Dr. Clincy1 Chapter 6 Delivery & Forwarding of IP Packets Lecture #4 Items you should understand by now – before routing Physical Addressing – with in the local network Network Addressing and subnetting – across interconnected networks What is being routed across interconnected networks – IP Datagram – Frame purpose ? Access Methods versus Routing versus Switching ?? Go into Routing now Routing conceptually How routers work Routing Protocols versus Routing Algorithms Unicast Routing and Multicast Routing

Dr. Clincy2 ROUTING METHODS There are various routing methods: Next-Hop Routing – table only holds the address of the next hop (instead info regarding the entire route) – routing table for each host Network-Specific Routing – instead of an entry for each host (on the same network), only one entry for the network is defined Host-Specific Routing – for a specific destination host, you might want to control the exact route – in this case, the actual Rx is listed in the routing table and the desired next hop is listed Default Routing – instead of listing all of the various networks in the Internet, Tx host would use one entry called the Default (network address )

Dr. Clincy3 Next-hop routing Next-Hop Routing – table only holds the address of the next hop (instead info regarding the entire route) Show more routers in better illustrating the routing table

Dr. Clincy4 Network-specific routing Network-Specific Routing – instead of an entry for each host on the same physical network, only one entry for the network is defined

Dr. Clincy5 Host-specific Routing Host-Specific Routing – for a specific destination host, you might want to control the exact route – in this case, the actual Rx is listed in the routing table and the desired next hop is listed In this case, you want every packet traveling to Host B to traverse through R3. For the other hosts on N2 and N3, the Network-specific routing approach is used.

Dr. Clincy6 Default Routing Default Routing – instead of listing all of the various networks in the Internet, Tx host would use one entry called the Default (network address ) In this case, R1 sends to a specific network however, R2 sends to the remainder of the Internet (default)

Dr. Clincy7 Simplified forwarding module in classful address without subnetting For the Classful case, per router, a table was needed for each class – this made the searching simple

Dr. Clincy8 Configuration for routing for R1, Classful Case

Dr. Clincy9 Simplified forwarding module in classful address with subnetting Recall for the Classful case, subnetting is done within the organization

Dr. Clincy10 Configuration for the Classful and Subnetting Case Doesn’t know what network is connected to router here

Dr. Clincy11 Simplified forwarding module in classless address

Dr. Clincy12 Routing Table for R1 in the Illustrated Configuration – Classless Case

Dr. Clincy13 Address aggregation With the classless approach, routing tables increased – in reducing the size of some tables, use a router to represent multiple blocks – address aggregation

Dr. Clincy14 STATIC VERSUS DYNAMIC ROUTING Host or router uses a routing table Table can be either static or dynamic in nature A static routing table contains information entered manually. A dynamic routing table is updated periodically using one of the dynamic routing protocols such as RIP, OSPF, or BGP Regarding dynamic routing table: if fiber cut or router failure, the tables are updated

Dr. Clincy15 Router’s Table Logistics When the router is looking for the route, it: First check for direct delivery Then host-specific delivery, The network-specific delivery, and Finally, default delivery This order can be organized with in the routing table

Dr. Clincy16 Routing Table Flags U - The router is up and running. If router is down, the packet discarded G - The destination is in another network. If G flag present, indirect delivery (if not, direct delivery) H – If H flag present, destination field contains Host-specific address (if not present, network address) D – If D flag present, routing info added to host routing table via ICMP’s redirection (cover later) M - If M flag present, routing info was modified via ICMP’s redirection (cover later) Mask: used to extract the net id of the Rx. For Host-Specific Routing - the mask is and for Default Routing – the mask is Destination Address: either the destination host address or destination network address Next-hop Address: next hop router address Reference count: # of users using this route at any moment Use: # of packets transmitted through this router for the corresponding Rx Interface: name of the interface

Dr. Clincy17 A routing example Router R1 receives 500 packets for destination how does Router R1 uses it’s routing table ???

Dr. Clincy18 MaskDest.Next Hop I m m m m m m m0 Direct delivery &  no match &  no match U case UGH case UG case the router applies the masks to the destination address until a match with the second column

Dr. Clincy19 MaskDest.Next Hop I m m m m m m m0 Host-specific &  no match Network-specific &  match U case UGH case UG case Router stops when match is made

Dr. Clincy20 Example 2 Make the routing table for router R1 in the Figure MaskDestinationNext HopI m m m m0 U UG

Dr. Clincy21 STRUCTURE OF A ROUTER We represent a router as a black box that accepts incoming packets from one of the input ports (next hop), uses a routing table to find the departing output port, and sends the packet from this output port (interface). The topics discussed in this section include: Components

Dr. Clincy22 Router components Performs layer 1 and 2 functions: signal to bits, packet decapsulated from frame, error control performed on bits, buffers packets before going to the switching fabric Performs layer 1 and 2 functions: bits to signal, packet encapsulated into frame, error control overhead added This is where delay is incurred

Dr. Clincy23 Crossbar Switching Fabric Cross Point

Dr. Clincy24 A banyan switch Uses a binary string to route across the switch Example Given a packet came in on port 1 and needed to go out of port 6, the binary string of 110 will be used – explain this