Hell Really Exists
Because of this increased focus on network security, network administrators often spend more effort protecting their networks than on actual network setup and administration. New tools that probe for system vulnerabilities, such as the Security Administrator Tool for Analyzing Networks (SATAN), assist in these efforts, but these tools only point out areas of weakness instead of providing a means to protect networks. Thus, as a network administrator, you must constantly try to keep abreast of the large number of security issues confronting you in today's world. This chapter describes many of the security issues that arise when connecting a private network to the Internet.
The NetRanger Sensor is now ready to initiate shunning by writing a dynamic ACL to the router's Serial0 interface. The next major step is to decide which signatures trigger a shun response. This type of automated response by the Sensor should only be configured for attack signatures with a low probability of false positive detection, such as an unambiguous SATAN attack. In case of any suspicious activity that does not trigger automatic shunning, you can use a Director menu function to shun manually.
The first problem that occurs when engineers are asked to work on new projects is that they are often given rather sloppy guidelines, such as it must be secure, without any further explanation. One of the issues here is, as explained previously, that the term secure needs to be defined in painfully precise terms before it can be implemented. As with many things, the devil is in the details Furthermore, security requirements can be a moving target as organizations evolve.
Because you captured CDP packets, take time to analyze them in the protocol analyzer trace in Figure 5-20. If you are curious about the 804 router in my display, it is just being used as hub to connect some devices together. Confirm that CDP messages occur every 60 seconds and that they use the destination multicast address of 01000ccccccc as in line 7 of Figure 5-20. Also notr the EIGRP AO 500 mu ltica st hell os over 22.214.171.124.
By exchanging hello packets, a router determines the reachability of its neighbors and uses this information to establish adjacency. Adjacency is a record that a router keeps about the state of its connectivity with a neighbor and the attributes of the neighboring router. The router stores Establishing router adjacency over a WAN involves first establishing the underlying data-link connection (details depend upon the medium). The routers then exchange identities by using the IPX WAN Version 2 protocol and determine certain operational characteristics of the link. Hello packets are exchangedt and the routers update their adjacency databases. The routers then exchange both link-state packets (LSPs) describing the state of their links and IPX data packets over the link. To maingain a WAN link, the router maintains a state variable indicating whether the link is up, down, or initializing for each adjacency. If the router does not hear from a neighbor within the time specified in a holding...
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