Static Routing

• Static Routing


  Technique of manually defining routes to allow routers to forward packets to remote networks
• Static Routing


  • Security is inherent because routers do not transmit network topology information
  • No additional route computation (CPU), data structures (memory) or router control messages (network bandwidth) necessary
  • Routes explicitly configured by administrator, therefore network traffic path is predictable
• Static Routing


  • Does not scale well to large networks because of administrative overhead
  • Does not automatically respond to changes in network topology and traffic conditions
  • Configuration complexity increases as network size increases
• Static Routing Usage Scenarios

  • Smaller networks that are not expected to grow
  • As a default route forwarding packets to a service provider
  • For routing between stub networks (network with only one path to an outside network)
  • For routes outside the routing domain and not learned by the dynamic routing protocol
  • When the network administrator wants to explicitly define the path for a specific network
• Types of Static Routes


  • Standard Static Route
  • Summary Static Route
  • Default Static Route
  • Floating Static Route
• Standard Static Route


  Route where the route prefix identifies a specific destination network
• Summary Static Route


  Route that represents multiple routes as a single large network, often used to reduce the number of routes in the routing table
• Default Static Route


  Route used to match and route all packets that do not match a more specific route in the routing table, commonly used on stub routers or edge routers connected to the ISP network
• Floating Static Route


  Route used to provide a backup path that a router will use when a primary route is not available, configured by assigning a higher administrative distance than the main route
• IP Route Command


  1. ip route network-address subnet-mask {next_hop | exit_int [next_hop]} [admin_dist]

  2. ipv6 route ipv6-prefix/prefix-length {next_hop | exit_int [next_hop]} [admin_dist]
• Standard Static Route Configuration

  • Recursive route
  • Directly connected static route
  • Fully specified static route
• Summary Static Route Configuration

  1. Step 1: Set the subnet mask / prefix length to where the leftmost bits are common to all subnets

  2. Step 2: Retain the common bits

  3. Step 3: Zero out bits to the right of the new subnet mask / prefix length
• Default Static Route


  A static route that matches all packets and represents any network that is not in the routing table, often configured on edge or stub routers
• Configure Floating Static Routes

  Configure a static route with a higher administrative distance than the primary route so it is used only when the primary route is not available
• Verify Static Routes


  1. show ip route / show ipv6 route - shows all routes

  2. show ip route static / show ipv6 route static - shows static routes
• Default route


  Route used by packets that do not match any specific network routes in the routing table, characterized by an all-0 network address and mask
• Configuring static routes


  1. Define destination network

  2. Define next hop

  3. Define exit interface

  4. Define administrative distance
• Static routes


  • Manually configured routes suitable for small networks or as complement to dynamic routes
  • More secure, less resource utilization, predictable path
  • Not scalable to large networks, do not automatically respond to topology changes
• Standard static route


  Route to a single network
• Summary route


  Combines multiple contiguous subnets sharing the same exit interface from a router into a single route entry
• Floating route


  Backup route that will be used when a primary route fails, configured by setting the administrative distance higher than the primary route
• Troubleshooting static routes


  1. Verify Layer 3 connectivity with ping

  2. Verify path to destination with traceroute

  3. Verify routing table with show ip route

  4. Verify interface status with show ip interface brief

  5. Verify directly connected Cisco devices with show cdp neighbors
• Traceroute utility is useful for diagnosing routing issues
• Traceroute output


  • C:\WINDOWS\system32>tracert 192.168.2.2
  • Tracing route to 192.168.2.2 over a maximum of 30 hops
  • 1 2 ms 1 ms 1 ms 172.16.3.1
  • 2 3 ms 2 ms 4 ms 172.16.2.2
  • 3 5 ms 6 ms 4 ms 192.168.1.1
  • 4 5 ms 7 ms 7 ms 192.168.2.2
  • Trace complete.
• Missing or erroneous route

  Traceroute output shows route failing after 2nd hop
• Routing loop


  Traceroute output shows packet bouncing between 2 hops
• Routing table on R2 indicates wrong next hop address for 172.16.3.0/24 network
• Routing table on R2 indicates route to 192.168.2.0/24 has R1 as next hop, causing routing loop
• Static Routing


  Technique of manually defining routes to allow routers to forward packets to remote networks
• Static Routing


  • Security is inherent because routers do not transmit network topology information
  • No additional route computation (CPU), data structures (memory) or router control messages (network bandwidth) necessary
  • Routes explicitly configured by administrator, therefore network traffic path is predictable
• Static Routing


  • Does not scale well to large networks because of administrative overhead
  • Does not automatically respond to changes in network topology and traffic conditions
  • Configuration complexity increases as network size increases
• Static Routing Usage Scenarios

  • Smaller networks that are not expected to grow
  • As a default route forwarding packets to a service provider
  • For routing between stub networks (network with only one path to an outside network)
  • For routes outside the routing domain and not learned by the dynamic routing protocol
  • When the network administrator wants to explicitly define the path for a specific network
• Types of Static Routes

  • Standard Static Route
  • Summary Static Route
  • Default Static Route
  • Floating Static Route
• Standard Static Route


  Route where the route prefix identifies a specific destination network
• Summary Static Route


  Route that represents multiple routes as a single large network, often used to reduce the number of routes in the routing table
• Default Static Route


  Route used to match and route all packets that do not match a more specific route in the routing table, commonly used on stub routers or edge routers connected to the ISP network
• Floating Static Route


  Route used to provide a backup path that a router will use when a primary route is not available, configured by assigning a higher administrative distance than the main route
• IP Route Command


  1. ip route network-address subnet-mask {next_hop | exit_int [next_hop]} [admin_dist]

  2. ipv6 route ipv6-prefix/prefix-length {next_hop | exit_int [next_hop]} [admin_dist]
• Standard Static Route Configuration

  • Recursive route
  • Directly connected static route
  • Fully specified static route
• Summary Static Route Configuration

  1. Step 1: Set the subnet mask / prefix length to where the leftmost bits are common to all subnets

  2. Step 2: Retain the common bits

  3. Step 3: Zero out bits to the right of the new subnet mask / prefix length