The IP Route Command
The command for configuring a static route is ip route. The complete syntax for configuring a static route is:
Router(config)#ip route prefix mask {ip-address | interface-type interface-number [ip-address]} [distance] [name] [permanent] [tag tag]
Most of these parameters are not relevant for this chapter or for your CCNA studies. As shown in the figure, we will use a simpler version of the syntax:
Router(config)#ip route network-address subnet-mask {ip-address | exit-interface }
The following parameters are used:
network-address - Destination network address of the remote network to be added to the routing table
subnet-mask - Subnet mask of the remote network to be added to the routing table. The subnet mask can be modified to summarize a group of networks.
One or both of the following parameters must also be used:
ip-address - Commonly referred to as the next-hop router's IP address
exit-interface - Outgoing interface that would be used in forwarding packets to the destination network
Note: The ip-address parameter is commonly referred to as the "next-hop" router's IP address. The actual next-hop router's IP address is commonly used for this parameter. However, the ip-address parameter could be any IP address, as long as it is resolvable in the routing table. This is beyond the scope of this course, but we've added this point to maintain technical accuracy.
The command for configuring a static route is ip route. The complete syntax for configuring a static route is:
Router(config)#ip route prefix mask {ip-address | interface-type interface-number [ip-address]} [distance] [name] [permanent] [tag tag]
Most of these parameters are not relevant for this chapter or for your CCNA studies. As shown in the figure, we will use a simpler version of the syntax:
Router(config)#ip route network-address subnet-mask {ip-address | exit-interface }
The following parameters are used:
network-address - Destination network address of the remote network to be added to the routing table
subnet-mask - Subnet mask of the remote network to be added to the routing table. The subnet mask can be modified to summarize a group of networks.
One or both of the following parameters must also be used:
ip-address - Commonly referred to as the next-hop router's IP address
exit-interface - Outgoing interface that would be used in forwarding packets to the destination network
Note: The ip-address parameter is commonly referred to as the "next-hop" router's IP address. The actual next-hop router's IP address is commonly used for this parameter. However, the ip-address parameter could be any IP address, as long as it is resolvable in the routing table. This is beyond the scope of this course, but we've added this point to maintain technical accuracy.
Purpose and Command Syntax of ip route
As we have discussed previously, a router can learn about remote networks in one of two ways:
Manually, from configured static routes
Automatically, from a dynamic routing protocol
The rest of this chapter focuses on configuring static routes. Dynamic routing protocols are introduced in the next chapter.
Static routes
Static routes are commonly used when routing from a network to a stub network. A stub network is a network accessed by a single route. For an example, see the figure. Here we see that any network attached to R1 would only have one way to reach other destinations, whether to networks attached to R2 or to destinations beyond R2. Therefore, network 172.16.3.0 is a stub network and R1 is a stub router.
Running a routing protocol between R1 and R2 is a waste of resources because R1 has only one way out for sending non-local traffic. Therefore, static routes are configured for connectivity to remote networks that are not directly connected to a router. Again, referring to the figure, we would configure a static route on R1 to the LAN attached to R2. We will also see how to configure a default static route from R1 to R2 later in the chapter so that R1 can send traffic to any destination beyond R2.
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Router Connections
Connecting a router to a network requires a router interface connector to be coupled with a cable connector. As you can see in the figure, Cisco routers support many different connector types.
Serial Connectors
Picture Router Connections
For WAN connections, Cisco routers support the EIA/TIA-232, EIA/TIA-449, V.35, X.21, and EIA/TIA-530 standards for serial connections, as shown. Memorizing these connection types is not important. Just know that a router has a DB-60 port that can support five different cabling standards. Because five different cable types are supported with this port, the port is sometimes called a five-in-one serial port. The other end of the serial cable is fitted with a connector that is appropriate to one of the five possible standards.
Note: The documentation for the device to which you want to connect should indicate the standard for that device.
Newer routers support the smart serial interface that allows for more data to be forwarded across fewer cable pins. The serial end of the smart serial cable is a 26-pin connector. It is much smaller than the DB-60 connector used to connect to a five-in-one serial port. These transition cables support the same five serial standards and are available in either DTE or DCE configurations.
Note: For a thorough explanation of DTE and DCE, see Lab 1.5.1, "Cabling a Network and Basic Router Configuration."
These cable designations are only important to you when configuring your lab equipment to simulate a "real-world" environment. In a production setting, the cable type is determined for you by the WAN service you are using.
Ethernet Connectors
A different connector is used in an Ethernet-based LAN environment. An RJ-45 connector for the unshielded twisted-pair (UTP) cable is the most common connector used to connect LAN interfaces. At each end of an RJ-45 cable, you should be able to see eight colored strips, or pins. An Ethernet cable uses pins 1, 2, 3, and 6 for transmitting and receiving data.
DTE SERIAL
DTE SMART SERIAL
Two types of cables can be used with Ethernet LAN interfaces:
A straight-through, or patch cable, with the order of the colored pins the same on each end of the cable
A crossover cable, with pin 1 connected to pin 3, and pin 2 connected to pin 6
Straight-through cables are used for:
Switch-to-router
Switch-to-PC
Hub-to-PC
Hub-to-server
Crossover cables are used for:
Switch-to-switch
PC-to-PC
Switch-to-hub
Hub-to-hub
Router-to-router
Router-to-server
Note: Wireless connectivity is discussed in another course.
Related Topic Router
Connecting a router to a network requires a router interface connector to be coupled with a cable connector. As you can see in the figure, Cisco routers support many different connector types.
Serial Connectors
Picture Router ConnectionsFor WAN connections, Cisco routers support the EIA/TIA-232, EIA/TIA-449, V.35, X.21, and EIA/TIA-530 standards for serial connections, as shown. Memorizing these connection types is not important. Just know that a router has a DB-60 port that can support five different cabling standards. Because five different cable types are supported with thi
s port, the port is sometimes called a five-in-one serial port. The other end of the serial cable is fitted with a connector that is appropriate to one of the five possible standards.Note: The documentation for the device to which you want to connect should indicate the standard for that device.
Newer routers support the smart serial interface that allows for more data to be forwarded across fewer cable pins. The serial end of the smart serial cable is a 26-pin connector. It is much smaller than the DB-60 connector used to connect to a five-in-one serial port. These transition cables support the same five serial standards and are available in either DTE or DCE configurations.
Note: For a thorough explanation of DTE and DCE, see Lab 1.5.1, "Cabling a Network and Basic Router Configuration."
These cable designations are only important to you when configuring your lab equipment to simulate a "real-world" environment. In a production setting, the cable type is determined for you by the WAN service you are using.
Ethernet Connectors
UTP CABLE
A different connector is used in an Ethernet-based LAN environment. An RJ-45 connector for the unshielded twisted-pair (UTP) cable is the most common connector used to connect LAN interfaces. At each end of an RJ-45 cable, you should be able to see eight colored strips, or pins. An Ethernet cable uses pins 1, 2, 3, and 6 for transmitting and receiving data.
DTE SERIALDTE SMART SERIALTwo types of cables can be used with Ethernet LAN interfaces:
A straight-through, or patch cable, with the order of the colored pins the same on each end of the cable
A crossover cable, with pin 1 connected to pin 3, and pin 2 connected to pin 6
Straight-through cables are used for:
Switch-to-router
Switch-to-PC
Hub-to-PC
Hub-to-server
Crossover cables are used for:
Switch-to-switch
PC-to-PC
Switch-to-hub
Hub-to-hub
Router-to-router
Router-to-server
Note: Wireless connectivity is discussed in another course.
Related Topic Router
- Dinamic Routing
- Static Routing
- Basic Routing Configuration
- Routing Tables Principles
- Router Interface
- Router Bootup
- Router And Network Layer
- Introducing Routing And Packet Forwading
- Route Filtering
- Dinamyc Routing Protocol
- Policy Routing
- Routing Issu
The router is a special-purpose computer that plays a key role in the operation of any data network. Routers are primarily responsible for interconnecting networks by:
Determining the best path to send packets
Forwarding packets toward their destination
Routers perform packet forwarding by learning about remote networks and maintaining routing information. The router is the junction or intersection that connects multiple IP networks. The routers primary forwarding decision is based on Layer 3 information, the destination IP address.
The router's routing table is used to find the best match between the destination IP of a packet and a network address in the routing table. The routing table will ultimately determine the exit interface to forward the packet and the router will encapsulate that packet in the appropriated data link frame for that outgoing interface.
Related Topic Router
Forwarding packets toward their destination
Routers perform packet forwarding by learning about remote networks and maintaining routing information. The router is the junction or intersection that connects multiple IP networks. The routers primary forwarding decision is based on Layer 3 information, the destination IP address.
Related Topic Router
Determining a router's best path involves the evaluation of multiple paths to the same destination network and selecting the optimum or "shortest" path to reach that network. Whenever multiple paths to reach the same network exist, each path uses a different exit interface on the router to reach that network. The best path is selected by a routing protocol based on the value or metric it uses to determine the distance to reach a network. Some routing protocols, such as RIP, use simple hop-count, which the number of routers between a router and the destination network. Other routing protocols, such as OSPF, determine the shortest path by examining the bandwidth of the links, and using the links with the fastest bandwidth from a router to the destination network.
Dynamic routing protocols typically use their own rules and metrics to build and update routing tables. A metric is the quantitative value used to measure the distance to a given route. The best path to a network is the path with the lowest metric. For example, a router will prefer a path that is 5 hops away over a path that is 10 hops away.
The primary objective of the routing protocol is to determine the best paths for each route to include in the routing table. The routing algorithm generates a value, or a metric, for each path through the network. Metrics can be based on either a single characteristic or several characteristics of a path. Some routing protocols can base route selection on multiple metrics, combining them into a single metric. The smaller the value of the metric, the better the path.
Comparing Hop Count and Bandwidth Metrics
Two metrics that are used by some dynamic routing protocols are:
Hop count-Hop count is the number of routers that a packet must travel through before reaching its destination. Each router is equal to one hop. A hop count of four indicates that a packet must pass through four routers to reach its destination. If multiple paths are available to a destination, the routing protocol, such as RIP, picks the path with the least number of hops.
Bandwidth-Bandwidth is the data capacity of a link, sometimes referred to as the speed of the link. For example, Cisco's implementation of the OSPF routing protocol uses bandwidth as its metric. The best path to a network is determined by the path with an accumulation of links that have the highest bandwidth values, or the fastest links. The use of bandwidth in OSPF will be explained in Chapter 11.
Note: Speed is technically not an accurate description of bandwidth because all bits travel at the same speed over the same physical medium. Bandwidth is more accurately defined as the number of bits that can be transmitted over a link per second.
When hop count is used as the metric, the resulting path may sometimes be suboptimal. For example, consider the network shown in the figure. If RIP is the routing protocol used by the three routers, then R1 will choose the suboptimal route through R3 to reach PC2 because this path has fewer hops. Bandwidth is not considered. However, if OSPF is used as the routing protocol, then R1 will choose the route based on bandwidth. Packets will be able to reach their destination sooner using the two, faster T1 links as compared to the single, slower 56 Kbps link.
Dynamic routing protocols typically use their own rules and metrics to build and update routing tables. A metric is the quantitative value used to measure the distance to a given route. The best path to a network is the path with the lowest metric. For example, a router will prefer a path that is 5 hops away over a path that is 10 hops away.
The primary objective of the routing protocol is to determine the best paths for each route to include in the routing table. The routing algorithm generates a value, or a metric, for each path through the network. Metrics can be based on either a single characteristic or several characteristics of a path. Some routing protocols can base route selection on multiple metrics, combining them into a single metric. The smaller the value of the metric, the better the path.
Comparing Hop Count and Bandwidth Metrics
Two metrics that are used by some dynamic routing protocols are:
Hop count-Hop count is the number of routers that a packet must travel through before reaching its destination. Each router is equal to one hop. A hop count of four indicates that a packet must pass through four routers to reach its destination. If multiple paths are available to a destination, the routing protocol, such as RIP, picks the path with the least number of hops.
Bandwidth-Bandwidth is the data capacity of a link, sometimes referred to as the speed of the link. For example, Cisco's implementation of the OSPF routing protocol uses bandwidth as its metric. The best path to a network is determined by the path with an accumulation of links that have the highest bandwidth values, or the fastest links. The use of bandwidth in OSPF will be explained in Chapter 11.
Note: Speed is technically not an accurate description of bandwidth because all bits travel at the same speed over the same physical medium. Bandwidth is more accurately defined as the number of bits that can be transmitted over a link per second.
When hop count is used as the metric, the resulting path may sometimes be suboptimal. For example, consider the network shown in the figure. If RIP is the routing protocol used by the three routers, then R1 will choose the suboptimal route through R3 to reach PC2 because this path has fewer hops. Bandwidth is not considered. However, if OSPF is used as the routing protocol, then R1 will choose the route based on bandwidth. Packets will be able to reach their destination sooner using the two, faster T1 links as compared to the single, slower 56 Kbps link.
