Cisco ccie exam Analysis of Cisco CEF

Cisco ccie exam Analysis of Cisco CEF

Distributed exchange

With the introduction of the VIP (Versatile Interface Processor) card, the switching system of the router has gradually evolved to a peer-to-peer multiprocessor architecture.Cisco ccie exam. Each VIP card contains a RISC processor, maintains the latest copy of the fast switching cache generated by the routing switch processor, and can independently implement the function of routing and switching, and complete two types of switching at high speed---local VIP exchange and VIP exchange.

express exchange

As mentioned above, the fast-switching caching mechanism does not scale well in high-speed dynamic routing environments such as the Internet (often with network topology changes, routing changes, route flapping, etc.), and the routing changes cause the cache to be invalid. Rebuilding the cache (that is, the process of performing a "process exchange") is computationally expensive;At the same time, with the rapid development of the Internet and its services, various applications and interactive services based on WEB have increased the number of real-time data streams with a large number of communication times and short communication times, and the contents of fast-switched cache contents are constantly changing. The burden on the cache is increased, resulting in reduced router performance. The CEF Express Exchange Technology is designed to address these shortcomings.Cisco ccie exam

CEF is an advanced Layer 3 switching technology designed primarily for high performance, highly scalable Layer 3 IP backbone switching. To optimize the route lookup mechanism for packet forwarding, CEF defines two main components: the Forwarding Information Base and the Adjacency Table.Cisco ccie exam

The forwarding information base (FIB) is a lookup table in which the router determines the target exchange. There is a one-to-one correspondence between the FIB entry and the IP routing table entry, that is, the FIB is a mirror image of the routing information contained in the IP routing table. Since the FIB contains all the necessary routing information, there is no need to maintain the routing cache. When the network topology or route changes, the IP routing table is updated and the contents of the FIB change.Cisco ccie exam

The CEF uses the adjacency list to provide the information needed for the MAC layer rewriting of the packet. Each item in the FIB points to a next hop hop in the adjacency list. If neighboring nodes can forward each other through the data link layer, these nodes are listed in the adjacency list.

Once the adjacency is found, the system writes it to the adjacency list. The adjacency sequence is generated at any time. Each time a neighbor entry is generated, a link layer header information is pre-computed for that neighbor node, and the link is taken. The layer header information is stored in the adjacency list. When the route is decided, it points to the next network segment and the corresponding adjacency entry. It is then used for encapsulation when the packet is CEF exchanged.

To view information about the adjacency table, you can use the Cisco IOS command: show adjacency/show adjacency detail. When we look at the adjacency table information, we find the following two main types of adjacency: Host adjacency and Point to Point.Cisco ccie exam The usual display of the Host adjacency type is an IP address, which indicates the adjacent next hop IP address; the Point to Point type display is "point 2point", indicating that this is a point-to-point circuit. There are also other special types, such as Null adjacency, Glean adjacency, etc.

CEF is a high-speed switching method designed for high-performance, highly scalable IP backbone networks. From the above introduction, it is not difficult to see that in large-scale dynamic IP networks, CEF can provide unprecedented consistency and stability of exchange.It can effectively compensate for the frequent failure of fast-switching cache entries. The dCEF distributed exchange enables each line card to be completely exchanged, providing superior performance.CEF has less memory than fast-switched routing caches and provides load balancing, network accounting, and more. With the help of CEF Express switching technology and other revolutionary innovations, Cisco's GSR routers have achieved great success worldwide.

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Cisco ccie exam Analysis of Cisco CEF

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