Introduction to Networking (Routing & Switching) Nir Ingbar

Agenda OSI 7 Layers model Layer 1 & 2 Frame forwarding & filtering VLAN, dot1Q Trunking IP Routing

OSI 7 Layers model (1977 by ISO)

OSI Model Layer’s definitions Each OSI layer performs unique and specific task A layer only has a knowledge of its adjacent layers A layer uses the services of a layer below A layer performs functions and provides service to the layer above A layer service is independent of its implementation Application Presentation Session Transport Network Data Link Physical

OSI Model Layers Physical: Electrically encodes and physically transfers messages between nodes Data Link: Provides reliable transit of data across a physical link, handling physical addressing, link discipline, error detection, ordered delivery of frames and flow control Network: Provides connectivity and path selection between two end systems that may be located on geographically diverse sub-networks Transport: End- to- end control & information exchange with a level of reliability required for the applications

OSI Model Layers (cont.) Session: Manages the connection between cooperating applications Presentation: Transforms data to and from negotiated standardized formats Application: Provides the window between the application process and OSI

* FCS (Frame Check Sequence) Data encapsulation Data Application Application Data Presentation Presentation SH Data Unit Session Session TH Data Unit Transport Transport NH Data Unit Network Network DLH Data Unit FCS Data Link Data Link Bits Physical Physical * FCS (Frame Check Sequence)

Internetworking Devices Application Application Presentation Presentation Session Session Transport Transport Network Router Network Data Link Switch/Bridge Data Link Physical Hub/Repeater Physical

Ethernet, Token Ring, FDDI, Protocol Suite Application Telnet FTP SMTP TFTP BOOTP SNMP Presentation Session Transport TCP UDP Network IP ICMP ARP Data Link Ethernet, Token Ring, FDDI, WAN synchronous Physical

Layer 1 & 2

Device Types Hub - multi port repeater, provide connectivity, allowing attached devices a path between which they can communicate, works on layer one Switch – connecting hosts Bridge – connecting networks, can’t identify different logical networks

Bridge vs. Switch Bridge usually have two interfaces and can connect to physical networks Switches usually have more than that The main difference between a switch and bridge is the number of networks each can connect Switches are often aimed to connect workstations in a single junction Both are used inside LAN Both operates on layers one and two

Collision Domain one of the logical network segments in which the data packets can collide to each other Collision domains are often referred as ‘Ethernet segments'. defined as a single CSMA/CD network segment in which there will be a collision if two computers attached to the system both transmit at the same time A collision occurs when two or more network devices are trying to transmit packets at the exact same time

Collision domain - example

Collision domain - example

Type Of Transmission Unicast - unicast transmission is the sending of information packets to a single destination Broadcast - broadcasting refers to transmitting a packet that will be received (conceptually) by every device on the broadcast domain Multicast - multicast is a network addressing method for the delivery of information to a group of destinations simultaneously Anycast – like multicast but only one address of a set of addresses is chosen at any given time to receive information from any given sender

MAC Address 48 bits (6 octets) address space representing an unique identifier to most network adapters or network interface cards (NIC) The first three octets identify the organization that issued the identifier and are known as the Organizationally Unique Identifier (OUI) 00-16-D3-C4-55-6A

Broadcast Domain represents the systems to which a given broadcast will travel broadcasts do not pass routers by default If one station will broadcast, all the stations in this domain will get the message If a station wants to send a message out of the LAN, it will have to know it’s Default Gateway

Broadcast domain – simple example

Collision domain- problem

One switch can be a Single Point Of Failure Adding an additional Switch can create broadcast storm.

Solution: STP – Spanning tree Protocol On running this algorithm the LAN is reduced to an acyclic tree The main idea of the Spanning Tree is for the bridges to select the ports over which they will forward frames

Spanning Tree Protocol Spanning tree is designed to prevent loops in bridged/switched Ethernet network based on the root bridge concept, which is selected via programmable parameters L4 L3 Actual Network L2 L5 L1 B1 B4 B3 B5 B2 With Spanning Tree B5 B3 L2 L1 L3 L4 L5 B1 B2 B4 X

Frame forwarding & filtering

Frame forwarding & filtering The initial MAC address is empty

Frame forwarding & filtering (cont.) Station A sends a frame to station C The switch caches the MAC address of station A to port E0 by learning the source address of data frames The frame from station A to station C is flooded out to all ports except port E0

Frame forwarding & filtering (cont.) Station D sends a frame to station C The switch caches the MAC address of station D to port E3 by learning the source address of data frames The frame from station D to station C is flooded out to all ports except port E3

Frame forwarding & filtering (cont.) Station A sends a frame to station C The destination is known; the frame is not flooded

VLAN, dot1Q Trunking

VLAN, dot1Q Trunking 802.1Q Frame FCS (Frame Check Sequence) is recalculated

Importance of native VLANs VLAN 1 untagged traffic (native VLAN) An 802.1Q trunk and its associated trunk ports have a native VLAN value. 802.1Q does not tag frames for native VLAN. Therefore, ordinary stations will be able to read the native untagged frames, but will not be able to read any other frame because the frames are tagged

IP

Relies on a transport protocol to guaranty delivery Internet Protocol - IP Network Layer Provides network layer services to TCP/IP protocol suite Responsible for forwarding packets through network based on IP addresses “Best effort” delivery Connectionless Unacknowledged Relies on a transport protocol to guaranty delivery

IPv4 Addressing Address format: XXX.XXX.XXX.XXX (0≤XXX≤255) Addresses are 32 bits long (4,294,967,296 IP addresses) Internet Assigned Numbers Authority (IANA) assigns IP addresses for the Internet Divided into five classes three of which are available to end-user networks Consists Network and Host identification fields

Available IP Addresses Class Assigned Network/ /Host ID Range of Network IDs Max. Hosts Per Network A /8 NET.X.X.X 1 –126 16,777,214 B /16 NET.NET.X.X 128.1 – 191.254 65,534 C /24 NET.NET.NET.X 192.0.1 – 223.255.254 254 Class D is reserved for multicast groups Class E is reserved for future use

Private Networks RFC 1918 addresses RFC 2026—Link Local Addresses Not routed by Internet routers (filtered by Edge Routers) RFC 2026—Link Local Addresses 169.254.0.1–169.254.255.255 Auto-assigned IP address to local host if DHCP server cannot be contacted Not routed by any router Class Assigned Network/ /Host ID Range of Network IDs A NET.X.X.X 10.0.0.0 - 10.255.255.255 B NET.NET.X.X 172.16.0.0 - 172.31.255.255 C NET.NET.NET.X 192.168.0.0 - 192.168.255.255

Other Reserved Addresses 127.0.0.1–127.255.255.255 Reserved for testing and loopback routines for IP Applications ping 127.0.0.1—verifies the local host has properly loaded the IP protocol 224.0.0.1–224.0.0.255—Class D multicast (IANA) Reserved for well known services and network topology mechanisms

Subnetting IP/VLSM/Classless Allows to divide a single IP network into smaller divisions – Subnets Done by borrowing bits from the host portion of the address Subnet bits are defined by the Subnet Mask IP Address 134.125.172.17 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Subnet Mask 255.255.240.0 Or /20 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Subnet Host

Summary Host-to-Host Packet Delivery (1 of 22)

Host-to-Host Packet Delivery (2 of 22)

Host-to-Host Packet Delivery (3 of 22)

Host-to-Host Packet Delivery (4 of 22)

Host-to-Host Packet Delivery (5 of 22)

Host-to-Host Packet Delivery (6 of 22)

Host-to-Host Packet Delivery (7 of 22)

Host-to-Host Packet Delivery (8 of 22)

Host-to-Host Packet Delivery (9 of 22)

Host-to-Host Packet Delivery (10 of 22)

Host-to-Host Packet Delivery (11 of 22)

Host-to-Host Packet Delivery (12 of 22)

Host-to-Host Packet Delivery (13 of 22)

Host-to-Host Packet Delivery (14 of 22)

Host-to-Host Packet Delivery (15 of 22)

Host-to-Host Packet Delivery (16 of 22)

Host-to-Host Packet Delivery (17 of 22)

Host-to-Host Packet Delivery (18 of 22)

Host-to-Host Packet Delivery (19 of 22)

Host-to-Host Packet Delivery (20 of 22)

Host-to-Host Packet Delivery (21 of 22)

Host-to-Host Packet Delivery (22 of 22)

Default Gateway

Routing

Routers Routers have the following components: – CPU – Motherboard – RAM – ROM Routers have network adapters to which IP addresses are assigned. Routers may have the following two kinds of ports: – Console: For the attachment of a terminal used for management – Network: Different LAN or WAN media ports Routers forward packets based upon a routing table

Router Functions Lets other routers know about changes Determines where to forward packets Translate between different layer2 protocols/interfaces RouterX# show ip route D 192.168.1.0/24 [90/25789217] via 10.1.1.1 R 192.168.2.0/24 [120/4] via 10.1.1.2 O 192.168.3.0/24 [110/229840] via 10.1.1.3

Routing Types Static/Dynamic IGP (Interior Gateway Protocol) – RIP, ISIS, OSPF, (E)IGRP EGP (Exterior Gateway Protocol) - BGP

Path Determination

Routing Tables

Routing Table Entries Directly connected: Router attaches to this network Static routing: Entered manually by a system administrator Dynamic routing: Learned by exchange of routing information Default route (optional): Statically or dynamically learned; used when no explicit route to network is known

Routing Metrics

Distance Vector Routing Protocols Passes periodic copies of routing table to neighbor routes and accumulates distance vectors

Link-State Routing Protocols All routers calculate “shortest paths” using Djikstra algorithm After initial flood, passes small event-triggered link-state updates to all other routers

Routing Protocols Distance Vector – RIP, IGRP Link State – OSPF, ISIS Balanced hybrid - EIGRP

Administrative Distance Route Source Default Distance Connected Static 1 eBGP 20 EIGRP 90 IGRP 100 OSPF 110 ISIS 115 RIP 120 iBGP 200 Unknown* 255 * If the administrative distance is 255, the router does not believe the source of that route and does not install the route in the routing table