages and Disadvantages § Advantages: • High fault tolerance. § Disadvantages: • Very expensive © 2016 Mellanox Technologies 15
Datacenter/Cloud Networks Today’s datacenters networks: § Large clusters. • Include 1000 s of physical servers. • Each with 100 s of VMs. § Enable communication between each pair of VMs in the network. § Which of there topologies can be used ? • • Bus Star Ring Mesh © 2016 Mellanox Technologies 16
Fat Tree topology § How can I connect hundreds/thousands of hosts? § Can these topologies be use for data center or Cloud? © 2016 Mellanox Technologies 17
Fat Tree § 3 - Level Fat-tree topology. S © 2016 Mellanox Technologies D 18
Network devices § Network Interface Card (NIC) § Repeater § Hub § Routers § Switch © 2016 Mellanox Technologies 19
Network Interface Card (NIC) § NIC provides the physical interface between host and network. • It prepares data, sends data, and controls the flow of data. • It receives data from network, and translate into bytes for the CPU to understand. • Manages flow control with next network device (or other devices in more complicated mechanisms). § Performance is the most important factors of a NIC: • Maximize Bandwidth • Minimize the amount of time needed to transfer data packets across the network (latency). • Better CPU utilization when sending and receiving data - DMA – Direct memory access - RDMA - CPU offloads § § § Packet checks (checksum) Steering Packet modification Encryption/ Decryption Firewall © 2016 Mellanox Technologies 20
Repeaters § They allow a cabling system to extend beyond its maximum allowed length by amplifying the network voltages so they travel farther. § Repeaters are nothing more than amplifiers and, as such, are very inexpensive. § Repeaters can only be used to regenerate signals between similar network segments. § The main disadvantage to repeaters is that they just amplify signals. These signals not only include the network signals, but any noise on the wire as well. § Eventually, if you use enough repeaters, you could possibly drown out the signal with the amplified noise. For this reason, repeaters are used only as a temporary fix. © 2016 Mellanox Technologies 21
Hubs § Hubs are devices used to link several computers together. § They repeat any signal that comes in on one port and copy it to the other ports (a process that is also called broadcasting). § There are two types of hubs: active and passive. § Passive hubs simply connect all ports together electrically and are usually not powered. § Active hubs use electronics to amplify and clean up the signal before it is broadcast to the other ports. © 2016 Mellanox Technologies 22
Switch § A network switch is a computer networking device that connects network segments. § Low-end network switches appear nearly identical to network hubs, but a switch contains more "intelligence" (and a slightly higher price tag) than a network hub. § Network switches are capable of inspecting data packets as they are received, determining the source and destination device of that packet, and forwarding it appropriately. § By delivering each message only to the connected device it was intended for, a network switch conserves network bandwidth and offers generally better performance than a hub. § A vital difference between a hub and a switch is that all the nodes connected to a hub share the bandwidth among themselves, while a device connected to a switch port has the full bandwidth all to itself. § For example, if 10 nodes are communicating using a hub on a 10 -Gbps network, then each node may only get a portion of the 10 Gbps if other nodes on the hub want to communicate as well. . § But with a switch, each node could possibly communicate at the full 10 Gbps. © 2016 Mellanox Technologies 23
Switch forwarding decision § Each switch has a Forwarding Data Base(FDB) • Classical solution in today’s vendor switches. • Allocates the output port of a flow • Static configuration: - By a Centralized controller (SDN). • Dynamic configuration: - Remember output port of a flow after the first transmission. - Ageing mechanisms to delete old flows. © 2016 Mellanox Technologies 24
Hubs vs. Switches § Hubs are shared media devices. Everyone sees everyone’s packets, you’re only supposed to pay attention to those specifically directed to you, or to broadcasts. • • • Not too secure Cheap. Most wireless still qualifies as a “hub, ” while actual wired ethernet hubs are becoming hard to find. § Switches aren’t shared, most of the time. Known traffic forwarded to the specific output port, and only unknown packets and broadcasts still go to all ports. § generally more secure. § Switches are now much more common than hubs. © 2016 Mellanox Technologies 25
Routers § Routers are highly intelligent devices that connect multiple LANs. § Analyze every packet and determine the best path for routing the data. § Forwarding decision depend on routing tables (Layer 3) § Expensive. © 2016 Mellanox Technologies 26
Back to Fat Tree - ECMP § Equal cost multi path routing S © 2016 Mellanox Technologies D 27
Back to Fat Tree – Adaptive routing § Route to the least congested output port S © 2016 Mellanox Technologies D 28
Thank You
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