BOOTP Limitations. Dynamic IP Address Assignment. DHCP IP address assignment. Dynamic Host Configuration Protocol (DHCP)

Transcription

1 slide 1 Dynamic IP Address Assignment BOOTP Limitations slide 2 BOOTP provides a configuration setting for a client IP address, operating system, subnet mask, dns server, gateway address aset of static settings from a host identifier to parameters for that host Hub amanager must enter parameters for each host on the server BOOTP does not dynamically allocate IP addresses statically assigning IP addresses to computers has limitations computer moves from one subnet to another or if physical number of computers exceed available IP addresses nowadays it is common place for laptops to be join/leave different subnet networks slide 3 Dynamic Host Configuration Protocol (DHCP) slide 4 DHCP IP address assignment has many advantages over BOOTP clients can obtain all configuration details in a single message IP address, subnet mask, gateway, operating system server IP address IP addresses allocated dynamically when a client boots it broadcasts a DHCP message on the local network client receives (possibly multiple DHCP server offers) selects one server and verifies acceptance different types of IP address assignment manual configuration eg. manager allocates specific addresses per Ethernet address automatic configuration DHCP server allocates a permanent IP address when a client boots dynamic configuration DHCP server loans IP address for a limited time DHCP servers can be configured to manage different clients with the three different IP address assignments can build a highly reliable system by using multiple servers

2 slide 5 DHCP leased IP addresses slide 6 DHCP state transition diagram DHCP specifies a minimum lease period of 1 hour managers may specify default as 1 hour..oo client can release an IP address or request an extension to the lease initialize out:dhcpdiscover in:dhcpnack in:dhcpnack select or expires in: dhcpoffer select offer rebind renew 87.5% request in:dhcpack in:dhcpack bound in:dhcpack lease reaches 50% expiration in: cancel lease out: dhcp release key in: indicates incoming message to client out: client sends message or event causing action Internet routing slide 7 OSPF slide 8 Internet made up of many autonomous systems (AS) each AS is free to choose its own routing algorithm Open Shortest Path First became the IGP standard for the Internet in 1990 see RFC 1247 different companies control different AS s definitions interior gateway protocol arouting algorithm within an AS exterior gateway protocol arouting algorithm outside an AS requirements for OSPF open proprietary algorithm would not do for the Internet must be published in open literature protocol must support variety of metrics physical distance smallest delay reliability

3 OSPF Requirements slide 9 OSPF Requirements slide 10 dynamic algorithm one that adapted to topology changes, quickly support for a type of service realtime traffic vs. reliable transfer of data IP has a type of service field, up until OSPF it was ignored by routing algorithms load balancing network traffic previous routing algorithms used best route ignored second best support for hierarchical systems Internet becoming too large for one router to know every route! support a level ofsecurity support tunneling OSPF Requirements slide 11 Operation of OSPF slide 12 support for variety of network topologies point to point lines between two routers multi access networks with broadcasting eg. Ethernet multi access networks without broadcasting most packet switched WANs multi access network has several routers on it each of which can communicate with the other creates a directed graph where each arc is given a cost delay, throughput and reliability each AS is divided into areas each AS has an area 0 which is the backbone routing is done on the basis of shortest path

4 slide 13 Activity of an OSPF router OSPF Messages slide 14 booting sends a HELLO message to all other routers router periodically floods LINK STATEUPDATE messages to each of it s neighbours these need to be acknowledged and contain sequence number for age and reliability message type description HELLO used to discover who are our neighboughs LINK STATEUPDATEprovides senders cost to neighbough LINK STATEACK acknowledge link state update DATABASE DESC announce the updates LINK STATEREQ requests information from neighbough DATABASE DESCRIPTION messages are issued when a line comes up provides information about the latest sequence number known for each link by the sender aneighbough can request link state information by using LINK STATEREQUEST messages slide 15 Exterior Gateway Routing Protocol: BGP BGP slide 16 within an AS the recommended routing algorithm is OSPF between AS s BGP is used B C D BGP contains rules to allow/disallow policies to allow telephone companies to route customers traffic but noone elses.. E A I F J G H Internet is viewed as a network of BGP routers Fwishes to route to D but does not know requests information from its neighboughs about how they route to D information which F receives Bsays I use BCD Gsays I use GCD Isays I use IFGCD Esays I use EFGCD

5 BGP example slide 17 Fdiscards routing information from I and E as they both route through F any routing method that violated political constraints are also dismissed it then chooses to route packets via G or B further reading RFC 1654 and RFC 1268