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..
Purposefully Resetting BGP Peer Connections
Example 12-3 shows how to reset neighbor connections by using the neighbor shutdown command and, along the way, shows the various BGP neighbor states. The example uses routers R1 and R6 from Figure 12-2, as configured in Example 12-2. Example 12-3 Examples of Neighbor States All BGP neighbors can be reset with the clear ip bgp * exec command, which, like the neighbor shutdown command, resets the neighbor connection, closes the TCP connection to that neighbor, ..
Contents of the Neighbor Table
The neighbor table includes the following information: • The Layer 3 address of the neighbor. • The interface through which the neighbor's Hello was heard. The holdtime, or how long the neighbor table waits without hearing a Hello from a neighbor, before declaring the neighbor unavailable and purging the database. Holdtime is three times the value of the Hello timer by default. • The uptime, or period since the router first heard from the ne..
Multiplexing is a fundamental element of network design. Indeed, you could argue that a network is typically one huge multiplexing system. More specifically, however, multiplexing is a tool that provides economies of scale—multiple users share one large resource rather than a number of individual resources. NOTE Multiplexing is the aggregation of multiple independent traffic flows into one large traffic flow. A useful analogy is the freeway system, which mul..
The first version sends all packets destined to the single host 10.35.15.5 out through the Ethernet0 interface. In this case, the router will need to figure out which device on this segment to forward the packet to, because it must put the MAC address of the next hop router in the Layer 2 frame header. The standard mechanism for associating IP addresses with MAC addresses is the Address Resolution Protocol (ARP). The router will send out an ARP request onto the Ethernet segme..
