Giáo trình CCNA - Chương 3

CCNA – Semester3 Module 1 Introduction to Classless Routing Objectives • Define VLSM and devide major network with VLSM • Configure VLSM • Differences between RIPv1 and RIPv2 • Configure RIPv2 VLSM Why VLSM? • The addressing crisis • Rapid increase in the size of routing tables • IP address solutions: – Short term extensions to IPv4 – Subnetting 1985 – Variable length subnetting 1987 – Classless Interdomain Routing 1993 – Private IP address – Network Address Translation(NAT) –IPv6 What is VLSM? • With Variable-Length Subnet Masks (VLSM), a network administrator can use a long mask on networks with few hosts, and a short mask on subnets with many hosts • In order to use VLSM, a network administrator must use a routing protocol that supports it: –OSPF –IS-IS – EIGRP –RIPv2 –BGP – Static routing VLSM A waste of space • It has become acceptable practice to use the first and last subnets in a subnetted network in conjunction with VLSM. • With ip subnet-zero command, network has 8 usable subnets. Subnetting with VLSM Using VLSM VLSM Practice Subnet the network address 192.168.1.0/24 192.168.1.0/26 192.168.1.64/27 192.168.1.96/28 192.168.112.0/28 1 9 2 . 1 6 8 . 1 . 1 2 8 / 3 0 1 9 2 . 1 6 8 . 1 . 1 3 2 / 3 0 1 9 2 . 1 6 8 . 1 3 6 . 0 / 3 0 Route aggregation with VLSM • When using VLSM, try to keep the subnetwork numbers grouped together in the network to allow for aggregation. • The use of Classless InterDomain Routing (CIDR) and VLSM not only prevents address waste, but also promotes route aggregation, or summarization. Route Summarization Route Summarization Route Summarization (Super network) Route Summarization Rules • A router must know in detail the subnet numbers attached to it. • A router does not need to tell other routers about each individual subnet if the router can send one aggregate route for a set of routers. • A router using aggregate routes would have fewer entries in its routing table. RIP version 2 RIPv1 Limitations • It does not send subnet mask information in its updates. • It sends updates as broadcasts on 255.255.255.255. • It does not support authentication. • It is not able to support VLSM or classless interdomain routing (CIDR). RIPv2 • RIP v2 is an improved version of RIP v1 and shares the following features: – It is a distance vector protocol that uses a hop count metric. – It uses holddown timers to prevent routing loops – default is 180 seconds. – It uses split horizon to prevent routing loops. – It uses 16 hops as a metric for infinite distance. RIPv2 vs. RIPv1 Configuring RIP v2 • The router command starts the routing process. The network command causes the implementation of the following three functions: – The routing updates are multicast out an interface. – The routing updates are processed if they enter that same interface. – The subnet that is directly connected to that interface is advertised. [...]... link-state database afadjfjorqpoeru 39 547 439 0707 13 Hello afadjfjorqpoeru 39 547 439 0707 13 DBD afadjfjorqpoeru 39 547 439 0707 13 DBD Here is a summary of my link-state database Discovering Routes DR E0 172.16.5.1 E0 172.16.5 .3 afadjfjorqpoeru 39 547 439 0707 13 afadjfjorqpoeru 39 547 439 0707 13 LSAck Thanks for the information! LSAck Discovering Routes DR E0 172.16.5.1 E0 172.16.5 .3 afadjfjorqpoeru 39 547 439 0707 13. .. afadjfjorqpoeru 39 547 439 0707 13 LSAck Thanks for the information! LSAck Loading State afadjfjorqpoeru 39 547 439 0707 13 LSR I need the complete entry for network 172.16.6.0/24 afadjfjorqpoeru 39 547 439 0707 13 Here is the entry for network 172.16.6.0/24 afadjfjorqpoeru 39 547 439 0707 13 LSAck Thanks for the information! LSU Discovering Routes DR E0 172.16.5.1 E0 172.16.5 .3 afadjfjorqpoeru 39 547 439 0707 13 afadjfjorqpoeru 39 547 439 0707 13. .. List 172.16.5.2/24, int E0 Two-Way State Discovering Routes DR E0 172.16.5 .3 E0 172.16.5.1 Exstart State afadjfjorqpoeru 39 547 439 0707 13 Hello I will start exchange because I have router ID 172.16.5.1 No, I will start exchange because I have a higher router ID afadjfjorqpoeru 39 547 439 0707 13 Hello Discovering Routes DR E0 172.16.5 .3 E0 172.16.5.1 afadjfjorqpoeru 39 547 439 0707 13 Hello Exstart State I will... 39 547 439 0707 13 afadjfjorqpoeru 39 547 439 0707 13 LSAck Thanks for the information! LSAck Loading State afadjfjorqpoeru 39 547 439 0707 13 LSR I need the complete entry for network 172.16.6.0/24 afadjfjorqpoeru 39 547 439 0707 13 Here is the entry for network 172.16.6.0/24 LSU afadjfjorqpoeru 39 547 439 0707 13 LSAck Thanks for the information! Full State Maintaining Routing Information Link-State Change DR x 1 LSU A B •... neighbors, link-state information is exchanged OSPF network types • • A neighbor relationship, adjacent, is required for OSPF routers to share routing information which depends on network type OSPF interfaces recognize three types of networks: – Broadcast multi-access, such as Ethernet – Point-to-point networks – Nonbroadcast multi-access (NBMA), such as Frame Relay • A fourth type, point-tomultipoint,... n routers, n*(n-1)/2 adjacencies need to be formed • The solution to this overhead is to hold an election for a designated router (DR) • All routers in a network form adjacency with DR and BDR (backup designated router) • Link-state information sent to OSDF routers (DROther) at 224.0.0.5 • DROther sent link-state information to DR and BDR at 224.0.0.6 OSPF Network Type • On point-to-point networks... to ensure that neighbor routers are still functioning • Hellos are sent every 10 seconds by default on broadcast multi-access and point-to-point networks • On interfaces that connect to NBMA networks, such as Frame Relay, the default time is 30 seconds OPSF Packet Header • On multi-access networks the Hello protocol elects a designated router (DR) and a backup designated router (BDR) OSPF Hello Header... changes – Send triggered updates only when a network change has occurred – Send periodic updates known as link-state refreshes – Use a hello mechanism to determine the reachability of neighbors Link State Routing Link-state routing concepts • Link-state routing uses the following features: – Link-state advertisements (LSAs) – A topological database – The shortest path first (SPF) algorithm – The resulting... Link-State Change DR x 1 LSU A B • Router A tells all OSPF DRs on 224.0.0.6 Maintaining Routing Information 2 Link-State Change DR LSU x B A • DR tells others on 224.0.0.5 Maintaining Routing Information Link-State Change 2 DR x A B 3 LSU Maintaining Routing Information LSU LSA Is entry in link-state database? Is seq # the same? Yes No No Add to database Send LSAck to DR Yes Is seq # higher? No Run SPF... Vector Routing Link-state routing protocol • Collect routing information from all other routers in the network or within a defined area of the network • Each router independently calculates its best paths to all destinations in the network • It is less likely to propagate incorrect information provided by any of its neighboring routers Link-state routing protocol functions • Link-state routing protocols . CCNA – Semester3 Module 1 Introduction to Classless Routing Objectives • Define VLSM and devide major. Rapid increase in the size of routing tables • IP address solutions: – Short term extensions to IPv4 – Subnetting 1985 – Variable length subnetting 1987 – Classless Interdomain Routing 1993 – Private