ACLs can degrade a router's performance. The effect of processing ACLs on a busy router can be significant. Here are some of the rules you should keep in mind while implementing ACLs on a router so as to minimize their impact on performance: ACLs are processed in a top-down manner. The packets are inspected first against the topmost entry in the access list, and then the access list is worked downward until a hit is made. (If no hit is made on an ACE in the access list, the..
Determining Whether the LSP in the Database Is Valid
The LSP contains three fields that help determine whether the LSP that has been received is more recent than that held in the database, and whether it is intact or has been corrupted. These three fields are as follows: • Remaining Lifetime— This is used to age-out old LSPs. If an LSP has been in the database for 20 minutes, it is assumed that the originating router has died. The refresh timer is set to 15 minutes. If the lifetime expires, the LSP has the con..
The log-adjacency-changes Command
The log-adjacency-changes command is very useful because it tracks changes. In link-state protocols, it is very important to keep track of the neighbors. This command identifies any changes to the adjacencies and link flaps. The configuration for router B here is as follows: hostname router B router IS-IS MKS net 39.0001.0000.0000.0001.00 log-adjacency-changesThe output of this command is: routerB # sh log %CLNS-5-ADJACEN..
802.1Q: VLANs and Vendor Interoperability
Because vendors took individual approaches to create VLANs, network administrators were impaired whenever multiple vendor solutions were introduced into their system. A multi-vendor VLAN must be carefully handled to deal with interoperability shortcomings. Recognizing this deficiency in the industry, IEEE commissioned the 802.1Q committee to develop a vendor-independent method to create interoperable virtual bridged local area networks. IEEE 802.1Q describes concepts called ..
Use the NTP and clock show commands to verify the status of NTP on your router. The best place to start is the show clock detail command, which provides information on the current time, time source, and time zone configuration: Router>show clock detail 15:54:33.079 EST Sun Jan 29 2006 Time source is NTP Summer time starts 02:00:00 EST Sun Apr 2 2006 Summer time ends 02:00:00 EDT Sun Oct 29 2006 Router> To display the current NTP status of the local router, the comman..
