3 Static Routing.pptx

NETWORKING 2 NET102 Introduction ► Routing is at the core of every data network, moving information across an internetwork from source to destination. ► Routers are the devices responsible for the transfer of packets from one network to the next. ► Routers learn about remote networks e...

NETWORKING 2 NET102 Introduction ► Routing is at the core of every data network, moving information across an internetwork from source to destination. ► Routers are the devices responsible for the transfer of packets from one network to the next. ► Routers learn about remote networks either dynamically, using routing protocols, or manually, or using static routes. ► In many cases, routers use a combination of both dynamic routing protocols and static routes. Static Routing ► Static routes are common and do not require the same amount of processing and overhead as dynamic routing protocols. ► To reach remote networks, it is essential that routing be implemented. ► Routing can be accomplished dynamically using a routing protocol or manually using static routes. ► Very small organizations with a few remote networks would most likely use only static routes. ► However, larger networks typically use a combination of a dynamic routing protocol and static routes. Reaching Remote Networks ► Manually—Remote networks are manually entered into the route table using static routes. ► Dynamically—Remote routes are automatically learned using a dynamic routing protocol. ► Figure 2.1 provides a sample scenario of static routing. Reaching Remote Network ► Figure 2-2 provides a sample scenario of dynamic routing using Enhanced Interior Gateway Routing Protocol (EIGRP). Why Use Static Routing? ► Static routing provides some advantages over dynamic routing: ► Static routes are not advertised over the network, resulting in better security. ► Static routes use less bandwidth than dynamic routing protocols; no CPU cycles are used to calculate and communicate routes. ► The path a static route uses to send data is known ► Static routing has the following disadvantages: ► Initial configuration and maintenance is time consuming. ► Configuration is error-prone, especially in large networks. ► Administrator intervention is required to maintain changing route information ► It does not scale well with growing networks; maintenance becomes cumbersome. ► It requires complete knowledge of the whole network for proper implementation Dynamic vs Static Routing ► Static routes are useful for smaller networks with only one path to an outside network. ► They also provide security in a larger network for certain types of traffic or links to other networks that need more control. ►. It is important to understand that static and dynamic routing are not mutually exclusive. ► Rather, most networks use a combination of dynamic routing protocols and static routes. ► This may result in the router having multiple paths to a destination network via static routes and dynamically learned routes. ► However, recall that the administrative distance (AD) value is a measure of the preference of route sources. Dynamic vs Static Routing ► Route sources with low AD values are preferred over route sources with higher AD values. ► The AD value for a static route is 1. ► Therefore, a static route will take precedence over all dynamically learned routes, which will have higher AD values. When to use static routes ► Static routing has three primary uses: ► Providing ease of routing table maintenance in smaller networks that are not expected to grow significantly. ► Routing to and from stub networks. A stub network is a network accessed by a single route, and the router has only one neighbor. ► Using a single default route to represent a path to any network that does not have a more specific match with another route in the routing table. ► Default routes are used to send traffic to any destination beyond the next upstream router. Stub network ► In the figure, a static route can be configured on R2 to reach the R1 LAN. ► Additionally, because R1 has only one way to send out nonlocal traffic, a default static route can be configured on R1 to point to R2 as the next hop for all other networks. Static Route Application ► Static routes are most often used for the following reasons: ► Connect to a specific network ► Connect a stub router ► Summarize routing table entries ► Create a backup route ► They can also be used to do the following: ► Reduce the number of routes advertised by summarizing several contiguous networks as one static route ► Create a backup route in case a primary route link fails Types of IPv4 and IPv6 static routes ► Standard static route ► Default static route ► Summary static route ► Floating static route Standard Static Route ► Both IPv4 and IPv6 support the configuration of static routes. ► Static routes are useful when connecting to a specific remote network. ► Figure 2-4 shows that R2 can be configured with a static route to reach the stub network 172.16.3.0/24. Default Static Route ► A default route is one that matches all packets and is used by the router if a packet does not match any other, more specific route in the routing table. ► A default route can be dynamically learned or statically configured ► A default static route is simply a static route with 0.0.0.0/0 as the destination IPv4 address. ► Configuring a default static route creates a Gateway of Last Resort. ► Default static routes are used in two situations: ► When no other routes in the routing table match the packet destination IP address. In other words, when a more specific match does not exist. A common use is when connecting a company’s edge router to the ISP network ► When a router has only one other router to which it is connected. In this situation, the router is known as a stub router. Summary Static Route ► To reduce the number of routing table entries, multiple static routes can be summarized into a single static route in the following circumstances: ► The destination networks are contiguous and can be summarized into a single network address. ► All the multiple static routes use the same exit interface or next- hop IP address. Floating Static Route ► Floating static routes are static routes that are used to provide a backup path to a primary static or dynamic route, in the event of a link failure. ► The floating static route is only used when the primary route is not available. ► To accomplish this, the floating static route is configured with a higher AD than the primary route.