1Application ProtocolsEECS 122: Lecture 6Department of Electrical Engineering and Computer SciencesUniversity of CaliforniaBerkeleyFebruary 2, 2006EECS122 Lecture 6 (AKP)2Today Adminstrivia The last two lectures have exposed you to building programs and simulations of networks Today we focus on specific applications and protocols DNS HTTP SMTP Lots of details but focus on the concepts…2February 2, 2006EECS122 Lecture 6 (AKP)3Where do Application Protocols Run?BGP HTTP RTP DNSTCP UDPIPEthernet FDDI Token Etc.NetworkIPTCP UDPApplicationFebruary 2, 2006EECS122 Lecture 6 (AKP)4Where do Application Protocols Run? Host-Host: HTTP, SMTP Host-Network: DNS Network-Network: Routing Protocols (e.g. OSPF)The Core providesa network service to the hostsHostHost3February 2, 2006EECS122 Lecture 6 (AKP)5Internet transport protocols servicesTCP service: connection-oriented: setup required between client and server processes reliable transport between sending and receiving process flow control: sender won’t overwhelm receiver congestion control: throttle sender when network overloaded does not provide: timing, minimum bandwidth guaranteesUDP service: unreliable data transfer between sending and receiving process does not provide: connection setup, reliability, flow control, congestion control, timing, or bandwidth guarantee February 2, 2006EECS122 Lecture 6 (AKP)6Internet apps: application, transport protocolsApplicatione-mailremote terminal accessWeb file transferstreaming multimediaInternet telephonyApplicationlayer protocolSMTP [RFC 2821]Telnet [RFC 854]HTTP [RFC 2616]FTP [RFC 959]proprietary(e.g. RealNetworks)proprietary(e.g., Vonage,Dialpad)Underlyingtransport protocolTCPTCPTCPTCPTCP or UDPtypically UDP4February 2, 2006EECS122 Lecture 6 (AKP)7Domain Name Service Resolves a host name names into an IP address Why host names? To organize machines Eg. robotics.eecs.berkeley.edu This conveys more information to humans than 128.32.48.234 Why IP addresss? The network needs an address to route Host Names yield information to people and IP addresses yield information to routersFebruary 2, 2006EECS122 Lecture 6 (AKP)8DNS: History Initially all host-addess mappings were in a file called hosts.txt (in /etc/hosts) Changes were submitted to SRI by email New versions of hosts.txt were ftp’d periodically from SRI An administrator could pick names at their discretion As the internet grew this system broke down because SRI couldn’t handled the load The system was unreliable since there was a single point of contact Names were not unique Many hosts had inaccurate copies of hosts.txt Internet growth was threatened!5February 2, 2006EECS122 Lecture 6 (AKP)9DNS Features Hierarchical Namespace Distributed architecture for storing names Nameservers assigned zones of the hierarchical namespace Backup servers available for redundancy Administration divided along the same hierarchy DNS client is simple: Resolver Client server interaction on UDP Port 53 (but can use TCP if desired)February 2, 2006EECS122 Lecture 6 (AKP)10Hierarchical Namespace The first level names are called “Top Level Domains” Depth of tree is arbitrary (limit 128) Domains are subtrees E.g. berkeley.edu and eecs.berkeley.edu Name collision avoided E.g. berkeley.edu and berkeley.comrooteducomgov milorgnet uk frberkeleymiteecssimsargus6February 2, 2006EECS122 Lecture 6 (AKP)11Hierarchical Administrationrooteducomgov milorgnet uk frberkeleymiteecssimsargusrooteducomgov milorgnet uk frberkeleyeecssimsA zone corresponds to an administrative authority that is responsible for that portion of the hierarchyFebruary 2, 2006EECS122 Lecture 6 (AKP)12Hierarchical Server Organization Each server has authority over a portion of the hierarchy A server maintains only a subset of all names Each server contains all the records for the hosts in its zone Each server needs to know other servers that are responsible for the other portions of the hierarchy Every server knows the root Root server knows about all top-level domains7February 2, 2006EECS122 Lecture 6 (AKP)13TLD and Authoritative Servers Top-level domain (TLD) servers: responsible for com, org, net, edu, etc, and all top-level country domains uk, fr, ca, jp. Network solutions maintains servers for com TLD Educause for edu TLD Authoritative DNS servers: organization’s DNS servers, providing authoritative hostname to IP mappings for organization’s servers (e.g., Web and mail). Can be maintained by organization or service providerFebruary 2, 2006EECS122 Lecture 6 (AKP)14Local Name Server Does not strictly belong to hierarchy Each ISP (residential ISP, company, university) has one. Also called “default name server” When a host makes a DNS query, query is sent to its local DNS server Acts as a proxy, forwards query into hierarchy.8February 2, 2006EECS122 Lecture 6 (AKP)15How does a name get resolved Query “walks” its way up and down the hierarchy Iterated query I don’t know, but here’s who to ask next Recursive query I don’t know right now, but I’ll get back to you…February 2, 2006EECS122 Lecture 6 (AKP)16requesting hostlids.mit.edutop.eecs.berkeley.eduroot DNS serverlocal DNS serverdns.mit.edu123456authoritative DNS serverns1.berkeley.edu78TLD DNS serverIterated Query Host at lids.mit.eduwants IP address for top.eecs.berkeley.edu. “I don’t know, but here’s who to ask next”9February 2, 2006EECS122 Lecture 6 (AKP)17requesting hostlids.mit.edutop.eecs.berkeley.eduroot DNS serverlocal DNS serverdns.mit.edu123456authoritative DNS serverns1.berkeley.edu78Recursive Query Host at lids.mit.eduwants IP address for top.eecs.berkeley.edu. I don’t know right now, but I’ll get back to you…TLD DNS serverFebruary 2, 2006EECS122 Lecture 6 (AKP)18DNS: caching and updating records once (any) name server learns mapping, it caches mapping cache entries timeout (disappear) after some time TLD servers typically cached in local name servers Thus root name servers not often visited update/notify mechanisms under design by IETF RFC 2136 http://www.ietf.org/html.charters/dnsind-charter.html10February 2, 2006EECS122 Lecture 6 (AKP)19DNS recordsDNS: distributed db storing resource records (RR) Type=NS name is domain (e.g. foo.com) value is
View Full Document
Unlocking...