Internet Foreleser Carsten Griwodz Email griffifi uio no

Internet Foreleser: Carsten Griwodz Email: griff@ifi. uio. no 11. Mar. 2004 1 INF-3190: Internet

Address Resolution 11. Mar. 2004 2 INF-3190: Internet

Address Resolution n Addressing levels Logical address e. g. www. ifi. uio. no Internet address e. g. 129. 31. 65. 7 Address resolution Domain Name System ? Netadapter address e. g. Ethernet address 00: 08: 74: 35: 2 b: 0 a n Host identification and routing specification within a subnetwork n based on the (local) physical network addresses of the end systems n n e. g. station address of the adapter card Problem n n Different address styles for different layer 2 protocols IP address must be mapped onto the physical network address, 48 bit for Ethernet n n 11. Mar. 2004 Direct mapping possible for IPv 6 But impossible for IPv 4 3 INF-3190: Internet

Address Resolution: Methods n Address resolution in n Source ES, if destination ES is local (direct routing) Gateway, if destination ES is not local Solutions n Direct homogeneous Addressing n if the physical address can be changed by the user n n n physical address = Hostid of the IP address Only possible if physical address is also longer than hostid If the physical address is pre-defined or if it has to have a different format, one of the following has to be used n a mapping table from the configuration data base (IPaddr HWaddr), n n n the Address Resolution Protocol (ARP) n 11. Mar. 2004 e. g. in the Gateway, may become maintenance nightmare mainly applied in LANs with broadcasting facility 4 INF-3190: Internet

Address Resolution Protocol (ARP) n Process n Broadcast ARP request datagram on LAN n n Every machine on LAN receives this request and checks address Reply by sending ARP response datagram n n n including receiver’s IP address (desired value) sender’s physical (HW) and IP address (IP) machine which has requested address responses including the physical address Enter the pair (I, P) into buffer for future requests 11. Mar. 2004 5 INF-3190: Internet

Address Resolution Protocol (ARP) H H H ARP Request source @IP: 9. 228. 50. 8 @HW: 0 xaa target @IP: 9. 228. 50. 3 @HW: 0 xa 3 e ARP Response source @IP: 9. 228. 50. 3 @HW: 0 xa 3 e target @IP: 9. 228. 50. 8 @HW: 0 xaa 11. Mar. 2004 6 INF-3190: Internet

Address Resolution Protocol (ARP) n Process n Broadcast ARP request datagram on LAN n n Every machine on LAN receives this request and checks address Reply by sending ARP response datagram n n including receiver’s IP address (desired value) sender’s physical (HW) and IP address (IP) machine which has requested address responses including the physical address Enter the pair (I, P) into buffer for future requests Refinement n n n The receiver of the ARP request stores the sender’s (I, P) pair in its cache Send own table during the boot process (but may be too old) Entries in ARP cache should time out after some time (few minutes) 11. Mar. 2004 7 INF-3190: Internet

Address Resolution Protocol (ARP) n n End system not directly available by broadcast Example: ES 1 to ES 4 n ARP would not receive a response n n Solution 1: proxy ARP n the local router knows all remote networks with their respective routers n n n Ethernet broadcast is not rerouted over a router responds to local ARP local ES 1 sends data for ES 4 always to the local router, this router forwards the data (by interpreting the IP address contained in the data) Solution 2: remote network address is known n n local ES 1 sends data to the appropriate remote router local router forwards packets 11. Mar. 2004 8 INF-3190: Internet

Reverse Address Resolution Protocol (RARP) n Retrieve Internet address from knowledge of hardware address H H @IP: unknown @HW: 0 xaa H H H RARP Request source @IP: @HW: 0 xaa n RARP server responds n RARP server has to be available on the LAN n Application: diskless workstation boots over the network target @IP: 9. 228. 50. 3 @HW: 0 xa 3 e @HW: 0 xaa RARP Response source @IP: 9. 228. 50. 3 @HW: 0 xa 3 e target @IP: 9. 228. 50. 8 @HW: 0 xaa 11. Mar. 2004 9 INF-3190: Internet

Dynamic Host Configuration Protocol (DHCP) n DHCP has largely replaced RARP (and BOOTP) n n DHCP n n server answers DHCP server is used for assignment n n simplifies installation and configuration of end systems allows for manual and automatic IP address assignment may provide additional configuration information (DNS server, netmask, default router, etc. ) Client broadcasts DHCP DISCOVER packet n n extends functionality request can be relayed by DHCP relay agent, if server on other LAN Address is assigned for limited time only n n before the ’lease’ expires, client must renew it allows to reclaim addresses of disappearing hosts 11. Mar. 2004 10 INF-3190: Internet

IP Routing 11. Mar. 2004 11 INF-3190: Internet

IP Routing: Internal and External Routing n Direct Routing/ Interior Protocols: n n n N 0 Both source and destination ES are located in the same subnetwork source ES sends datagram to the destination ES identification done by the local address mapping routing is completely defined by the subnetwork routing algorithm N 1 N 2 N 4 N 5 N 3 Indirect Routing/Exterior Protocols: n Source and destination ES are located on different networks n n n source ES sends datagram to the next router each router determines the next router on the path to the destination ES routing decision is based only on n 11. Mar. 2004 the netid part of the Internet address, i. e. hostid is not used 12 INF-3190: Internet

IP Routing n Routing tables Networ k 10. 0 20. 0. 0. 5 40. 0. 0. 7 30. 0. 0. 6 Networ k k k F G H 20. 0. 0. 30. 0. 0. 40. 0 0 0 10. 0. 0. 5 30. 0. 0. 7 20. 0. 0. 6 Routing table of G n To reach host Route to this on network address 20. 0 Deliver direct 30. 0 Deliver direct 10. 0 20. 0. 0. 5 40. 0 30. 0. 0. 7 Routers may have incomplete information Default paths 11. Mar. 2004 13 INF-3190: Internet

IP Routing: Initial Gateway-to-Gateway Protocol (GGP) Original implementation ARPANET G 1 Local net 1 n … Local net 2 Gn Local net n Core Gateways n n n connect LANs to the backbone, know the routes to all networks exchange routing information with each other Gateway-to-Gateway Protocol (GGP): n n n G 2 distributed routing definition (group "Distance-Vector-Procedure") metrics: simply by distance Problems: particularly poor scalability n n n several backbones not all networks are connected directly to the backbone all Gateways communicate with each other 11. Mar. 2004 14 INF-3190: Internet

IP Routing: Autonomous Systems n Hidden networks Core gateways AS boundary router G 1 Local net 1 G 2 Local net 2 n Autonomous System G 3 Local net 3 G 4 Local net 4 Core gateways have to be informed about hidden networks Autonomous systems (AS) § Internet domains 11. Mar. 2004 15 INF-3190: Internet

IP Routing: Autonomous Systems n Types of ASs n Stub domains n n G 1 Autonomous system interconnect domain Gi G 2 Autonomous system … Gn Autonomous systems are administrative entities n n Collects routing information on networks in the AS Defines boundary routers (also called Exterior Gateways) n n No through traffic Transit domains n n source & sink only Multiconnected domain n n Core gateways that transmit routing information to other autonomous sys. Boundary routers n n Transmits information about network reachability only into its own AS Reason: each AS shall control exactly, to whom the information about reachability is given to 11. Mar. 2004 16 INF-3190: Internet

Interior Gateway Protocol IGPx Autonomous System x IGPx n n EGP n n n Other variants n individual solutions possible n e. g. HELLO by Dave Mills distributed routing algorithm n Routing Information Protocol (RIP), old Open Shortest Path First (OSPF) Interior Gateway Routing Protocol (IGRP) and Enhanced IGRP (EIGRP) 11. Mar. 2004 Autonomous System 1 IGP 1 Presently preferred procedures n G 1 Gx In general: intradomain routing n IGP 1 n 17 distance: Delay requires synchronized clocks INF-3190: Internet

Routing Information Protocol (RIP) n Background (regarding the originally used protocol) n n n Principle n n developed as a part of Berkeley UNIX since 1988, RIP Version 1, RFC 1058 i. e. n Distributed routing algorithm: Distance-Vector-Procedure IS periodically sends a list containing estimated distances to each destination to its neighbors n distance n n periodical n n number of hops: 0. . 15 (15 corresponds to infinite) every 30 sec; after 180 sek without packet distance infinite RIP Version 2 n G. Malkin, RFC 1387, 1388 and 1389 (RIP-MIB) n n n Uses multicast if necessary to distribute data Not broadcast (so that all ES also receive this) Networks without broadcast or multicast (ISDN, ATM) n n 11. Mar. 2004 “Triggered" updates To be sent only if the routing table changes 18 INF-3190: Internet

Open Shortest Path First (OSPF) n Background: since 1990 Internet Standard, RFCs 1247, 2178 n n Transition from vector-distance to link-state-protocol Principle (link-state-protocol) n IS measures "distance" to the immediately adjacent IS, distributes the information, calculates the optimal route n n determine the address of adjacent IS measure the "distance" (delay, . . ) to adjacent IS n n OSPF permits differing metrics selection per packet possible (RFC 1349) OSPF no. 0 2 4 8 16 n n n 11. Mar. 2004 Meaning Normal service Minimize financial cost Maximize reliability Maximize throughput Minimize delay process local link-state information as a packet distribute information to all adjacent IS by flooding compute route from the information of all IS e. g. with Dijkstra’s "shortest path first" algorithm name "Open Shortest Path First“ 19 INF-3190: Internet

Open Shortest Path First (OSPF) n n For large autonomous systems AS substructure n n To other AS AS AS backbone area Area Router classes n n AS boundary routers Backbone routers Area border routers Internal routers 11. Mar. 2004 To other AS 20 INF-3190: Internet

Open Shortest Path First (OSPF) n Adjacency n n LSR measures distance to all neighbours OSPF measures distance to all adjacent nodes If several routers are connected by a LAN n n One is designated router All other routers on the LAN are adjacent only to it It is adjacent to all others H H D E B A C D G I F transform to graph E B A C G I F F LAN N LAN are represented as star configurations 11. Mar. 2004 21 INF-3190: Internet

Exterior Gateway Protocol: Circumstances n Requirements, basic conditions n n n Core gateways political economical security-related AS 1 n Requirement examples n n n to avoid certain autonomous systems to avoid certain countries to stay within one country (before going via foreign country) data of company A should not to pass through company B AS 3 IG 1 AS 2 NW IG 2 Exchange information on accessibility n n including at least one Core Gateway possibly with other AS 11. Mar. 2004 23 INF-3190: Internet

Exterior Gateway Protocol Border Gateway Protocol (BGP) n Previously: Internet Exterior Gateway Protocol (RFC 1654) Now: Border Gateway Protocol (RFC 1771, 1772, 1773) is de-facto standard n Configurations n n n Possibility to have several Exterior Gateways per AS Variations n Branch (topology): n n Multiconnected networks n n networks with increased capacity and often linked to many AS Demands n To allow for routing path decisions n n n linked to many end systems can pass on traffic if necessary Transit networks n n all of the external traffic is routed over this/a single, external router e. g. to prefer to send traffic via own country e. g. not to send traffic through certain companies Routing policy can not only be based on a "minimal distance" 11. Mar. 2004 24 INF-3190: Internet

Exterior Gateway Protocol Border Gateway Protocol (BGP) n Algorithm n Fundamentals: based on distance vector mechanism, where n IS sends periodically to its neighbours a list containing n n the estimated distances from itself to all known destinations BGP uses distance path mechanism n Related to distance vector n n IS sends periodically a list to its neighbours containing n n But without count-to-infinity problem estimated distance and preferred Path from itself to each destination for a specified block of reachable IP addresses Receiving IS evaluates path n n Distance Policy compliance notion of a path / of how to reach other routers is distributed but, no criteria for selecting a route is distributed n each BGP router must have its own criteria, i. e. policy n n e. g. never send using certain AS Remarks n n Big updates But only a limited number of routers 11. Mar. 2004 25 INF-3190: Internet

Protocol Support in an IP Router BGP Network layer protocols n IP (Internet Protocol) ARP (Address Resolution Protocol), RARP (Reverse ARP) ICMP (Internet Control Message Protocol) IGMP (Internet Group Management Protocol) n n n ICMP IGMP RIP TCP SNMP UDP EGP OSPF IP ARP RARP SNAP LLC-1 n Routing protocols n n n RIP (Routing Information Protocol) BGP (Border Gateway Protocol) EGP (Exterior Gateway Protocol) OSPF (Open Shortest Path First) n Transport protocols n n Network management protocols n and n n 11. Mar. 2004 26 SNMP (Simple Network Management Protocol) UDP (User Datagram Protocol) TCP (Transmission Control Protocol) SNAP (Subnet Access Point) LLC (Logical Link Control) INF-3190: Internet