Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 1 Lesson 7 Internet Protocol (IP) Routing

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 2 Internet Protocol (IP) Routing Introduction to IP routing Types of links IP routing table Route determination process Sending host forwarding process IP router forwarding process Destination host receiving process IP routing infrastructure overview

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 3 Introduction to IP Routing Process of forwarding unicast IP traffic to its destination From the sending host through a series of intermediate routers The sending host and each router make a forwarding decision based on the contents of their local IP routing table Definitions: Node: a network device running the TCP/IP protocol Host: a TCP/IP node that does not have routing capability Router (or gateway): a TCP/IP node that does have routing capability

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 4 Direct and Indirect Delivery Router Host B Direct Delivery Indirect Delivery Host A Host C Direct Delivery

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 5 Types of Links Broadcast More than two nodes on the same network segment, and each frame sent is received at the Network Interface Layer by all of the network segment’s nodes Point-to-Point Only two nodes on the network segment Non-Broadcast Multiple Access (NBMA) Supports more than two IP nodes; however, no ability to multicast or broadcast

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 6 Broadcast Link Host A Host B Host D Host C Data flow Ethernet

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 7 Point-to-Point Link Router A Router B T1 leased line IP internetwork IP internetwork Data flow

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 8 NBMA Link Frame Relay cloud Site 1 Site 2 Site 3 Site 4 Router A Router B Router C Router D Separate virtual circuits Data flow

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 9 IP Routing Table Database of routes present in memory on all IP nodes Each route contains forwarding information for a range of destination addresses Used to determine, for each packet forwarded: The next-hop interface  Representation of a physical or logical device over which the IP datagram is forwarded The next-hop IP address  The IP address of the node to which the IP datagram is forwarded

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 10 Routing Table Structure Destination Network Mask Next-Hop IP Address Interface Metric To match a route: IP Address AND Network Mask = Destination

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 11 Types of Routes Host Route Routing on a per-IP address basis Network Mask of Network ID route Routing for a range of addresses (subnet, summarized address space) Default Route Destination of , Network Mask Used when no other more specific route matches the packet’s destination

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 12 Route Determination Process To choose a single route: Find the list of matching routes  Packet destination AND Network Mask = Destination Select longest (closest) matching route(s)  Most number of bits set to 1 in the Network Mask If more than one, choose longest matching route with lowest Metric If more than one, randomly choose among them Route Matching Preference 1. Host route 2. Subnet route 3. Class-based network route 4. Supernet or summarized route 5. Default route

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 13 Windows IP Routing Table F:\>route print ========================================================================== Interface List 0x MS TCP Loopback interface 0x a 56 0f 5b Linksys LNE100TX Fast Ethernet Adapter(LNE100TX v4) #2 ========================================================================== Active Routes: Network Destination Netmask Gateway Interface Metric Default Gateway: ========================================================================== Persistent Routes: None

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 14 Windows Route Determination Process 1. Perform the route determination process to choose a single route that is the closest match to the destination and has the lowest metric 2. From the chosen route, examine the gateway and interface IP addresses 3. If the gateway IP address is the same as the interface IP address, set the next-hop IP address to the destination IP address in the IP datagram being forwarded 4. If the gateway IP address is not the same as the interface IP address, set the next-hop IP address to the gateway IP address

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 15 Sending Host Forwarding Process The destination IP address is passed to the IP routing process, which determines the next-hop interface and IP address IP passes the IP datagram, the next-hop IP address, and the next-hop interface to ARP ARP resolves the next-hop IP address to a unicast MAC address for the indicated interface For a direct delivery, ARP resolves the destination’s MAC address For an indirect delivery, ARP resolves the intermediate router’s MAC address

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 16 IP Router Forwarding Process IP performs validation checks Checksum, Version, Source Routing IP checks the destination IP address in the IP datagram If the destination IP address in the datagram is a unicast address that is not a local host IP address, IP decrements the TTL value in the IP header If TTL > 0, update the checksum and perform the route determination process Pass next-hop address and interface to ARP

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 17 Destination Host Receiving Process IP performs validation checks Checksum, Version IP verifies that destination address is a local host address IP checks the Protocol field IP passes IP payload to upper layer protocol corresponding to the Protocol field

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 18 IP Routing Infrastructure Overview Single-path vs. multipath Class-based vs. classless Flat vs. hierarchical Static vs. dynamic Single vs. multiple autonomous systems

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 19 Routing Loops 0/0 Router A Router B Router C Router D 0/0

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 20 Hierarchical Addressing and Routing / / / / / / /19

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 21 Static vs. Dynamic Static routing relies on manually configured routes Dynamic routers rely on routing protocols to automatically maintain IP routing tables Routing Information Protocol (RIP)  Distance vector routing protocol Open Shortest Path First (OSPF)  Link stat routing protocol

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 22 OSPF Areas Backbone Area Area 1 Subnetted networks of /16 Summarized Route: /16 Area 2 Router A Router B

Microsoft Windows Server 2003 TCP/IP Protocols and Services Technical Reference Slide: 23 Review Introduction to IP routing Types of links IP routing table Route determination process Sending host forwarding process IP router forwarding process Destination host receiving process IP routing infrastructure overview