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Introduction to IP Part II Neil Tang 10/27/2008

Introduction to IP Part II Neil Tang 10/27/2008. Overview. Datagram Forwarding ARP DHCP ICMP. Datagram Forwarding. In a router If (NetworkNum of destination = NetworkNum of one of interfaces) then forward packet to destination directly over that interface Else

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Introduction to IP Part II Neil Tang 10/27/2008

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  1. Introduction to IPPart IINeil Tang10/27/2008 CS440 Computer Networks

  2. Overview • Datagram Forwarding • ARP • DHCP • ICMP CS440 Computer Networks

  3. Datagram Forwarding In a router If (NetworkNum of destination = NetworkNum of one of interfaces) then forward packet to destination directly over that interface Else If (NetworkNum of destination is in my forwarding table) then forward the packet to the Nexthop router based on forwarding table Else forward the packet to the default router In a host If (NetworkNum of destination = my NetworkNum) then forward packet to the destination directly Else forward the packet to the default router CS440 Computer Networks

  4. Datagram Forwarding Forwarding Table in R2 A routing/forwarding table only lists a set of network numbers rather than all the nodes in those networks. CS440 Computer Networks

  5. Address Translation Protocol (ARP) • The ARP is used to obtain the corresponding physical address based on an IP address. • Each host maintains a table of IP-physical address pairs in the cache. • In ARP, a host broadcast an ARP query including the target IP address into the network. Each host receiving the query checks to see if it matches its IP address. If yes, the host sends a response message including its physical address. CS440 Computer Networks

  6. 0 8 16 31 Hardware type = 1 ProtocolType = 0x0800 HLen = 48 PLen = 32 Operation SourceHardwareAddr (bytes 0 ― 3) ― ― 5) 1) SourceHardwareAddr (bytes 4 SourceProtocolAddr (bytes 0 SourceProtocolAddr (bytes 2 TargetHardwareAddr (bytes 0 ― 3) ― 1) ― 5) TargetHardwareAddr (bytes 2 TargetProtocolAddr (bytes 0 ― 3) Address Translation Protocol (ARP) CS440 Computer Networks

  7. Dynamic Host Configuration Protocol (DHCP) • DHCP is usually used by a host to obtain configuration information such as IP address dynamically. • The information will be stored in the DHCP server and automatically retrieved by each host when it is booted or connected to the network. • DHCP allows addresses to be leased for some period of time. A host needs to renew it after timeout, otherwise the address will be returned to the pool. • With the DHCP, a network administrator can configure a range of IP addresses. In this way, network scalability is improved. CS440 Computer Networks

  8. Dynamic Host Configuration Protocol (DHCP) A host sends a DHCPDISCOVER message to the broadcast IP address (255.255.255.255). All other hosts will simply ignore this message but the DHCP server will reply it with requested information. Multiple networks may share a common DHCP server. There is at least one DHCP agent in each network, which is used to relay the DHCPDISCOVER messages to the server. CS440 Computer Networks

  9. Internet Control Message Protocol (ICMP) • ICMP defines a collection of error messages that will be sent back to the source host whenever a router or host is unable to process an IP datagram successfully. • The error messages include “destination unreachable”, “redirect”, “time exceed” and so on. CS440 Computer Networks

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