Cisco IOS

Using HSRP Preempt Problem You want to ensure that a particular router is always selected as the "active" HSRP router, whenever it is up and functioning. Solution You can ensure that a particular router is always selected as the HSRP active router if it ... [full story]

Making HSRP React to Problems on Other Interfaces Problem You want HSRP to switch to the backup router when another port on the primary router becomes unavailable. Solution The standby track configuration command reduces the priority of an active HSRP router into a standby ... [full story]

Load-Balancing with HSRP Problem You want to load-balance your traffic between two (or more) HSRP routers. Solution You can configure HSRP so that both routers are always in use if they are available. This allows you to use your network resources more efficiently, but ... [full story]

Redirecting ICMP with HSRP Problem You want to enable ICMP redirects with HSRP. Solution In older IOS releases, when you enable HSRP on an interface, the router will automatically disable ICMP redirection. However, starting with IOS Version 12.1(3)T, Cisco has changed how ICMP redirection ... [full story]

Manipulating HSRP Timers Problem You want to decrease the amount of time it takes for the backup router to take over after the primary router fails. Solution You can configure HSRP-enabled routers to recover more quickly after the primary HRSP router becomes unavailable with ... [full story]

Using HSRP on Token Ring Problem You want to configure HSRP on a Token Ring. Solution You can use HSRP on a Token Ring LAN exactly the same as in Recipe 22.1 if the only protocol on the segment is IP. However, if you ... [full story]

HSRP SNMP Support Problem You want to enable HSRP SNMP traps. Solution Cisco has developed an HSRP SNMP MIB to help manage routers using this feature. You can configure your router to send an SNMP trap every time the routers make an HSRP state ... [full story]

Changing TCP Ports for FTP Problem You have an FTP server that uses a nonstandard TCP port number. Solution The FTP protocol includes IP address information in the packet payload. Normally, Cisco's NAT implementation rewrites IP address information in the payloads of FTP ... [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]

Stateful NAT Failover Problem You want to use NAT in a high availability configuration, allowing a second router to take over NAT functionality if the first fails. Solution Stateful NAT allows you to combine NAT functionality with HSRP using two routers in a high ... [full story]

Showing DHCP Status Problem You want to display the status of the DHCP server functions on the router. Solution To display the IP address bindings and their associated leases, use the following command:Router1#show ip dhcp binding The following command displays any IP address conflicts ... [full story]

Debugging DHCP Problem You want to debug a DHCP problem. Solution To debug the server events, use the following EXEC command:Router1#debug ip dhcp server events The following command will allow you to monitor the actual DHCP-related packets being transmitted and received by the router:Router1#debug ... [full story]

Configuring Basic NAT Functionality Problem You want to set up Network Address Translation on your router. Solution In the simplest NAT configuration, all of your internal devices use the same external global address as the router's external interface:Router#configure terminal Enter configuration commands, one per ... [full story]

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]

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]

Translating Some Addresses Statically and Others Dynamically Problem You want certain hosts to have static address translation properties and all others to use dynamic translation. Solution In some cases you might need to use a combination of the two approaches. Some internal devices will ... [full story]

Using Route Maps to Refine Static Translation Rules Problem You want to use route maps to give finer control over your static NAT translation rules. Solution One of the best uses of this feature appears when you have two Internet Provider connections and you ... [full story]

Translating in Both Directions Simultaneously Problem You want to translate both internal and external addresses. Solution In some cases, you might need to translate IP addresses on both sides of your router:Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#access-list ... [full story]

Rewriting the Network Prefix Problem You want to rewrite all of the addresses in a particular range by simply replacing the prefix with one of equal length. Solution Sometimes you need to connect your network to another network that uses an unregistered range, such ... [full story]

Using NAT for Server Load Distribution Problem You have several application servers and you want to use NAT so that users can connect to them by a single IP address, distributing the load across all of the servers. Solution The rotary keyword allows you ... [full story]

Increasing HSRP Security Problem You want to increase the Security of HSRP between two (or more) routers. Solution You can configure HSRP to use password authentication with the following commands:Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router1(config)#interface FastEthernet 0/1 ... [full story]

Showing HSRP State Information Problem You want to see current HSRP information, such as which router is primary. Solution To view the HSRP information, use the following EXEC command:Router2#show standby You can view the HSRP information for a specific interface with the following EXEC ... [full story]

Debugging HSRP Problem You want to debug an HSRP problem. Solution To debug all HSRP error events, use the following command:Router2#debug standby errors The events keyword will display information about HSRP events:Router2#debug standby events With the packets keyword, you can look at the contents ... [full story]

Routing Multicast Traffic with DVMRP Problem You want to route multicast traffic by using the DVMRP protocol. Solution Cisco routers support DVMRP only as a gateway to PIM. So the configuration is remarkably similar to the PIM configuration. The key difference is in the ... [full story]

DVMRP Tunnels Problem You want to create a DVMRP tunnel to bypass a section of network that doesn't support multicast. Solution You can create a DVMRP tunnel from a Cisco router to a nonCisco DVMRP device by using the special DVMRP tunnel mode. This ... [full story]

Configuring Bidirectional PIM Problem You want to use Bidirectional PIM to improve efficiency of your sparse-mode multicast network. Solution To use Bidirectional PIM, you must configure all of the routers in your network to support this method of building multicast forwarding trees. The RP ... [full story]

Controlling Multicast Scope with TTL Problem You want to ensure that your multicast traffic remains confined to a small part of the network. Solution You can define a TTL threshold value for each interface on a router. The ttl-threshold command instructs the router to ... [full story]

Controlling Multicast Scope with Administratively Scoped Addressing Problem You want to use RFC 2365 administratively scoped multicast addressing to control how multicast traffic is distributed through your network. Solution To configure regions of multicast scope using addressing rather than TTL, using the ip multicast ... [full story]

Exchanging Multicast Routing Information with MBGP Problem You want to exchange multicast routing information between two networks using MBGP. Solution Before setting up MBGP, you should set up multicast-routing on the Autonomous System Boundary Router (ASBR) and configure it to block multicast traffic that you ... [full story]

Using MSDP to Discover External Sources Problem You want to use MSDP to discover information about multicast sources in other Autonomous Systems. Solution The typical way to configure Multicast Source Discovery Protocol (MSDP) involves first selecting one of your MBGP routers as the RP ... [full story]

Configuring Anycast RP Problem You want to configure two or more RPs and have your routers simply use whichever one is closest. Solution One of the most significant shortcomings of PIM-SM is that within any given multicast network boundaries, there can be only one ... [full story]

Converting Broadcasts to Multicasts Problem You have a broadcast-based application that you want to treat as multicast so that it can cross the network. Solution Cisco has a special feature called an IP Multicast Helper, which you can use to convert broadcast packets to ... [full story]