Lecture (01) Determining IP Routes (1)

Transcription

1 Lecture (01) Determining IP Routes (1) By: Dr. Ahmed ElShafee ١ Dr. Ahmed ElShafee, ACU : Fall 2016, Practical App. Networks II Overview Routing is the process of determining where to send data packets destined for addresses outside the local network. Routers gather and maintain routing information to enable the transmission and receipt of such data packets. Conceptually, routing information takes the form of entries in a routing table, with one entry for each identified route. The network administrator can statically (manually) configure the entries in the routing table or the router can use a routing protocol to create and maintain the routing table dynamically to accommodate network changes whenever they occur. ٢

2 To effectively manage an IP network, you must understand the operation of both static and dynamic routing protocols and the impact that they have on an IP network. ٣ Router Operations Routing is the process by which an item gets from one location to another. In networking, a router is the device used to route traffic. ٤

3 To be able to route anything, a router, or any entity that performs routing, must do the following: Identify the destination address: Detennine the destination (or address) of the item that needs to be routed. Identify sources of routing information: Determine from which sources (other routers) the router can learn the paths to given destinations. ٥ Identify routes: Determine the initial possible routes, or paths, to the intended destination. Select routes: Select the best path to the intended destination. Maintain and verify routing information: Determine if the known paths to the destination are the most current. ٦

4 routing information that a router obtains from other routers is placed in its routing table router will rely on this table to tell it which interfaces to use when forwarding addressed packets ٧ If the destination network is directly connected, the router already knows which interface to use when forwarding packets. If destination networks are not directly attached, the router must learn the Dr. best Ahmed ElShafee, route ACU to : Fall us 2016, when Practical App. forwarding Networks II packets ٨

5 There are two ways in which the destination information can be learned. Routing information can be entered manually by the network administrator. Routing information can be collected through the dynamic routing process Dr. Ahmed that ElShafee, is running ACU : Fall 2016, in Practical the App. routers. Networks II ٩ Identifying Static and Dynamic Routes Static Route Uses a route that a network administrator enters into the router manually Dynamic Route Uses a route that a network routing protocol adjusts automatically for topology or traffic changes ١٠

6 Static: The router learns routes when an administrator manually configures the static route. The administrator must manually update this static route entry whenever an internetwork topology change requires an update. Static routes are user defined routes that specify the path that packets take when moving between a source and a destination. These administrator defined routes allow very precise control over the routing behavior of the IP internetwork. ١١ Dynamic: The router dynamically learns routes after an administrator configures a routing protocol that helps determine routes. Unlike the situation with static routes, after the network administrator enables dynamic routing, the routing process automatically updates route knowledge whenever new topology information is received. The router learns and maintains routes to the remote destinations by exchanging routing updates with other routers in the internetwork. ١٢

7 Static Routes Configure unidirectional static routes to and from a stub network to allow communications to occur ١٣ Static routes are commonly used when you are routing from a network to a stub network. A stub network (sometimes called a leaf node) is a network accessed by a single route. Static routes can also be useful for specifying a "gateway of last resort" to which all packets with an unknown destination address will be sent. ١٤

8 Example: Static Routes router A will be configured with a static route to reach the subnet via router A's serial interface. Router B will be configured with a static or default route to reach the networks behind router A via router B's serial interface. ١٥ Defines a path to an IP destination network or subnet or host: Router(config)#ip route network {address I interface}[distance] [mask] [permanent] enter the ip route command in global configuration mode. ip route Command Description network mask address interface ١٦ Parameters Destination network or subnetwork or host. Subnet mask IP address of the next hop router Name of the interface to use to get to the destination network. The interface should be a point to point interface. The command will not work properly if the interface is multiaccess (for example, a shared media Ethernet interface).

9 Router(config)#ip route network {address I interface}[distance] [mask] [permanent] ip route Command Description distance permanent Parameters (Optional) Defines the administrative distance. Administrative distance is covered in the Dynamic Routing Protocol topic. (Optional) Specifies that the route will not be removed, even if the interface shuts down ١٧ ١٨ Router(config)#ip route ip route Command Parameters ip route Description Identifies the static route command. Specifies a static route to the destination subnetwork. Indicates the subnet mask. (There are 8 bits of subnetting in effect.) IP address of the next hop router in the path to the destination.

10 Default Route Forwarding Configuration This route allows the stub network to reach all known ١٩ networks beyond router A. Use a default route in situations when the route from a source to a destination is not known or when it is not feasible for the router to maintain many routes in its routing table. ٢٠

11 Router(config ) #ip route ip route Command Parameters ip route ٢١ Description Identifies the static route command. Routes to nonexistent subnetworks. (With a special mask, this parameter denotes the default network.) Special mask indicating the default route. IP address of the next hop router to be used as the default for packet forwarding Static Route Configuration Verification look for static routes signified by "S." You should see a verification output as shown in the figure. The asterisk(*) indicates the last path used when a packet was ٢٢ forwarded.

12 Practical ٢٣ Step 1 router A ********* en config t interface fa0/0 ip address no sh exit interface serial0/1/0 ip address no sh clock rate exit interface loopback 0 ip address no sh end copy running config startup config ٢٤

13 router b ******** en config t interface fa0/0 ip address no sh exit interface serial0/1/0 ip address no sh exit interface loopback 0 ip address no sh end copy running config startup config ٢٥ PCS ******** PC1 ip: PC2 ip: GW: ٢٦

14 Step 02 Router A routing **************** enable conf t ip route ip route serial0/1/0 copy running config startup config ************ check step 2 ************ from router A >> ping from PC1 >> ping from router A >> show ip route ٢٧ step 3 Router B routing **************** enable conf t ip route ip route Serial0/1/0 copy running config startup config ************ check step 2 ************ from PC1 >> ping from PC1 >> ping from router A >> show ip route ٢٨

15 Step 4 Router A routing II **************** enable conf t ip route ip route Serial0/1/0 copy running config startup config ************ check step 4 ************ from PC1 >> ping from PC1 >> ping from router A >> show ip route ٢٩ Thanks,.. See you next week (ISA), ٣٠ Dr. Ahmed ElShafee, ACU : Fall 2016, Practical App. Networks II