Data and Computer Communications Ninth Edition by William Stallings Chapter 19 – Internetwork Operation Data and Computer Communications, Ninth Edition by William Stallings, (c) Pearson Education - Prentice Hall, 2011

Internetwork Operation Prior to the recent explosion of sophisticated research, scientists believed that birds required no special awareness or intelligence to perform their migrations and their navigational and homing feats. Accumulated research shows that in addition to performing the difficult tasks of correcting for displacement (by storms, winds, mountains, and other hindrances), birds integrate an astonishing variety of celestial, atmospheric, and geological information to travel between their winter and summer homes. In brief, avian navigation is characterized by the ability to gather a variety of informational cues and to interpret and coordinate them so as to move closer toward a goal. —The Human Nature of Birds, Theodore Barber

Multicasting  sending packet to addresses referring to group of hosts on one or more networks multimedia “broadcast” multimedia “broadcast” teleconferencing teleconferencing database database distributed computing distributed computing real time workgroups real time workgroups

LAN Multicast  LAN multicast is easy send to IEEE 802 multicast MAC address send to IEEE 802 multicast MAC address #Ethernet #Ethernet #Ethernet #Ethernet those in multicast group will accept it those in multicast group will accept it only single copy of packet is needed only single copy of packet is needed  a transmission from any one station is received by all other stations on LAN easy!

Example Configuration

Broadcast / Multiple Unicast / Multicast

Traffic Generated by Various Multicasting Strategies

Multicast Example

Requirements for Multicasting  router may have to forward more than one copy of packet  need convention to identify multicast addresses (IPv4 Class D, IPv6)  nodes translate between IP multicast addresses and list of networks containing group members  router must translate between IP multicast address and LAN multicast address Cont…

Requirements for Multicasting  On the “leaves” of the spanning tree, packets are formed using Ethernet multicast address  Ex. If one computer joined the class D address, AAA.BBB.CCC.DDD, then the Ethernet multicast address E BBB CCC DDD will be used (AAA, BBB, CCC and DDD being single bytes) – more exactly, it is the low 23 bits of the IP address that is copied… low 23 bits of the IP address that is copiedlow 23 bits of the IP address that is copied Cont…

Requirements for Multicasting 1. mechanism required for hosts to join and leave multicast group 2. routers must exchange information which networks include members of given group which networks include members of given group sufficient information to work out shortest path to each network sufficient information to work out shortest path to each network 3. routing algorithm to calculate shortest path 4. routers must determine routing paths based on source and destination addresses

Spanning Tree from Router C to Multicast Group

How to get/select a multicast address « Well-known » addresses : to Internet-wide addresses : to For local use : to addresses.xhtml

Internet Group Management Protocol (IGMP)  RFC 3376 used to exchange multicast group information between hosts & routers on a LAN  hosts send messages to routers to subscribe and unsubscribe from multicast group  routers check which multicast groups are of interest to which hosts  IGMP currently at version 3

Operation of IGMP v1 & v2  IGMPv1 hosts could join group hosts could join group routers used timer to unsubscribe members routers used timer to unsubscribe members  IGMPv2 enabled hosts to unsubscribe  operational model: receivers have to subscribe to groups receivers have to subscribe to groups sources do not have to subscribe to groups sources do not have to subscribe to groups any host can send traffic to any multicast groupany host can send traffic to any multicast group  problems: spamming of multicast groups establishment of distribution trees is problematic finding globally unique multicast addresses difficult

IGMP v3  addresses weaknesses by: allowing hosts to specify list from which they want to receive traffic allowing hosts to specify list from which they want to receive traffic blocking traffic from other hosts at routers blocking traffic from other hosts at routers allowing hosts to block packets from sources that send unwanted traffic allowing hosts to block packets from sources that send unwanted traffic

IGMP Message Formats Membership Query  IP datagrams sent by multicast router  Three subtypes: general query (which groups have members on an attached network), group-specific query (to learn if a particular group has any members on an attached network), group-and-source specific query (to learn if any attached device desires reception of packets)  Data part of the IP datagram is structured as follows:

Membership Query Fields type max response time checksum group address S flag QRV (querier's robustness variable) QQIC (querier's querier interval code) number of sources source addresses

IGMP Message Formats Membership Report (to join a group…) Next page

IGMP Message Formats Group Record

IGMP Operation - Joining IIIIGMP host wants to make itself known as group member to other hosts and routers on LAN IIIIGMPv3 can signal group membership with filtering capabilities with respect to sources EXCLUDE mode – all members except those listed INCLUDE mode – only from group members listed to join, send IGMP membership report message address field multicast address of group sent in IP datagram current group members receive & learn new member routers listen to all IP multicast addresses to hear all reports

IGMP Operation – Keeping Lists Valid routers periodically issue IGMP general query message in datagram with all- hosts multicast address hosts must read such datagrams hosts respond with report message router doesn’t know every host in a group needs to know at least one group member still active each host in group sets timer with random delay host hearing another report cancels own if timer expires, host sends report only one member of each group reports to router

IGMP Operation - Leaving  host leaves group by sending a leave group message to the all-routers static multicast address sends a membership report message with EXCLUDE option and null list of source addresses sends a membership report message with EXCLUDE option and null list of source addresses  router determines if have any remaining group members using group-specific query message

Group Membership with IPv6  IGMP defined for IPv4 uses 32-bit addresses uses 32-bit addresses  IPv6 internets need functionality  IGMP functions included in Internet Control Message Protocol v6 (ICMPv6) ICMPv6 has functionality of ICMPv4 + IGMP ICMPv6 has functionality of ICMPv4 + IGMP  ICMPv6 includes group-membership query and group-membership report message

Routing Protocols

 routers receive and forward packets  make decisions based on knowledge of topology and traffic / delay conditions  use dynamic routing algorithm we must distinguish between routing information - about topology and delays routing algorithm - makes routing decisions based on information

Autonomous Systems (AS)  a group of routers and networks managed by a single organization (Ex. : UQAC)  exchange information via a common routing protocol  form a connected network at least one path between any pair of nodes, except in times of failure at least one path between any pair of nodes, except in times of failure

Interior Router Protocol (IRP) & Exterior Routing Protocol (ERP)  may have more than one AS in internet routing algorithms & tables may differ between them routing algorithms & tables may differ between them  routers need information on networks outside their own AS use an exterior router protocol (ERP) for this use an exterior router protocol (ERP) for this supports summary information on AS reachability supports summary information on AS reachability interior router protocol (IRP) passes routing information between routers within AS can be tailored to specific applications needs detailed model of network to function

Application of IRP and ERP

Approaches to Routing 1) Distance-vector  each node (router or host) exchanges information with neighboring nodes  first generation routing algorithm for ARPANET  each node maintains vector of link costs for each directly attached network, as well as distance and next-hop vectors for each destination  requires transmission of considerable information by routers (neighbor to neighbor…) distance vector and estimated path costs distance vector and estimated path costs  changes could take a long time to propagate

Approaches to Routing 2) Link-state  designed to overcome drawbacks of distance-vector  each router determines link cost on each of its interfaces  advertises set of link costs to all other routers in topology (not just to neighboring routers)  if link costs change, router advertises new values  each router constructs topology of entire configuration can calculate shortest path to each destination can calculate shortest path to each destination used to construct routing table with first hop to each destination used to construct routing table with first hop to each destination  do not use distributed routing algorithm, but any suitable algorithm to determine shortest paths  Open Shortest Path First (OSPF) is a link-state protocol

Disadvantages of Exterior Routing Protocols  link-state and distance-vector are not effective for exterior router protocol distance- vector assumes routers share common distance metric different ASs may have different priorities and needs have no information on AS’s visited along route link-state different ASs may use different metrics and have different restrictions flooding of link state information to all routers is unmanageable

Exterior Router Protocols -> use Path-vector  Alternative : path-vector routing protocol provides information about : provides information about : destinations -> which networks can be reached by a given routerdestinations -> which networks can be reached by a given router paths -> ASs crossed to get therepaths -> ASs crossed to get there Next routerNext router does not include distance or cost estimate does not include distance or cost estimate dispenses with (get rid of) concept of routing metrics dispenses with (get rid of) concept of routing metrics  have list of all ASs visited on a route  enables router to perform policy routing eg. avoid path to avoid transiting particular AS eg. avoid path to avoid transiting particular AS eg. link speed, capacity, tendency to become congested, and overall quality of operation, security eg. link speed, capacity, tendency to become congested, and overall quality of operation, security eg. minimizing number of transit ASs eg. minimizing number of transit ASs

Border Gateway Protocol (BGP)  developed for use with TCP/IP internets  preferred EGP of the Internet  uses messages sent over TCP connection  current version is BGP-4 (RFC1771)  functional procedures neighbor acquisition - when two routers agree to exchange information neighbor acquisition - when two routers agree to exchange information neighbor reachability - to maintain relationship neighbor reachability - to maintain relationship network reachability - to update database of routes network reachability - to update database of routes

(BGP Messages)

(Message Types - Open and Keepalive)  router makes TCP connection to neighbor  Keep Alive message to tell other routers that this router is still here to tell other routers that this router is still here open message sent by connection initiator includes proposed hold time receiver uses minimum of own/sent hold time max time between Keepalive and/or Update

(Message Types – Update)  withdraw route identified by destination IP address update message conveys two information types information about single routes through internet list of routes being withdrawn information on a route uses three fields Network Layer Reachability Information (NLRI) Total Path Attributes Length Path Attributes

(Message Types – Update)  Origin - IGP or EGP  AS_Path - list of AS traversed  Next_hop - IP address of border router  Multi_Exit_Disc - info on routers internal to AS  Local_pref - inform routers in AS of route preference  Atomic_Aggregate, Aggregator - implement route aggregation to reduce amount of information

(AS_Path and Next_Hop Use)  AS_Path used to implement routing policies used to implement routing policies eg. to avoid a particular AS, security, performance, quality, number of AS crossedeg. to avoid a particular AS, security, performance, quality, number of AS crossed  Next_Hop only a few routers implement BGP responsible for informing outside routers of routes to other networks in AS

(Notification Message)  sent when some error condition is detected  message header error  open message error  update message error  hold time expired  finite state machine error  cease

BGP Routing Information Exchange  within AS, a router builds topology picture using IGP  router issues Update message to other routers outside AS using BGP  these routers exchange information with other routers in other AS AS_Path field used to prevent loops AS_Path field used to prevent loops  routers must then decide best routes

Open Shortest Path First (RFC2328)  IGP of Internet  replaced Routing Information Protocol (RIP)  uses least cost based on user cost metric uses Link State Routing Algorithm each router keeps list of state of local links to network transmits update state info little traffic as messages are small and not sent often topology stored as directed graph vertices or nodes (router, transit or stub network) edges (between routers or router to network)

Example OSPF AS

Directed Graph of AS (compare this slide with previous one)

(Shortest path first) SPF Tree for Router 6 (compare this slide with previous one and observe paths between R6 and R4, and between R6 and R7)

Similar to Dijkstra’s algorithm See illustration (animated)

Routing Table for R6

Mobile IP  enables computers to maintain Internet connectivity (same IP address) while moving from one Internet attachment point to another (not to be confused with temporary IP address allocation)  particularly suited for wireless connections  mobile implies: a user is connected to one or more applications across the Internet a user is connected to one or more applications across the Internet the user’s point of attachment changes dynamically the user’s point of attachment changes dynamically all connections are automatically maintained despite the change all connections are automatically maintained despite the change

Operation of Mobile IP  In a TCP/IP network, routers use the IP address in an IP datagram to perform routing  network portion is used to move a datagram to the network the target computer is attached to  final router uses the host portion to deliver to the destination

Mobile IP Scenario (triangular routing)

Basic Capabilities of Mobile IP Mobile IP includes three basic capabilities Discovery a discovery procedure is used to identify prospective home and foreign agents Registration authenticated registration procedure is used Tunneling forwards IP datagram from a home address to a care-of address

Mobile IP Protocol Support

Mobile IP Terminology (RFC 3334) Mobile IP Terminology (RFC 3334)

(Discovery)  similar to the router advertisement process defined in ICMP  mobile node is responsible for an ongoing discovery process  home or foreign network  listens for agent advertisement message compares IP address with home address compares IP address with home address If these do not match the mobile node is on a foreign network If these do not match the mobile node is on a foreign network

(Use of Lifetime Field) upon receipt of an agent advertisement from a foreign agent the mobile node records the lifetime field as a timer if timer expires before receipt of another advertisement, node assumes it lost contact if node has received an advertisement that is not expired, node registers with the new agent otherwise, node uses agent solicitation to find an agent

(Use of Network Prefix) mobile node checks if newly received agent advertisement is on the same network as the node’s current care-of address if it is not, the node assumes it moved and registers with advertisement the node has just received

(Co-Located Address)  node may move to a network that has no foreign agents or foreign agents are busy may act as its own foreign agent by using a co- located care-of address may act as its own foreign agent by using a co- located care-of address  co-located care-of address is an IP address that is associated with the node’s current interface to a network can dynamically acquire a temporary IP address can dynamically acquire a temporary IP address co-located address may be owned by the node co-located address may be owned by the node

(Registration)  once care-of address is acquired the mobile node needs to request the home agent forward its IP traffic  registration process:  if node is using a co-located care-of address it registers directly with its home agent node sends a registration request to the foreign agent requesting forwarding service foreign agent relays request to home agent home agent accepts or denies request foreign agent relays reply to node

(Registration Messages)  registration operation uses two types of messages carried in UDP segments  registration request message includes: one-bit flags one-bit flags home address field home address field home agent field home agent field care-of address field care-of address field identification field identification field  registration reply message includes: acceptance code acceptance code reason for denial reason for denial

(Registration Security)  mobile IP is designed to resist two types of attacks: node pretends to be a foreign agent and sends registration request to home agent to divert traffic node pretends to be a foreign agent and sends registration request to home agent to divert traffic malicious agent may replay old registration messages effectively cutting node from the network malicious agent may replay old registration messages effectively cutting node from the network

(Message Authentication)  message authentication is used to protect against registration message attacks  authentication extension includes the following fields: security parameter index (SPI) security parameter index (SPI) authenticator authenticator three types of authentication extensions: mobile-home mobile-foreign foreign-home

Tunneling  once a mobile node is registered with a home agent the agent must be able to intercept IP datagrams to be forwarded  references ARP as a possible mechanism  home agent steals the identity of the mobile node in order to capture packets destined for that node  encapsulation for Mobile IP: IP-within-IP (RFC 2003) IP-within-IP (RFC 2003) Minimal (RFC 2004) Minimal (RFC 2004) generic routing (RFC 1701) generic routing (RFC 1701)

IP-Within-IP Encapsulation (ref.: Cisco document) Cisco documentCisco document

Minimal Encapsulation  the new header is inserted between the original IP header and the original IP payload  includes the following fields:  fields in the original IP header modified to form the new outer IP header are:  Total length  Protocol  Header checksum  Source and destination addresses  Destination address Protocol S Header checksum Original source and destination addresses

Summary  multicasting IGMP IGMP  routing protocols BGP, OSPF BGP, OSPF  mobile IP operation, discovery, registration, tunneling operation, discovery, registration, tunneling