Protocol Configuration

Transcription

1 Configuration

2 Protocol Configuration Many items must be set before protocols can be use IP aress of each network interface Aress mask for each network Initial values in the forwaring table Process is known as protocol configuration Usually occurs when operating system boots Two basic approaches Manual Automatic Computer Networks an Internets -- Moule 5 99 Spring, 2014 Copyright 2014 All rights reserve

3 Manual Configuration Use for IP routers or host that has a permanent IP aress Manager Enters configuration once Specifies that the configuration be save in non-volatile storage Interfaces inclue Comman Line Interface (CLI) an web OS Fetches values from non-volatile storage whenever the evice boots Computer Networks an Internets -- Moule Spring, 2014 Copyright 2014 All rights reserve

4 Automatic Configuration Use primarily for hosts Initially create for iskless workstations Basic iea Use network to obtain configuration information Configure protocol software, an then start to run applications A seeming paraox Automatic configuration requires a computer to be able to use a network before the computer s protocol parameters have been configure Computer Networks an Internets -- Moule Spring, 2014 Copyright 2014 All rights reserve

5 Ways To Solve The Paraox Use layer 2 protocols to obtain layer 3 parameters, then use layer 3 to obtain higher layers Historic approach Relie on Ethernet broacast One computer on a network respone to requests Use layer 3 to obtain all parameters Current approach Relies on IP broacast (IPv4) or multicast (IPv6) Means routers can forwar requests to a remote server Computer Networks an Internets -- Moule Spring, 2014 Copyright 2014 All rights reserve

6 Dynamic Host Configuration Protocol (DHCP) The stanar protocol for automatic configuration Popular in private enterprises as well as with service proviers Host broacasts/multicasts a request an receives a reply Single message exchange allows a host to obtain An IP aress an aress mask to use The IP aress of a efault router The aress of a DNS server A DNS name The location of an image to boot (optional) Computer Networks an Internets -- Moule Spring, 2014 Copyright 2014 All rights reserve

7 DHCP Message Format Same message format use for requests an responses OP HTYPE HLEN HOPS TRANSACTION IDENTIFIER SECONDS ELAPSED FLAGS CLIENT IP ADDRESS YOUR IP ADDRESS SERVER IP ADDRESS ROUTER IP ADDRESS CLIENT HARDWARE ADDRESS (16 OCTETS) SERVER HOST NAME (64 OCTETS) BOOT FILE NAME (128 OCTETS) OPTIONS (VARIABLE) Computer Networks an Internets -- Moule Spring, 2014 Copyright 2014 All rights reserve

8 DHCP Protocol Significant features of the protocol Recovers from loss or uplication Avois synchronize flooing of requests after a powerfailure an restart Host iscovers DHCP server once an caches server aress for future interaction Derive from BOOTstrap Protocol (BOOTP), but as ynamic aress assignment Computer Networks an Internets -- Moule Spring, 2014 Copyright 2014 All rights reserve

9 Aress Lease Paraigm DHCP server Owns a set of IP aresses Chooses an aress from the set when a request arrives Issues a lease for the aress for specifie time, T Client Obtains an aress an starts a timer for T time units Uses the aress to communicate When the timer expires, requests the server renew the lease Either receives a renewal an restarts timer or stops using the aress Computer Networks an Internets -- Moule Spring, 2014 Copyright 2014 All rights reserve

10 Thought Problem Consier how aresses are assigne An ISP using DHCP can choose which IP aress to assign to a customer at a given time There are two approaches The ISP can remember which aress was previously assigne to each customer an use the same aress The ISP can assign aresses at ranom, meaning the customer will not retain the same aress Many ISPs try to change the aress frequently Why? Computer Networks an Internets -- Moule Spring, 2014 Copyright 2014 All rights reserve

11 IPv6 Configuration DHCPv6 has been efine, but IPv6 prefers a new proceure known as IPv6 autoconfiguration General iea: host can generate an aress without using a server Motivation: allow two hosts to communicate without further infrastructure Computer Networks an Internets -- Moule Spring, 2014 Copyright 2014 All rights reserve

12 Steps In IPv6 Autoconfiguration Obtain a network prefix Convention is to use a /64 prefix Globally-vali prefix can be obtaine from a router Local-scope prefix create if no router available Generate a unique suffix Verify that no one else on the network is using the resulting aress Computer Networks an Internets -- Moule Spring, 2014 Copyright 2014 All rights reserve

13 IPv6 Autoconfiguration in Practice Nee a unique host suffix For /64 network, a 64-bit host suffix is neee Recommene approach Start with MAC aress (globally unique, but only 48 bits) Create a 64-bit value IEEE stanar EUI-64 specifies how 48 bits of an IEEE MAC aress are place in a 64-bit host suffix Computer Networks an Internets -- Moule Spring, 2014 Copyright 2014 All rights reserve