Cisco IOS

Allocating External Addresses Dynamically Problem You want to dynamically select addresses from a pool. Solution You can configure the router to automatically select global addresses from a pool as they are required:Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#access-list ... [full story]

AutoQoS Problem You want the router to automatically generate the Quality of Service policy map for either VoIP or general IP traffic. Solution There are two versions of AutoQoS. The first is specific to VoIP traffic: Router1#configure terminal Enter configuration commands, one per line. End ... [full story]

Disabling Link Up/Down Traps per Interface Problem You want to disable link up/down traps for specific interfaces. Solution To disable SNMP link-status change traps for a particular interface, use the following configuration command: Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#interface ... [full story]

Disabling OSPF on Certain Interfaces Problem You want to prevent the some of a router's interfaces from taking part in OSPF. Solution The passive-interface configuration command effectively disables OSPF on an interface by preventing it from forming OSPF adjacencies: Router3#configure terminal Enter configuration commands, one ... [full story]

Foreign Agent Configuration Problem You want to configure a Foreign Agent router for IP Mobility to support one or more roaming Mobile Nodes. Solution Here is a minimal configuration for a Foreign Agent to support Mobile Nodes:RouterForeign#configure terminal Enter configuration commands, one per line. ... [full story]

Manual RSVP Reservations Problem You want to manually reserve bandwidth through your network to support a real-time application that isn't able to dynamically create new reservations as required. Solution In this example, we will assume that we have a host device, acting as the ... [full story]

Adjusting EIGRP Metrics Problem You want to modify the routing metrics for routes learned via EIGRP. Solution You can use the offset-list configuration command to modify the metrics of routes that EIGRP learns through a particular interface: Router1#configure terminal Enter configuration commands, one per ... [full story]

Adjusting for Daylight Saving Time Problem You want the router to automatically adjust to Daylight Saving Time. Solution Some areas, such as most of North America and Europe, have consistent and common rules for when to switch between winter or Standard time and ... [full story]

Adjusting LMI Options Problem You want to configure different LMI options on your Frame Relay circuit. Solution There are several different LMI options. The first specifies which version of LMI protocol you wish to use: Branch1#configure terminal Enter configuration commands, one per line. End with ... [full story]

Adjusting NAT Timers Problem You want to change the length of time that NAT entries remain active. Solution The router will keep NAT entries in the translation table for a configurable length of time. For TCP connections, the default timeout period is 86,400 seconds, ... [full story]

Adjusting OSPF Costs Problem You want to change the OSPF link costs. Solution The auto-cost reference-bandwidth command allows you to change the reference bandwidth that OSPF uses to calculate its metrics: Router5#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router5(config)#router ospf 87 Router5(config-router)#auto-cost ... [full story]

Adjusting OSPF Timers Problem You want to change the default OSPF timers to improve stability or convergence behavior. Solution You can improve the convergence time of OSPF on a particular interface by reducing the hello and dead timers: Router1#configure terminal Enter configuration commands, one ... [full story]

Adjusting the Next-Hop Attribute Problem You want to change the next-hop attribute on routes while distributing them via iBGP so that the routes always point to a next-hop address that is inside your AS. Solution By default, the value of the next-hop attribute for ... [full story]

Adjusting Timers Problem You wish to tune your EIGRP timers to improve network convergence. Solution There are two important EIGRP timers, the hello interval and the hold time. You can adjust both of these timers separately on each interface on a router as ... [full story]

Adjusting Timers Problem You wish to tune your routing protocol performance to improve the time that the network takes to converge after a topology change. Solution RIP has several timers that control things like how often it sends updates and how long it ... [full story]

Problem You want to edit an existing ACL directly on the router itself. Solution You can insert a single entry into an existing ACL by specifying a sequence number, as follows:Router2#configure terminal ... [full story]

Aggregating RSVP Reservations Problem You want to aggregate several RSVP reservations so that the core of your network doesn't need to keep track of them all separately. Solution This feature requires the creation of a boundary between the edge region of the network, where ... [full story]

Allocating External Addresses Statically Problem You want to translate specific internal IP addresses to specific external addresses. Solution For some applications, you need each internal (inside local) address to always translate to the same external (inside global) address. This is particularly true if you ... [full story]

Allocating Static IP Addresses with DHCP Problem You want to ensure that your router assigns the same IP address to a particular device every time it connects. Solution The following commands ensure that the router assigns the same IP address to a device each ... [full story]

Analyzing ACL Log Entries Problem You want to analyze the log entries created by logging ACLs. Solution The Perl script in Example 19-1 parses a router syslog file and builds a detailed report of packets that were denied by logging ACLs. By default, the ... [full story]

Applying Offsets to Routes Problem You want to modify the routing metrics for routes learned from or sent out through a particular interface. Solution You can modify the RIP metrics for a list of routes learned through a particular interface with the offset-list ... [full story]

Assured Forwarding DSCP values Drop Precedence Class 1 Class 2 Class 3 Class 4           Value Name Value Name Value Name Value Name Lowest Drop Precedence 001010(10) AF11 010010(18) AF21 011010(26) AF31 100010(34) AF41 Medium Drop Precedence 001100(12) AF12 010100(20) AF22 011100(28) AF32 100100(36) AF42 Highest Drop Precedence 001110(14) AF13 010110(22) AF23 011110(30) AF33 100110(38) AF43 For Expedited Forwarding there is only one value. It has a binary value of 101110, or 46 in decimal, and it is usually simply called ... [full story]

Authenticating BGP Peers Problem You want to authenticate your BGP peer relationships to help prevent tampering with your routing tables. Solution The BGP protocol includes an MD5-based authentication system for authenticating peers: Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router1(config)#router bgp ... [full story]

Authenticating Login IDs from a Central System Problem You want to administer login ID and password information centrally for all routers. Solution Cisco changed the AAA syntax slightly in Version 12.0(5)T. The following set of commands allows you to configure TACACS+ authentication in the ... [full story]

Authentication Proxy Problem You want the router to separately authenticate and authorize individual users as they access restricted resources. Solution To enable an IOS-based authentication proxy, use the following commands:Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router1(config)#aaa ... [full story]

Auto Tuning Buffers Problem You want the router to automatically tune the buffers, based on computed needs of the router. Solution Use the buffers tune automatic command to enable the router to auto tune the system buffers: Router#configure terminal Enter configuration commands, one per line. ... [full story]

Automatically Generating IPv6 Addresses for an Interface Problem You want to enable IPv6 and generate addresses automatically. Solution There are two methods for generating IPv6 addresses automatically. The first uses the autoconfig command:Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router1(config)#ipv6 unicast-routing ... [full story]

Automating Dial Backup Problem You want automatic dial recovery in case a WAN link fails. Solution One of the most reliable ways of implementing dial backup on a Cisco router is to use a floating static default route, as follows: Router1#configure terminal Enter configuration commands, ... [full story]

Automating the Login Sequence Problem You want to automate the process of logging into a router, typing usernames, passwords, and so forth. Solution The following script automates the process of logging into the router using a scripting language called Expect. Expect is a powerful ... [full story]

Backing Up Router Configurations Problem You need to download all of the active router configurations to see what has changed recently. Solution The Perl script in Example 1-4 automatically retrieves and stores router configuration files on a nightly basis. By default, it retains these ... [full story]

Booting a Different IOS Image Problem You want to boot using an alternate IOS image. Solution To specify which IOS image the router should load next time it reboots, use the boot system command: Router1#configure terminal Enter configuration commands, one per line. End with ... [full story]

Booting over the Network Problem You want to load an IOS image that is too large to store on your router's local flash. Solution You can load an IOS image that is larger than your router's flash by configuring the router to first use ... [full story]