Since stub areas cannot carry external routes, type 5 advertisements are not allowed in stub areas. Since type 5 LSAs are not allowed in stub areas, ASBRs cannot be located in stub areas. The problem is that sometimes the best solution to a design problem is to allow external routes. This problem is solved with not-so-stubby areas (NSSA). An NSSA can be not-so-stubby or not-so-(totally)-stubby; either way an NSSA is a stub area that allows an ASBR. The ASBR understands..
Subnetting a Classful Network Number
With classful addressing, and no subnetting, an entire class A, B, or C network is needed on each individual instance of a data link. For example, Figure 4-1 shows a sample internetwork, with dashed-line circles representing the set of hosts that must be in the same IP network—in this case requiring three networks. Figure 4-1 shows two options for how IP addresses may be assigned and grouped together for this internetwork topology. Option 1 uses three classful networks; ..
Logging Unauthorized SNMP Attempts
Use the following commands to configure your router to log unauthorized SNMP requests: Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#access-list 99 permit 172.25.1.0 0.0.0.255 Router(config)#access-list 99 permit host 10.1.1.1 Router(config)#access-list 99 deny any log Router(config)#snmp-server community ORARO ro 99 Router(config)#snmp-server community ORARW rw 99 Router(config)#end Router# If you are concerned ..
Using Better Password-Encryption Techniques
Cisco introduced the enable secret password to improve the security of the enable password command. This command uses the cryptographically strong MD5 algorithm to encrypt passwords. It it extremely difficult to crack this algorithm. In fact, there are no known ways to uniquely reverse MD5 encryptions, which is why it is called a nonreversible algorithm. When you configure the router with an enable secret password, it will encrypt your enable password whether you have the se..
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 configure load-balancing for equal cost paths: Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router1(config)#router bgp 65500 Router1(config-router)#maximum-paths 4 Router1(config-router)#exit Router1(config)#end Router1# This option is useful when there are multiple paths to a particular adjacen..
