Cisco IOS

Logging EIGRP Neighbor State Changes Problem You want to log EIGRP neighbor state changes. Solution To enable the logging of EIGRP neighbor state changes, use the eigrp log-neighbor-changes configuration command: Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router1(config)#router eigrp 55 Router1(config-router)#eigrp log-neighbor-changes Router1(config-router)#exit Router1(config)#end Router1# Another ... [full story]

Limiting EIGRP's Bandwidth Utilization Problem You want to limit the fraction of an interface's bandwidth available to EIGRP for routing updates. Solution To modify the amount of bandwidth percentage available to EIGRP, use the ip bandwidth-percent configuration command: Router1#configure terminal Enter configuration commands, one per ... [full story]

EIGRP Stub Routing Problem You want to stabilize your network by sending smaller routing tables out to stub branches and reducing the scope of EIGRP queries. Solution To enable stub routing, use the eigrp stub configuration command: Router1#configure terminal Enter configuration commands, one per line. ... [full story]

Route Tagging Problem You want to tag specific routes to prevent routing loops while mutually redistributing routes between two routing protocols. Solution This example shows how to tag external routes in EIGRP: Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router1(config)#ip ... [full story]

Changing the Network Type on an Interface Problem You want to change the default OSPF network type on an interface. Solution OSPF supports several different types of logical networks on interfaces. The default values are often exactly what you want, but it is sometimes ... [full story]

OSPF Route Tagging Problem You want to tag specific routes to prevent routing loops during mutual redistributing between routing protocols. Solution You can tag external routes in OSPF by using the redistribute command with the tag keyword: Router1#configure terminal Enter configuration commands, one per line. ... [full story]

Logging OSPF Adjacency Changes Problem You want to monitor OSPF adjacency state changes to ensure network stability. Solution The log-adjacency-changes configuration command instructs the router to create a log message whenever two OSPF routers establish or break their adjacency relationship: Router2#configure terminal Enter configuration commands, ... [full story]

Filtering BGP Routes Based on AS Paths Problem You want to filter the BGP routes that you either send or receive based on AS Path information. Solution You can use AS Path filters, either inbound or outbound, to filter either the routes you ... [full story]

Reducing the Size of the Received Routing Table Problem You want to summarize the incoming routing information to reduce the size of your routing table. Solution One of the easiest ways to reduce your routing table size is to filter out most of the ... [full story]

Summarizing Outbound Routing Information Problem You want to summarize your routing table before forwarding it to another router. Solution BGP includes an automatic summarization feature that is on by default: Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router1(config)#router bgp 65500 Router1(config-router)#neighbor 192.168.1.5 remote-as ... [full story]

Prepending ASNs to the AS Path Problem You want to increase the length of an AS Path so that one inbound path looks better than another. Solution In situations when you have multiple connections between ASs, you will often want to make remote networks ... [full story]

Redistributing Routes with BGP Problem You want to redistribute routes between an IGP and BGP. Solution When connecting two or more IGPs using BGP, you sometimes need to configure redistribution between the IGP and BGP on both routers. To make the example more interesting, ... [full story]

Using Peer Groups Problem You want to apply the same options to several peers. Solution Peer groups allow you to apply the same BGP configuration to a number of neighbors at the same time: Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router1(config)#router ... [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]

Using BGP Communities Problem You want to configure BGP Communities to control routing and route propagation. Solution Configuring Cisco routers to use BGP Communities is a two-step process. You must specify the desired Community values by using a route map associated with a neighbor ... [full story]

Using BGP Route Reflectors Problem You want to simplify your iBGP peer relationships by using route reflectors. Solution There are three types of configurations to consider when working with BGP Route Reflectors: the Route Reflector itself, the Client Peer, and the Nonclient Peer. In ... [full story]

Putting It All Together Problem You want to combine all of best the elements in this chapter to create a good redundant ISP connection. Solution For simplicity, we will extend the single router dual ISP configuration of Recipe 9.4 rather than the dual router ... [full story]

Removing Private ASNs from the AS Path Problem You want to prevent your internal private ASNs from reaching the public Internet. Solution You have to be extremely careful that any unregistered ASNs that you may be using don't propagate into the public Internet. In this ... [full story]

Load-Balancing Problem You want to load-balance traffic over two or more links, between two eBGP or iBGP neighbors. Solution Although BGP goes to great lengths to ensure that there is only one path for each route by default, Cisco routers also allow you to ... [full story]

Restricting Networks Advertised to a BGP Peer Problem You want to restrict which routes your router advertises to another AS. Solution There are three ways to filter routes in BGP. The first one uses extended access lists and route maps, as follows: Router1#configure terminal Enter ... [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]

Reducing OSPF Traffic in Stable Networks Problem You have a stable network that doesn't require all of the overhead of LSA flooding. Solution You can reduce the overhead due to OSPF LSA flooding by applying the interface-level command ip ospf flood-reduction: Router9#configure terminal Enter configuration commands, ... [full story]

OSPF Virtual Links Problem You want to configure a virtual link between two routers to link up a fragmented Area. Solution Use the area virtual-link command to configure an OSPF virtual link between two routers: Router9#configure terminal Enter configuration commands, one per line. End with ... [full story]

Viewing OSPF Status with Domain Names Problem You would prefer to view proper domain names rather than see the raw IP addresses in the output of your OSPF show commands. Solution You can configure OSPF to resolve IP addresses into router names with the ... [full story]

Debugging OSPF Problem OSPF is not behaving properly, and you want to debug it to isolate and solve the problem. Solution There are several OSPF debugging options. But usually, if there is an OSPF problem, you will see it as instabilities in the neighbor ... [full story]

Configuring BGP Problem You want to run BGP in a simple network. Solution In its simplest configuration, BGP exchanges routes between a router in one AS and another router in a different AS. The first router is in AS 65500: Router1#configure terminal Enter configuration commands, one ... [full story]

Using eBGP Multihop Problem You want to use BGP to exchange routes with an external peer router that is more than one hop away because the router at the edge of the network doesn't support BGP. Solution Cisco provides a useful option called eBGP ... [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]

Connecting to Two ISPs Problem You want to set up BGP to support two redundant Internet connections. Solution The following configuration shows how to make the basic BGP connections, but it has serious problems that we will show how to fix in other ... [full story]

Connecting to Two ISPs with Redundant Routers Problem You want to connect your network to two different ISPs using two routers to eliminate any single points of failure. Solution In this example, we have two routers in our AS, which has ASN 65500. The ... [full story]

Setting Up Frame Relay with Point-to-Point Subinterfaces Problem You want to configure Frame Relay services so that each PVC is assigned to a separate subinterface. Solution Probably the cleanest way to set up a Frame Relay network is to use point-to-point subinterfaces. If you ... [full story]