OSPF optimizes the LSA flooding process on multiaccess data links by using the concept of a designated router (DR). Without the concept of a DR, each pair of routers that share a data link would become fully adjacent neighbors. Each pair of routers would directly exchange their LSDBs with each other as shown in Figure 10-1. On a LAN with only six routers, without a DR, 15 different pairs of routers would exist, and 15 different instances of full database flooding would occur...
PIM sparse mode works the opposite way of dense mode. PIM dense mode assumes that all the multicast interfaces are interested in multicast packets, unless being told otherwise. In PIM sparse mode, the router assumes that none of the multicast inter-faces is interested in receiving multicast packets, unless a PIM join message is received on the interface. PIM sparse mode is more scalable than PIM dense mode, but the concept is more complex. PIM sparse mode uses the concept of ..
When new hosts join a group, routers may need to change the current SPT for a particular (S,G) entry. With PIM-DM, one option could be to wait on the pruned links to expire. For example, in Figure 20-9, R3 could simply quit sending State Refresh messages, and within 3 minutes at most, R3 would be receiving the multicast packets for some (S,G) SPT again. However, waiting on the (default) 3-minute Prune timer to expire is not very efficient. To allow routers to “unprune” a ..
LDP Control-Plane and Forwarding-Plane Components
The state of an LSP that is established through LDP can be divided into two components: the LDP state (which is maintained in the control plane), and the MPLS forwarding state (which is maintained in the forwarding plane). The exact format of the LDP state or the MPLS forwarding state of an LSP in an LSR depends on whether the LSR is ingress, egress, or transit for that LSP. For example, LSP ingress LSR uses a FEC-to-NHLFE (FTN) entry to map the associated FEC to one or more..
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..
