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Static Routing and Serial interfaces

Learn about static routing implementation, configuration of static and default routes, advantages/disadvantages of static routing, usage scenarios, and different types of static routes-focusing on IPv4 addresses. Static routes are manually created by network administrators to ensure secure and efficient network connectivity. Manually configure static routes, review CIDR, and troubleshoot common static route issues.

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Static Routing and Serial interfaces

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  1. Static Routing and Serial interfaces 2nd semester 1437-138

  2. Outline • Static Routing Implementation • Configure Static and Default Routes • Review of CIDR • Configure Summary and Floating Static Routes • Troubleshoot Static and Default Route Issues • Summary

  3. Static RoutingReach Remote Networks A router can learn about remote networks in one of two ways: • Manually - Remote networks are manually entered into the route table using static routes. • Dynamically - Remote networks are automatically learned using a dynamic routing protocol.

  4. Static RoutingStatic route • A static route is created, maintained, and updated by a network administrator, manually. • A static route to every network must be configured on every router for full connectivity.

  5. Static RoutingWhy Use Static Routing? Static routing provides some advantages over dynamic routing, including: • Static routes are not advertised over the network, resulting in better security. • Routers not share static routes with each other, thus reducing CPU/RAM overhead and saving bandwidth.

  6. Static RoutingWhy Use Static Routing? (continued) 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. • Does not scale well with growing networks; maintenance becomes cumbersome. • Requires complete knowledge of the whole network for proper implementation.

  7. Static RoutingWhen to Use Static Routes Static routing has three primary uses: • Small networks:Providing ease of routing table maintenance in smaller networks that are not expected to grow significantly. • Default route: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.

  8. Static RoutingWhen to Use Static Routes • Routing to and from stub networks. A stub network is a network accessed by a single route, and the router has no other neighbors (only one router).

  9. Static RoutingActivity - Identify the Advantages and Disadvantages of Static Routing

  10. Types of Static RoutesStatic Route Applications Static Routes are often used to: • Connect to a specific network • Provide a Gateway of Last Resort for a stub network • Summarize routing table entries • Create a backup route in case a primary route link fails

  11. Types of Static RoutesStandard Static Route Static route can be used to connect to a specific network ( like for example a stub network)

  12. Types of Static RoutesDefault Static Route • Static route can be used to configure default route. • A default static route is a route that matches all packets. • A default route identifies the gateway IP address to which the router sends all IP packets that it does not have a learned or static route. • 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.

  13. Types of Static RoutesDefault Static Route • Default static routes are used: • When no other routes in the routing table match the packet destination IP address. • When a router has only one other router to which it is connected. This condition is known as a stub router.

  14. Types of Static RoutesSummary Static Route

  15. Types of Static RoutesSummary Static Route To reduce the number of routing table entries, multiple static routes can be summarized into a single static route if: • The destination networks are contiguous and can be summarized into a single network address. • The multiple static routes all use the same exit interface or next-hop IP address.

  16. Types of Static RoutesFloating 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. • In order to accomplishthis, the floating static route is configured with a higher administrative distance than the primaryroute.

  17. Types of Static RoutesActivity - Identify the Type of Static Route

  18. Configure IPv4 Static Routesip route Command Next hop

  19. Configure IPv4 Static RoutesNext-Hop Options The next hop can be identified by an IP address, exit interface, or both. How the destination is specified creates one of the three following route types: • When only the next-hop IP address is specified  Next-hop static route. • When only the router exit interface is specified  Directly connected static route. • When the next-hop IP address and exit interface are specified  Fully specified static route.

  20. Configure IPv4 Static RoutesConfigure a Next-Hop Static Route

  21. Configure IPv4 Static RoutesConfigure a Next-Hop Static Route • In a next-hop static route, only the next-hop IP address is specified. • The output interface is derived from the next hop. • The router performs multiple lookups in the routing table before forwarding a packet( a recursive lookup). • Because recursive lookups consume router resources, they should be avoided when possible.

  22. Configure IPv4 Static RoutesConfigure Directly Connected Static Route When configuring a static route, another option is to use the exit interface to specify the next-hop address.

  23. Configure IPv4 Static RoutesConfigure Directly Connected Static Route • Configuring a directly connected static route with an exit interface allows the routing table to resolve the exit interface in a single search, instead of two searches. • Although the routing table entry indicates “directly connected”, the administrative distance of the static route is still 1. Only a directly connected interface can have an administrative distance of 0. • Note: For point-to-point interfaces, you can use static routes that point to the exit interface or to the next-hop address. For multipoint/broadcast interfaces, it is more suitable to use static routes that point to a next-hop address.

  24. Configure IPv4 Static RoutesConfigure a Fully Specified Static Route • In a fully specified static route, both the output interface and the next-hop IP address are specified. • This is another type of static route that is used in older IOS’s, prior to CEF. • This form of static route is used when the output interface is a multi-access interface and it is necessary to explicitly identify the next hop. • The next hop must be directly connected to the specified exit interface.

  25. Configure IPv4 Static RoutesConfigure a Fully Specified Static Route

  26. Configure IPv4 Static RoutesVerify a Static Route Along with ping and traceroute, useful commands to verify static routes include: • show ip route • show ip route static • show ip route network

  27. Configure IPv4 Static RoutesVerify a Static Route

  28. Configure IPv4 Default RoutesDefault Static Route

  29. Configure IPv4 Default RoutesConfigure a Default Static Route

  30. Configure IPv4 Default RoutesVerify a Default Static Route Note the asterisk (*)next to the route with code ‘S’. The asterisk indicates that this static route is a candidate default route, which is selected as the Gateway of Last Resort.

  31. Classful AddressingClassful Network Addressing and Default Subnet Masks Class AClass B Class C

  32. CIDRClassless Inter-Domain Routing Classful Addressing Waste 6.3.1.4

  33. CIDRCIDR and Route Summarization

  34. CIDRStatic Routing CIDR Example

  35. Configure IPv4 Summary RoutesCalculate a Summary Route

  36. Configure IPv4 Summary RoutesRoute Summarization • CIDR is a form of route summarization and is synonymous with the term supernetting. • CIDR ignores the limitation of classful boundaries, and allows summarization with masks that are smaller than that of the default classful mask. • This type of summarization helps reduce the number of entries in routing updates and lowers the number of entries in local routing tables.

  37. Configure IPv4 Summary RoutesSummary Static Route Example

  38. Types of Static RoutesActivity - Determine the Summary Network Address and Prefix

  39. Configure Floating Static RoutesFloating Static Routes • Floating static routes are static routes that have an administrative distance greater than the administrative distance of another static route or dynamic routes. • The administrative distance of a static route can be increased to make the route less desirable than that of another static route or a route learned through a dynamic routing protocol. • In this way, the static route “floats” and is not used when the route with the better administrative distance is active. • However, if the preferred route is lost, the floating static route can take over, and traffic can be sent through this alternate route.

  40. Configure Floating Static RoutesConfigure a Floating Static Route Default static route Floating default static route

  41. Configure Floating Static RoutesTest the Floating Static Route • Use a show ip route command to verify that the routing table is using the default static route. • Use a traceroute command to follow the traffic flow out the primary route. • Disconnect the primary link or shutdown the primary exit interface. • Use a show ip route command to verify that the routing table is using the floating static route. • Use a traceroute command to follow the traffic flow out the backup route.

  42. Troubleshoot IPv4 Static and Default Route ConfigurationTroubleshoot a Missing Route Common IOS troubleshooting commands include: • ping • traceroute • show ip route • show ip interface brief • show cdp neighbors detail 6.5.2.1

  43. Summary • Static routes can be configured with a next-hop IP address, which is commonly the IP address of the next-hop router. • When a next-hop IP address is used, the routing table process must resolve this address to an exit interface. • On point-to-point serial links, it is usually more efficient to configure the static route with an exit interface. • On multi-access networks, such as Ethernet, both a next-hop IP address and an exit interface can be configured on the static route. • Static routes have a default administrative distance of "1".

  44. Summary (continued) • A static route is only entered in the routing table if the next-hop IP address can be resolved through an exit interface. • Whether the static route is configured with a next-hop IP address or exit interface, if the exit interface that is used to forward that packet is not in the routing table, the static route is not included in the routing table. • In many cases, several static routes can be configured as a single summary route. • If there is not a more specific match in the routing table, the routing table uses the default route to forward the packet to another router. • A floating static route can be configured to back up a main link by manipulating its administrative value.

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