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Instructor: Dr. Son T. Vuong Email: vuong@cs.ubc The World Connected

University of British Columbia CICS 515 (Part 2) Computer Networks Lecture 5b-c – IPv6 and Other Protocols. Instructor: Dr. Son T. Vuong Email: vuong@cs.ubc.ca The World Connected. IPv6. Initial motivation: 32-bit address space soon to be completely allocated. Additional motivation:

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Instructor: Dr. Son T. Vuong Email: vuong@cs.ubc The World Connected

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  1. University of British ColumbiaCICS 515 (Part 2)Computer NetworksLecture 5b-c – IPv6 and Other Protocols Instructor: Dr. Son T. Vuong Email: vuong@cs.ubc.ca The World Connected

  2. IPv6 • Initial motivation:32-bit address space soon to be completely allocated. • Additional motivation: • header format helps speed processing/forwarding • header changes to facilitate QoS IPv6 datagram format: • fixed-length 40 byte header • no fragmentation specified in basic header

  3. IPv6 Header (Cont) Priority: identify priority among datagrams in flow Flow Label: identify datagrams in same “flow.” (concept of“flow” not well defined). Next header: identify upper layer protocol for data

  4. Other Changes from IPv4 • Checksum:removed entirely to reduce processing time at each hop • Options: allowed, but outside of header, indicated by “Next Header” field • ICMPv6: new version of ICMP • additional message types, e.g. “Packet Too Big” • multicast group management functions

  5. Transition From IPv4 To IPv6 • Not all routers can be upgraded simultaneous • no “flag days” • How will the network operate with mixed IPv4 and IPv6 routers? • Tunneling: IPv6 carried as payload in IPv4 datagram among IPv4 routers

  6. Flow: X Src: A Dest: F data Flow: X Src: A Dest: F data Flow: X Src: A Dest: F data Flow: X Src: A Dest: F data F E B A D C F E B A Src:B Dest: E Src:B Dest: E Dual IPv6/IPv4 Router Dual IPv6/IPv4 Router Tunneling tunnel Logical view: IPv6 IPv6 IPv6 IPv6 Physical view: IPv6 IPv6 IPv6 IPv6 IPv4 IPv4 A-to-B: IPv6 E-to-F: IPv6 B-to-C: IPv6 inside IPv4 B-to-C: IPv6 inside IPv4

  7. IPv6 – Peer Instruction – Question 5.2 IPv6 supports the following features: A. 128-bit IP address B. Auto-configuration (plug-and-play) (stateless) as well as dynamic IP address via a DHCPv6 server (stateful) C. More options via extension headers including Jumbogram of greater than 64KB D. Efficient header processing E. All the above F. A, B and C

  8. IPv6 – Peer Instruction – Question 5.3 An IPv6 datagram is 80,000 bytes. What extension header must be used? A.Destination option B.Fragmentation C.Authentication D. Hop-by-hop E. None of the above

  9. IPv6 – Peer Instruction – Question 5.4 The IPv6 jumbogram option gives rise to the following issues: A.Fragmentation B.16-bit length of UDP C. 16-bit MSS option of TCP D. Checksum calculation E. All of the above F. B and C

  10. Ch 4: Network Layer and Routing • The IP Protocol • IP Format, Addressing, fragmentation, • Internet Control Protocols (ICMP) • Routing • RIP (Routing Information Protocol) • OSPF (Open Shortest Path First) • The Interior Gateway Routing Protocol • BGP – The Exterior Gateway Routing Protocol • IPv6 • Internet Multicasting • Mobile IP

  11. What’s next ? What have we covered? • IPv4, IPv6 • Internet Control Message Protocol (ICMP) • Address resolution (ARP) • Getting (dynamic) addresses (DHCP) • DNS • Routing protocols (RIP, OSPF, BGP)

  12. University of British ColumbiaCICS 515 (Part 2)Computer NetworksLecture 5c – ICMP, ARP, DHCP, DNS Instructor: Dr. Son T. Vuong Email: vuong@cs.ubc.ca The World Connected

  13. Lect. 5c – Other IP protocols ICMP, ARP, DHCP (Sect. 4.4.3, 5.4)DNS (Sect. 2.5 ) Internet Control Message Protocol (ICMP)(Sect 4.4.3) Address Resolution (ARP) (Sect 5.4) Dynamic IP address assignment (DHCP) (Sect 5.4) Domain Name System (DNS) (Sect2.5)

  14. Used by hosts & routers to communicate network-level information error reporting: unreachable host, network, port, protocol echo request/reply (used by ping) Network-layer “above” IP: ICMP msgs carried in IP datagrams ICMP message: type (1B), code (1B), checksum (2B) plus part of IP datagram causing error (header + first 8 bytes of data) ICMP: Internet Control Message ProtocolRFC 792

  15. ICMP datagram structure • ICMP msgs carried in IP datagrams • ICMP data contains part of IP datagram causing error (IP header + first 8 bytes of data)

  16. ICMP: Internet Control Message Protocol • TypeCodedescription • 0 0 echo reply (ping) • 3 0 dest. network unreachable • 3 1 dest host unreachable • 3 2 dest protocol unreachable • 3 3 dest port unreachable • 3 6 dest network unknown • 3 7 dest host unknown • 0 source quench (congestion control - not used) • 0-3 redirect a host to a better router • 8 0 echo request (ping) • 9 0 route advertisement • 10 0 router discovery (solicitation) • 11 0 TTL expired • 12 0 bad IP header

  17. 3 probes 3 probes 3 probes “Real” Internet delays and routes • What do “real” Internet delay & loss look like? • traceroute (tracert) program: provides delay measurement from source to router along end-end Internet path towards destination. For all i: • sends three UDP packets that will reach router i on path towards destination • router i will return packets to sender • sender times interval between transmission and reply.

  18. Source sends series of UDP segments to dest First has TTL =1 Second has TTL=2, etc. Unlikely port number When nth datagram arrives to nth router: Router discards datagram And sends to source an ICMP message (type 11, code 0) Message includes name of router& IP address When ICMP message arrives, source calculates RTT Traceroute does this 3 times Stopping criterion UDP segment eventually arrives at destination host Destination returns ICMP “port unreachable” packet (type 3, code 3) When source gets this ICMP, stops. Traceroute and ICMP

  19. Address Resolution Protocol (ARP) • How do we convert the IP address of each node (either the destination node, or a router) into the address on the local network? E.g. IP -> Ethernet. • Each machine keeps a mapping of IP address to physical addresses in a cache. • E.g. cascade.cs.ubc.ca 08:00:20:79:70:f5 dragon.cs.ubc.ca 08:00:09:27:b4:73 etc… • What if the mapping isn’t known, or has expired? Send an ARP (Address Resolution Protocol) broadcast message over the network.

  20. ARP Packet Format 0 8 16 31 Hardware type = 1 ProtocolType = 0x0800 HLen = 48 PLen = 32 Operation SourceHardwareAddr (bytes 0-3) SourceHardwareAddr (bytes 4-5) SourceProtocolAddr (bytes 0-1) SourceProtocolAddr (bytes 2-3) TargetHardwareAddr (bytes 0-1) TargetHardwareAddr (bytes 2-5) TargetProtocolAddr (bytes 0-3)

  21. ARP Fields • Request format • HardwareType - Type of physical network (e.g., Ethernet) • ProtocolType - Type of higher layer protocol (e.g., IP) • HLEN & PLEN - Length of physical and protocol addresses (measured in bits) • Operation - Request for an address, or response to a request. • Source/Target Physical/Protocol addresses

  22. ARP Comments • An ARP packet sits at the same level in the protocol graph as an IP packet. However ARP service is used by IP; thus ARP can also be viewed as a sublayer below IP. • ARP table entries timeout in about 10 minutes • Update the ARP table with information about the source when you are the target. Hence, both source/target physical/protocol addresses are in the packet.

  23. Dynamic Host Configuration Protocol (DHCP) How does a host get an IP address? • Fixed – assigned • Dynamic – changeable: via DHCP • why?

  24. Dynamic Host Configuration Protocol (DHCP) • DHCP allows config info (IP address etc) stored in DHCP server to be retrieved automatically by each host when booted or connected to network (via broadcast DHCPDiscover message) • that is, special IP address 255.255.255.255 • ignored by everyone except the DHCP server

  25. DHCP (cont’d) • DHCP also allows dynamic assignment of IP addresses to hosts (DHCP server maintains a pool of available IP addresses to lease to host and host need to renew lease periodically). • It is not desirable to have a DHCP server on every network – instead, uses a relay agent for each network. • Relay agent unicasts DHCP request to server

  26. Unicast to server DHCP DHCP Other networks relay server Broadcast Host DHCP with relay agent

  27. Operation HT ype HLen Hops Transaction ID (Xid) No. of secs Flags/unused Client IP addr Your IP addr (yiaddr) Server IP addr Gateway IP addr Client hardware addr (chaddr) (16 bytes) Server name (64 bytes) file (128 bytes) options DHCP Packet Format DHCP is derived from an earlier protocol called BOOTP

  28. DHCP (cont’d) • Sent using UDP • Client puts hardware address in chaddr • Server replies with IP address in yiaddr (and other config info, e.g. gateway addr, server IP address, etc) • Types of DHCP packets (spec’d as options): • Discover, Offer, Request, Decline, Ack, Nack, Release • Scalability/manageability -- recurring theme (via relay/proxy)

  29. Request Request (or Decline) Ack (or Nack) Ack (or Nack) DHCP Scenario DHCP Client DHCP Server Discover Offer . . . . . . Release

  30. Layering Relationships between ICMP, ARP, DHCP and IP, UDP • ICMP/IP • IPcalls ARP/Link(Ethernet) • DHCP(BOOTP) / UDP(67/68) (for simple configinfo) DHCP(BOOTP) / TFTP/UDP(69) (to get config file)

  31. DNS: Domain Name System

  32. 2.1 Principles of network applications 2.2 Web and HTTP 2.3 FTP 2.4 Electronic Mail SMTP, POP3, IMAP 2.5 DNS 2.6 P2P file sharing 2.7 Socket programming with TCP 2.8 Socket programming with UDP 2.9 Building a Web server Chapter 2: Application layer

  33. Domain Name System (DNS) Overview • What do names do? • identify objects • help locate objects • define membership in a group • specify a role • convey knowledge of a secret • Name space • defines set of possible names • consists of a set of name to value bindings

  34. Properties • Names versus addresses • Location transparent versus location-dependent • Flat versus hierarchical • Global versus local • Absolute versus relative • By architecture versus by convention • Unique versus ambiguous

  35. Examples • Hosts cheltenham.cs.princeton.edu 192.12.69.17 192.12.69.17 80:23:A8:33:5B:9F • Files /usr/llp/tmp/foo (server, fileid) • Users Larry Peterson llp@cs.princeton.edu

  36. Summary of “Naming” or identification • Domain name: a name that makes sense to a human -- e.g. “cascade.cs.ubc.ca” • IP address: an identifier that makes sense to hosts and routers -- e.g. “142.103.7.7” • Physical address: an identifier that makes sense to the interface card -- e.g. “8:0:2b:e4:b1:2”

  37. People: many identifiers: SSN, name, passport # Internet hosts, routers: IP address (32 bit) - used for addressing datagrams “name”, e.g., www.yahoo.com - used by humans Q:map between IP addresses and name ? Domain Name System: distributed database implemented in hierarchy of many name servers application-layer protocol host, routers, name servers to communicate to resolvenames (address/name translation) note: core Internet function, implemented as application-layer protocol complexity at network’s “edge” DNS: Domain Name System

  38. Why not centralize DNS? single point of failure traffic volume distant centralized database Maintenance doesn’t scale! DNS services Hostname to IP address translation Host aliasing Canonical and alias names Mail server aliasing Load distribution Replicated Web servers: set of IP addresses for one canonical name DNS: Domain Name System

  39. Examples (cont) User 1 2 vuong @ cs.ubc.ca cs.ubc.ca • Mailboxes • Services nearby ps printer with short queue and 2MB Name Mail server program 4 142.103.7.51 142.103.7.51 3 TCP 142.103.7.51 5 IP

  40. Domain Naming System • Hierarchy • Name chinstrap.cs.princeton.edu

  41. Distributed, Hierarchical Database Root DNS Servers org DNS servers edu DNS servers com DNS servers poly.edu DNS servers umass.edu DNS servers pbs.org DNS servers yahoo.com DNS servers amazon.com DNS servers Client wants IP for www.amazon.com; 1st approx: • Client queries a root server to find com DNS server • Client queries com DNS server to get amazon.com DNS server • Client queries amazon.com DNS server to get IP address for www.amazon.com

  42. Root name server … UBC Cisco name server name server … CS ECE name server name server Name Servers Root name servers Top Level Domain (TLD) Servers • Partition hierarchy into zones edu com gov mil org net uk fr … … … … … princeton mit cisco yahoo nasa nsf arpa navy acm ieee cs ee physics ux01 ux04 • Each zone corresponds to an admin authority (implemented by two or more name servers for redundancy) Authoritative ServersLocal Name Servers (LNS)

  43. contacted by local name server that can not resolve name root name server: contacts authoritative name server if name mapping not known gets mapping returns mapping to local name server DNS: Root name servers a Verisign, Dulles, VA c Cogent, Herndon, VA (also Los Angeles) d U Maryland College Park, MD g US DoD Vienna, VA h ARL Aberdeen, MD j Verisign, ( 11 locations) k RIPE London (also Amsterdam, Frankfurt) i Autonomica, Stockholm (plus 3 other locations) e NASA Mt View, CA f Internet Software C. Palo Alto, CA (and 17 other locations) m WIDE Tokyo 13 root name servers worldwide b USC-ISI Marina del Rey, CA l ICANN Los Angeles, CA

  44. TLD 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. • Verisign controls .com and .net TLDs • Many companies act as intermediaries • 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 provider

  45. Local 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.

  46. Host at cis.poly.edu wants IP address for gaia.cs.umass.edu local DNS server dns.poly.edu Example: Iterative queries root DNS server 2 3 TLD DNS server 4 5 iterative query: contacted server replies with name of server to contact “I don’t know this name, but ask this server” 6 7 1 8 authoritative DNS server dns.cs.umass.edu requesting host cis.poly.edu gaia.cs.umass.edu

  47. local DNS server dns.poly.edu Recursive queries root DNS server recursive query: • puts burden of name resolution on contacted name server • heavy load? 2 3 6 7 TLD DNS server 4 5 1 8 authoritative DNS server dns.cs.umass.edu requesting host cis.poly.edu gaia.cs.umass.edu

  48. once (any) name server learns mapping, it cachesmapping 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.html DNS: caching and updating records

  49. DNS: distributed db storing resource records(RR) Type = NS name is domain (e.g. foo.com) value is IP address of authoritative name server for this domain RR format: (name, value, type, ttl) DNS records • Type = A • name is hostname • value is IP address • Type = CNAME • name is alias name for some “cannonical” (the real) name www.ibm.comis really servereast.backup2.ibm.com • value is cannonical name • Type = MX • value is name of mailserver associated with name

  50. Example: Root Server (princeton.edu, cit.princeton.edu, NS, IN) [in the Princeton domain] (cit.princeton.edu, 128.196.128.233, A, IN) (cisco.com, thumper.cisco.com, NS, IN) [in the Cisco domain] (thumper.cisco.com, 128.96.32.20, A, IN) …

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