Transcript Ch10
Chapter Overview Routing Principles Building Routing Tables 1 Routing Protocols Key to the network connection info Contract routing tables dynamically Costs are CPU time and network traffics IGP and EGP (Interior/Exterior gateway protocols) 2 Routing Basics 3 Administrative Distances (AD) It is use to rate the trustworthiness of routing info received on one router from its neighboring routers A number between 0 to 255 0 is the most trusted 255 == no traffic should go there Entering to routing table if two routers both can reach an IP Rule #1, go with a lower AD Rule #2, if the two ADs are the same, do hop count, etc cost/metrics calculations If cost/metrics calculations are all the same, do a “Load Balance” test by sending messages to the two routers 4 AD numbers 5 Three classes of routing protocols Distance vector Link State Router has 3 tables: (1) directly attached neighbors, (2) table used to determines the topology of the entire internetwork, (3) actual routing table It knows more about the network than Distance Vector It use an algorithm to calculate the shortest path Hybrid Count the number of routers (hops) between two points Combines the two, Cisco proprietary protocol No “best” approach 6 Dynamic Routing 7 Distance-Vector Routing Routing by rumor A router passes COMPLETE routing-table to neighboring routers The received routing table is combined with a router’s own routing table without verification Use hop count to determine routing, then AD, then “load balancing” Know the directly connected networks initially Build the tables afterward 8 Example, initial routing tables 9 Example, populated 10 RIP Characteristics RIP: the acronym for Routing Information Protocol Most common interior gateway protocol (IGP) in the TCP/IP suite Originally designed for UNIX systems as a daemon called routed Eventually ported to other platforms Standardized in Request for Comments (RFC) 1058 Updated to version 2, published as RFC 2453 11 RIP Communications RIP routers initiate communications when starting up by broadcasting a request message on all network interfaces. All RIP routers receiving the broadcast respond with reply messages containing their entire routing table. The router receiving the replies updates its own routing table with the information in the reply messages. 12 RIP Version 1 Message Format Refresh every 30 seconds 3 minutes == out Not support subnet mask Max hop count 15 – used by small networks only 13 RIP Version 2 Message Format Message are sent using UDP (user Datagram Protocol) Port 520 14 RIP 2 From http://www.tcpipguide.com/free/t_RIPVersion2RIP2MessageFormatandFeatures-3.htm 15 RIP vs. RIP v2 VLSM = Variable Length Subnet mask Discontiguous == two connecting subnets come from different classful network Such as connecting 172.16.16.1/24 with 10.3.1.1/24 16 Discontiguous 17 Interior Gateway Protocols (IGP) and Exterior Gateway Protocols (EGP) Border Gateway Protocol (BGP). IGP EGP 18 OSPF Protocol OSPF: the acronym for Open Shortest Path First (EGP/IGP) Standardized in RFC 2328 Uses link-state routing Offers several advantages: Updates routing tables more quickly when changes occur on the network Balances the network load by splitting traffic between routes with equal metrics Supports authentication of routing protocol messages 19 OSPF and RIPs 20 How powerful/useful OSPF is 21 IPv6 Routing Cannot broadcast RIPng <== RIPv2 EIGRPv6 EIGPR OSPFv3 OSPF 22 ? --cast 23