Network Design BasicsMM Clements

L2 Routing

IntroductionSubnetting ReviewLAN reviewApplying network numberingAdding more LANsAdding another routerNetwork numbering againRouting introduction

L2 Routing

SubnettingThe IPv4 address is 32 bits longBroken into dotted decimal for us humanse.g. 135.35.235.14We need to use binary to work out subnettingVital to understand decimal to binary conversion and vice versa

L2 Routing

Network and HostIP address has 2 parts network and hostThis cannot be seen from the IP address aloneWe need a way to show the boundaryThis is done with the subnet mask which is a 32 bit numberS/M uses 1s to show the network portion and 0s to show the host portion

L2 Routing

L2 Routing

Subnet MaskRouter performs logical AND with IP address and the subnet maskReveals the network this is all that is required when routing across internetworksHost part only required at destination LANCan be represented using slash notationSimply count the 1s in the subnet mask

L2 Routing

Use host 195.60.61.24 as an example

L2 Routing

LAN ReviewLAN is a group of hosts in a broadcast domainBroadcast crosses layer 2 devicesDoes not pass layer 3 e.g. routersRouter interface defines extent of a LANNeed Ethernet interface to create an Ethernet LANEthernet interface is normally given the lowest usable IP address in the IP range

L2 Routing

Defining IP RangeHow many host addresses required in LAN?Consider future expansion too at 10 25%Number of host IPs available = 2n -2 where n = number of host bitsE.g. 200 hosts requires 8 bits28 -2 = 254.. Plenty of addresses even including expansion

L2 Routing

Applying to router interfaceIn Packet Tracer 5.x, choose a router and make sure it has sufficient Ethernet interfacesIf not, add WIC or NMs that do have EthernetChoose lowest available IP address from the /24 range of addresses that you have chosenAllocate this to the Ethernet interfaceMake sure that the correct S/M is entered

L2 Routing

Adding more LANsMore LANs can be added to the same routerAdd sufficient Ethernet interfacesNumber the interfaces as previouslyPacket Tracer will give an error if addresses overlapPCs on LAN will need to be numberedAlso need to know default gateway IP (router)This could be manual or via DHCP

L2 Routing

LANs on same routerLANs on same router can communicateRouter can see both interfacesNo need for routing protocol hereUse ping to check communicationsshow ip route command displays routers routing tableAny network that appears in the routing table can be communicated with by router

L2 Routing

Adding another routerMake sure routers have at least one serial interface add these in Physical Device ViewConnect the serial interfaces between both routers and decide which interface will have the clockUsually interface closest to network coreThis is now the DCE interfaceDecide on a clock rate 64000 is common but slowApply the clockrate to the DCE interface onlyNon-clocked interface is known as DTE

L2 Routing

Numbering serial interfacesSerial link will only ever have 2 hostsIt would be a waste to add a /24 address rangeSolution is to use /30 address range/30 subnet has only 2 host addressesApply these to the serial interfacesMake sure the interface is turned onshow ip interface brief command will give a summary of the interface states

L2 Routing

TroubleshootingScreenshot above shows that Serial 0/1 interface is not functioning.It has IP address but its Status is administratively down and Protocol is downCheck that the interface is actually turned onCLI uses no shutdown command to activate an interface

L2 Routing

Add LAN to second routerApply numbering to new Ethernet LAN interface on the 2nd routerAdd some host PCs they need IP addressingManual configuration or DHCP is OKLAN on first router cannot connect to second routers LANExamine routing table to discover why

L2 Routing

Routing tableRouter can only see connected networks C = connected, look at Codes

L2 Routing

Router communicationsRouter will need to know how to get to the other LANsThis information is learned by a routing protocolPacket tracer implements RIP, OSPF and EIGRPImplement a routing protocol on all routers in the networkCompare the routing table nowHow did it learn about the other LANs?Check the codes to see which routing protocol was used

L2 Routing

Routing Table

L2 Routing

L2 Routing

Routing ProtocolsRouting can be either static or dynamicRouting protocols allow for dynamic routingChanges to network are automatically catered for2 types of dynamic routing protocols existLink State and Distance VectorMore next week

L2 Routing

SummaryAddress Ethernet interfaces on routerLowest IP address on LAN for interfaceAdd WICs or NMs as neededUse /30 between routers on serial interfacesChoose DCE and DTE on serial linksA routing protocol is needed to send data between 2 routersPractical work reinforces these concepts

L2 Routing