CIS 632 / EEC 687 Mobile Computing

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Cuthbert Berry
6 years ago
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1 CIS 63 / EEC 687 Mobile Computing IP Software: Routing Prof. Chansu Yu Network Protocols for Wired Network: Ethernet Ethernet address 48-bit, also called hardware/physical/mac/layer address Globally unique: IEEE manages the assignment (give a block of addresses to manufacturers who do not know of locations of their installments) Thus, it does not tell the geographic location of the host Ethernet packet format P D P S

2 Network Protocols for Wired Network: IP (Internet Protocol) IP address 3-bit: IANA manages the assignment (give a block of addresses to institutions whose geographic location is fixed) Thus, it does tell the geographic location of the host 3 * IANA: Internet Assigned Numbers Authority Network Protocols for Wired Network: IP IP addresses are classful E.g. IP address of a CSU host : class B CSU netid 7.x.x.x = 0 xx..xx class A with netid of But it is used as a loopback address for TCP/IP testing Netid or hostid = 0 means this Netid or hostid = means all (broadcast, e.g., ) 4

3 How to deliver packets? Network Node (A) wants to send packets to (B) Packets must go though 4 different network domains and routers Q, R and S A Why do routers have IP addresses? Does A have to know B s IP address ( )? Does A have to know B s Ethernet address? Does A have to know S s IP address/ethernet address? Does A have to know Q s IP address/ethernet address? B Router R has three IP addresses. How does it forward packets from node A to the correct network ( ) instead of network? 5 How to deliver packets? Network Node (A) wants to send packets to (B) Packets must go though 4 different network domains and routers Q, R and S A S must know B s Ethernet address => ARP R must know that S is the next-hop router for the network => Routing table Q must know that R is the next-hop router for the network => Routing table B 6 3

4 Network Protocols for Wired Network: IP - Routing (I A, I B ) (I A, I B ) (I A, I B ) (P A, P R ) (P R, P B ) 7 Network Protocols for Wired Network: ARP (Address Resolution Protocol) ARP Every host listens to the Ethernet shared medium and check its destination address (physical address) with its own when one arrives Host A wants to communicate with host B Host A knows host B s IP address (I B ) but does not know his physical address (P B ), which is needed when sending over the Ethernet How does host A map I B to P B? 8 4

5 Network Protocols for Wired Network: ARP ARP solves the problem Each host has ARP cache to remember what he found ARP cache entry has timeout value (0 minutes) because a host can disappear or replace its Ethernet card 9 ARP Packet Encapsulation and Packet Format 0 5

6 Network Protocols for Wired Network: IP - Routing Router has more than one IP addresses. How about physical address? Network Protocols for Wired Network: IP Routing Table Lookup Network Prefix Host. If there is a host specific route that exactly matches the destination, then use this route. If there is a network-prefix route that matches the network-prefix portion of the packet s destination, use it : Pick the longest matching prefix 3. If there is a default route, pick it 4. Else send an unreachable message to the source (ICMP) 6

7 Network Protocols for Wired Network: IP Routing Table Lookup Longest matching entry 3 Network Protocols for Wired Network: IP Software 4 7

8 IP Packet Encapsulation and Packet Format 5 Packet arrives at the destination, then: Packet Demultiplexing Multiple network applications are running simultaneously on a host For example, one UDP application and two TCP applications (ftp and IE) A host receives a packet Should it pass to IP or ARP software? It it is IP, should it pass to UDP or TCP software? If it is TCP, should it pass to ftp or IE application? 6 8

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11 Network Protocols for Wired Network: Software Network Protocols for Wired Network: ICMP (Internet Control and Management Protocol) ICMP Routers send error/control messages to other routers/hosts Communication between protocol software (rather than communication between hosts) ICMP message types Echo request Else send an unreachable Echo reply message to the source (ICMP) Source quench Destination unreachable Redirect

12 ICMP Packet Encapsulation and Packet Format (each type has diff format) 3 Network Protocols for Wired Network: IP: Classless Network Address One network id for each physical network So many network id s are needed Solution : Proxy ARP Solution : Subnet 4

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14 IP Software: Routing 7 IP Software: Routing Routing algorithms Distance Vector (DV) Algorithm Link State (LS) Algorithm Reactive Proactive 8 4

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16 IP: Routing Packet-switched fixed (wired) network Packets are stored and forwarded (store-and-forward) toward destinations Key issues Routing : static (topology) and dynamic (traffic) factors Congestion control Error control Adaptive routing Isolated adaptive Centralized adaptive Distributed adaptive : Distance vector or Link state 3 IP: Routing () To get Cost Via B C 5 D E??? F??? A Node of interest 5 D B C E F 3 6

17 IP: Routing (3) To get Cost Via B C 5 D E??? F??? A 5 B 3 D C E F To get Cost Via A B C 3 E F??? 33 IP: Routing (4) To get Cost Via B C 4 D D E D F??? A 5 B 3 D C E F To get Cost Via A B C 3 E F??? 34 7

18 IP: Routing (5) To get Cost Via B C 4 D D E D F 4 D A 5 B 3 D 3 Each neighbor gives information (periodically) with the costs to all other nodes C 5 F E Distance vector at A = (, 4,,, 4) Next node vector at A = (B, D, D, D, D) 35 Distance vector algorithm IP: Routing (6) Distance vector algorithm (Bellman-Ford) Each node periodically broadcasts to its neighbors with the costs to all other nodes Cost is measured by hop count or delay ARPANET (969): 8ms period No knowledge of complete topology but simpler 36 8

19 IP: Routing (7) To get Cost Via B C 4 D D A 5 B 3 D 3 All other nodes gives information (periodically) with the costs to their neighbors C 5 E F 37 Link state algorithm IP: Routing (8) Link state algorithm (Dijkstra) Each node periodically broadcasts to all other nodes with the costs to its neighbors Cost is measured by queue length New ARPANET (979): 0s period Complete knowledge of total topology but much overhead Each node Computes the shortest path to all other nodes Knows the overall topology? 38 9

Homework 3 Discussion

Homework 3 Discussion Address Resolution Protocol (ARP) Data Link Layer Network Layer Data Link Layer Network Layer Protocol Data Unit(PDU) Frames Packets Typical Device Switch/Bridge Router Range Local