Static Routing
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The document discusses static routing and key concepts related to router configuration and operation. It defines static routes as manually configured paths that specify how a router will transmit packets to certain networks. The summary describes how to configure static routes, default routes, and route summarization. It also outlines tools for troubleshooting routing issues like missing routes.
![Summary and Default 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.
-Like route summarization this will help reduce the
size of the routing table
Configuring a default static route
Similar to configuring a static route. Except that destination IP
address and subnet mask are all zeros
Example:
-Router(config)#ip route 0.0.0.0 0.0.0.0 [exitinterface | ip-address ]
ITE 1 Chapter 6
© 2006 Cisco Systems, Inc. All rights reserved.
Cisco Public
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Static Routing
- 1. Static Routing Routing Protocols and Concepts – Lecture 7a ITE I Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 1
- 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 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 2
- 3. General Role 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, Router-to-Server, Hub-to-PC, Hub-to-Server Cross-over used to connect: -Switch-to-Switch, PC-to-PC, Switch-to-Hub, Hubto-Hub, Router-to-Router ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 3
- 4. Interfaces Examining Router Interfaces -Show IP router 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 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 4
- 5. Interfaces Configuring an Ethernet interface -By default all serial and Ethernet interfaces are down -To enable an interface use the No Shutdown command ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 5
- 6. Interfaces Configuring a Serial interface -Enter interface configuration mode -Enter in the ip address and subnet mask -Enter in the no shut down command Example: -R1(config)#interface serial 0/0 -R1(config-if)#ip address 172.16.2.1 255.255.255.0 -R1(config-if)#no shutdown -R1(config-if)#clockrate 56000 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 6
- 7. Routing Table and CDP Protocol 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 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 7
- 8. Routing Table and CDP Protocol ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 8
- 9. Routing Table and CDP Protocol 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 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 9
- 10. Routing Table and CDP Protocol Disabling CDP To disable CDP globally use the following command Router(config)#no cdp run Note : Enabled CDP can pose a security risk ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 10
- 11. Static Routes with Exit Interfaces Purpose A manually configured route used when routing from a network to a stub network ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 11
- 12. Static Routes with Exit Interfaces IP route command To configure a static route use the following command: ip route Example: -Router(config)# ip route network-address subnetmask {ip-address | exit-interface } ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 12
- 13. Static Routes with Exit Interfaces Dissecting static route syntax ip route - Static route command 172.16.1.0 - Network address of remote network 255.255.255.0 - Subnet mask of remote network 172.16.2.2 - Serial 0/0/0 interface IP address on R2, which is the "next-hop" to this network ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 13
- 14. Static Routes with Exit Interfaces Configuring routes to 2 or more remote networks Use the following commands for R1 -R1(config)#ip route 172.16.1.0 255.255.255.0 172.16.2.2 -R1(config)#ip route 192.168.2.0 255.255.255.0 172.16.2.2 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 14
- 15. Static Routes with Exit Interfaces Zinin’s 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." ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 15
- 16. Static Routes with Exit Interfaces Using Zinin’s 3 routing principles, how would you answer the following? -Would packets from PC1 reach their destination? Yes, packets destined for 172.16.1.0/24 and 192.168.2.0/24 networks would reach their destination. -Does this mean that any packets from these networks destined for 172.16.3.0/24 network will reach their destination? No, because neither R2 nor R3 router has a route to the 172.16.3.0/24 network. ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 16
- 17. Static Routes with Exit Interfaces Resolving to an Exit Interface -Recursive route lookup - Occurs when the router has to perform multiple lookups in the routing table before forwarding a packet. A static route that forwards all packets to the next-hop IP address goes through the following process (recursive route lookup) 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 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 17
- 18. Static Routes with Exit Interfaces Configuring a Static route with an Exit Interface -Static routes configured with an exit interface are more efficient because the routing -Table can resolve the exit interface in a single search instead of 2 searches -Example of syntax required to configure a static route with an exit interface -R1(config)#ip route 172.16.1.0 255.255.255.0 s/0/0/0 -R1(config)#ip route 192.168.2.0 255.255.255.0 s0/0/0 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 18
- 19. Static Routes with Exit Interfaces – graphic2.5.3.1 Verifying the Static Route Configuration -Use the following commands Step 1 show running-config Step 2 verify static route has been entered correctly Step 3 show ip route Step 4 verify route was configured in routing table Step 5 issue ping command to verify packets can reach destination and that Return path is working ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 19
- 20. Summary and Default 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. ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 20
- 21. Summary and Default Route Configuring a summary route Step 1: Delete the current static route Step 2: Configure the summary static route Step 3: Verify the new static route A summary route represent all the common bits for each network from left to right The 3 networks have 22 common bits from left to right ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 21
- 22. Summary and Default 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. -Like route summarization this will help reduce the size of the routing table Configuring a default static route Similar to configuring a static route. Except that destination IP address and subnet mask are all zeros Example: -Router(config)#ip route 0.0.0.0 0.0.0.0 [exitinterface | ip-address ] ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 22
- 23. Static Routes and Packet Forwarding Packet forwarding with static routes. (recall Zinin’s 3 routing principles) For Router 1. A static route that forwards all packets to the next-hop IP address goes through the following process (recursive route lookup) 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 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 23
- 24. Static Routes and Packet Forwarding 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 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 24
- 25. Static Routes and Packet Forwarding Solving a Missing Route ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 25
- 26. Static Routes and Packet Forwarding Solving a Missing Route ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 26
- 27. Summary Routers -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 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 27
- 28. Summary Static Routes -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 ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 28