1. Routing Protocols and Concepts – Chapter 2
Static Routing
Routing Protocols and Concepts – Chapter 2

2. Objectives Define the general role a router plays in networks.
Describe the directly connected networks, different router interfaces
Examine directly connected networks in the routing table and use the CDP protocol
Describe static routes with exit interfaces
Describe summary and default route
Examine how packets get forwarded when using static routes
Identify how to manage and troubleshoot static routes

3. Context Index 2.1 Router and Network 2.2 Router Configuration Review
2.3 Exploring Directly Connected Networks
2.4 Static Route with “Next Hop” Address
2.5 Static Routes with Exit Interfaces
2.6 Summary and Default Static Routes
2.7 Managing and Troubleshooting Static Routes
2.8 Static Route Configuration Labs

4. 2.1 Router and Network
路由器和网络

5. 2.1.1 Role of the Router Functions of a Router Best Path Selections
Forwarding packets to destination

6. 2.1.2 Introducing the Topology
3 routers connected via WAN links
Each router connected to a LAN represented by a switch and a PC

7. 2.1.3 Examining the connection of the Router
Connections of a Router for WAN
-A router has a DB-60 port that can support 5 different cabling standards
Connections of a Router for Ethernet
-2 types of connectors can be used: Straight through and Cross-over
Straight through used to connect:
-Switch-to-Router, Switch-to-PC, Hub-to-PC, Hub-to-Server
Cross-over used to connect:
-Switch-to-Switch, PC-to-PC, Switch-to-Hub, Hub-to-Hub, Router-to-Router , Router-to-Server

8. 2.1.3 Examining the connection of the Router

9. 2.2 Router Configuration Review
路由器配置回顾

10. 2.2.1 Examining Router Interfaces
-Show ip route command – used to view routing table
-Show Interfaces command – used to show status of an interface
-Show ip Interface brief command – used to show a portion of the interface information
-Show running-config command – used to show configuration file in RAM

11. 2.2.1 Examining Router Interfaces
出厂配置时的显示：默认情况下，所有路由器接口都是 shutdown 状态（即已关闭）

12. 2.2.2 Configuring an Ethernet Interface
Unsolicited Messages from IOS

13. 2.2.2 Configuring an Ethernet Interface
Reading the Routing Table

14. 2.2.3 Verifying Ethernet interface

15. 2.2.3 Verifying Ethernet interface
Ethernet interfaces participate in ARP

16. 2.2.4 Configuring a Serial Interface
-Enter interface configuration mode
-Enter in the ip address and subnet mask
-Enter in the no shutdown command
Example:
R1(config)# interface serial 0/0/0
R1(config-if)# ip address
R1(config-if)# no shutdown

17. Physically connecting a WAN Interface
A WAN Physical Layer connection has sides:
Data Circuit-terminating Equipment (DCE) – This is the service provider. CSU/DSU is a DCE device.
Data Terminal Equipment (DTE) – Typically the router is the DTE device.

18. 2.2.5 Examining Router Interfaces
Configuring serial links in a lab environment
One side of a serial connection must be considered a DCE
This requires placing a clocking signal – use the clock rate command.
Example:
R1(config)# interface serial 0/0/0
R1(config-if)# clockrate 64000

19. 2.2.5 Examining Router Interfaces

20. 2.3 Exploring Directly Connected Networks
探究直连路由

21. 2.3.1 Verifying Changes the Routing Table
Routing Table Concepts
show ip route command reveals the content of the routing table.
Why only have one Connected Route?

22. 2.3.1 Verifying Changes the Routing Table
Observing Routes as They are Added to the Routing Table.

23. 2.3.1 Verifying Changes the Routing Table
Remove a Connected Route from Routing Table
Disable debug ip routing by using either the undebug ip routing command or the undebug all command.

24. 2.3.2 Devices on Directly Connected Networks
When a router only has its interfaces configured & no other routing protocols are configured then:
-The routing table contains only the directly connected networks
-Only devices on the directly connected networks are reachable

25. 2.3.2 Devices on Directly Connected Networks

26. 2.3.2 Devices on Directly Connected Networks
Pings are discarded

27. 2.3.3 Cisco Discovery Protocol (CDP)
Purpose of CDP
A layer 2 Cisco proprietary tool used to gather information about other directly connected Cisco devices.
Concept of neighbors
2 types of neighbors
Layer 3 neighbors
Layer 2 neighbors (CDP operates at Layer 2 only)

28. 2.3.3 Cisco Discovery Protocol (CDP)
CDP Operation (间隔60s，失效时间180s)
CDP show commands
Show cdp neighbors
Displays the following information:
Neighbor device ID
Local interface
Holdtime value, in seconds
Neighbor device capability code
Neighbor hardware platform
Neighbor remote port ID
Show cdp neighbors detail
-Useful in determining if an IP address configuration error

29. 2.3.4 Using CDP for Network Discovery

30. 2.4 Static Route with “Next Hop” Address
带下一跳地址的静态路由

31. 2.4.1 Purpose and Command Syntax of ip route
Purpose of ip route
A manually configured route used when routing from a network to a stub network

32. 2.4.1 Purpose and Command Syntax of ip route
IP route command
To configure a static route use the following command: ip route
Example:

33. 2.4.2 Configuring Static Route
Installing a Static Route in the Routing Table

34. 2.4.2 Configuring Static Route
Configuring routes to 2 or more remote networks
R1(config)# ip route
R1(config)# ip route

35. 2.4.3 Routing Table Principles and Static route
3 Routing principles
Principle 1: "Every router makes its decision alone, based on the information it has in its own routing table.“
Principle 2: "The fact that one router has certain information in its routing table does not mean that other routers have the same information.“
Principle 3: "Routing information about a path from one network to another does not provide routing information about the reverse, or return path."
Ping测试：
PC1 to
PC1 to
PC1 to PC2
PC3 to PC2

36. 2.4.3 Routing Table Principles and Static route
Finish the configuration
Finish the configuration

37. 2.4.4 Recursive Route Lookup
Resolving to an Exit Interface
The router first must match static route’s destination IP address with the Next hop address
The next hop address is then matched to an exit interface

38. 2.4.4 Recursive Route Lookup

39. 2.4.4 Recursive Route Lookup
Exit Interface is Down

40. 2.5 Static Routes with Exit Interfaces
带送出接口的静态路由

41. 2.5.1 Static Route and an Exit Interface
Configuring a Static route with an Exit Interface (本路由器接口)
single search instead of 2 searches.
serial point-to-point networks.

42. 2.5.2 Modifying Static routes
Existing static routes cannot be modified. The old static route must be deleted by placing no in front of the ip route
Example:
no ip route
A new static route must be rewritten in the configuration

43. 2.5.3 Verifying the Static Route Configuration
TEST
Try it

44. 2.5.4 Static routes and Ethernet exit interfaces
需要进行ARP解析
下一跳表示为接口时可能会出现问题

45. 2.6 Summary and Default Static Routes
总结和默认静态路由

46. 2.6.1 Summary Static Route
Summarizing routes reduces the size of the routing table.
Route summarization is the process of combining a number of static routes into a single static route.

47. 2.6.1 Summary Static Route Configuring a summary static route
Step 1: Delete the current static route
Step 2: Configure the summary static route
Step 3: Verify the new static route

48. 2.6.2 Default Static Route Default Static Route
This is a route that will match all packets.
Stub routers that have a number of static routes all exiting the same interface are good candidates for a default route.
Configuring a default static route
Example:
Router(config)# ip route [exit-interface | ip-address ]

49. R1(config)# ip route 0.0.0.0 0.0.0.0 serial 0/0/0
2.6.2 Default Static Route
Default static routes and subnet masks
Since the subnet mask used on a default static route is all packets will match.
R1(config)# ip route serial 0/0/0

50. Verifying a Default Static Route
Before

51. 2.7 Managing and Troubleshooting Static Routes
静态路由的管理和排错

52. 2.7.1 Static Routes and Packet Forwarding
The following is an example of the packet forwarding process with static routes. As you can see in the animation, PC1 is sending a packet to PC3:
1. The packet arrives on the FastEthernet 0/0 interface of R1.
2. R1 does not have a specific route to the destination network, /24; therefore, R1 uses the default static route.
3. R1 encapsulates the packet in a new frame. Because the link to R2 is a point-to-point link, R1 adds an "all 1s" address for the Layer 2 destination address.
4. The frame is forwarded out the serial 0/0/0 interface. The packet arrives on the Serial 0/0/0 interface on R2.

53. 2.7.1 Static Routes and Packet Forwarding
The following is an example of the packet forwarding process with static routes. As you can see in the animation, PC1 is sending a packet to PC3:
5. R2 decapsulates the frame and looks for a route to the destination. R2 has a static route to /24 out Serial0/0/1.
6. R2 encapsulates the packet in a new frame. Because the link to R3 is a point-to-point link, R2 adds an "all 1s" address for the Layer 2 destination address.
7. The frame is forwarded out the Serial0/0/1 interface. The packet arrives on the Serial0/0/1 interface on R3.
8. R3 decapsulates the frame and looks for a route to the destination. R3 has a connected route to /24 out FastEthernet 0/1.

54. 2.7.1 Static Routes and Packet Forwarding
The following is an example of the packet forwarding process with static routes. As you can see in the animation, PC1 is sending a packet to PC3:
9. R3 looks up the ARP table entry for to find the Layer 2 MAC address for PC3.
a. If no entry exists, R3 sends an ARP request out FastEthernet 0/0.
b. PC3 responds with an ARP reply which includes the PC3 MAC address.
10. R3 encapsulates the packet in a new frame with the MAC address of interface FastEthernet 0/0 as the source Layer 2 address and the MAC address of PC3 as the destination MAC address.
11. The frame is forwarded out the FastEthernet 0/0 interface. The packet arrives on the NIC interface of PC3.

55. 2.7.2 Troubleshooting a Missing Route
Tools that can be used to isolate routing problems include:
-Ping– tests end to end connectivity
-Traceroute– used to discover all of the hops (routers) along the path between 2 points
-Show ip route– used to display routing table & ascertain forwarding process
-Show ip interface brief– used to show status of router interfaces
-Show cdp neighbors detail– used to gather configuration information about directly connected neighbors

56. 2.7.3 Solving a Missing Route
Finding a missing or mis-configured route requires methodically using the correct tools.
-Start with PING. If ping fails then use traceroute to determine where packets are failing to arrive
Issue: show ip route to examine routing table.
-If there is a problem with a mis-configured static route remove the static route then reconfigure the new static route

57. 2.7.3 Solving a Missing Route
R2(config)#no ip route serial0/0/1
R2(config)#ip route serial 0/0/0
R2(config)# no ip route serial0/0/1
R2(config)# ip route serial 0/0/0

58. 2.8 Static Route Configuration Labs

59. Summary Routers Connecting Networks Cisco Discovery Protocol
-Operate at layer 3
-Functions include best path selection & forwarding packets
Connecting Networks
WANs
Serial cables are connected to router serial ports.
In the lab environment clock rates must be configured for DCE
LANs
Straight through cables or cross over cables are used to connect to fastethernet port. (The type of cable used depends on what devices are being connected)
Cisco Discovery Protocol
A layer 2 proprietary protocol
Used to discover information about directly connected Cisco devices

60. Summary Static Routes Summary static routes Default route
-This is a manually configured path that specifies how the router will get to a certain point using a certain path.
Summary static routes
-This is several static routes that have been condensed into a single static route.
Default route
-It is the route packets use if there is no other possible match for their destination in the routing table.
Forwarding of packets when static route are used
-Zinin’s 3 routing principles describe how packets are forwarded
Troubleshooting static routes may require some of the following commands:
-Ping
-Traceroute
-Show IP route
-Show ip interface brief
-Show cdp neighbors detail