Smurf Attacks, Directed Broadcasts, and RPF Checks
A smurf attack occurs when a host sends a large number of ICMP Echo Requests with some atypical IP addresses in the packet. The destination address is a subnet broadcast address, also known as a directed broadcast address. Routers forward these packets based on normal matching of the IP routing table, until the packet reaches a router connected to the destination subnet. This final router then forwards the packet onto the LAN as a LAN broadcast, sending a copy to every device..
The Level 2 capable routers in Figure 7-13 contain all the specific routes in their IP routing tables. For example, Router E has 18 specific routes in Example 7-18. Example 7-18. IS-IS Routes in the IP Routing Table of Router E E#show ip route | include L2 i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area i L2 156.26.2.0 [115/31] via 172.16.15.161, Serial0/0 i L2 156.26.3.0 [11..
Before moving into the configuration example, this section gives a brief overview of the operation of MIB and how it can be applicable to ELMI Address Registration. In Example 13-7, the snmp-server community command is configured on router R1 to allow SNMP Read Only access to the router using the "public" community string. The complete syntax for the snmp-server community command is as follows: Router(config)#snmp-server community string [view view-name] [ro | rw] [number] ..
Logging EIGRP Neighbor State Changes
When a neighbor relationship is lost, you also lose all of the routing entries for that neighbor. And the effects of this lost routing information are often felt throughout the network. Therefore, it can be extremely useful to have a good log of neighbor change events for troubleshooting strange intermittent network problems. However, this feature also gives you a good way of looking for faults on links that don't have a way of telling you about loss of connectivity. Two impo..
The timers basic command controls all of the adjustable timers for RIP: Router2(config-router)#timers basic 20 80 80 120 The four arguments are, in order, the update period, the invalid route timer, the holddown timer, and the flush timer. All of these times are in seconds. The update period controls how often the router sends updates to its neighbors. The default update period is 30 seconds. Reducing this period can help improve convergence times. However, you have to..
