MultiLayerSwitch often used instead of router to route inter-valn for purely economic issues. Swicth a multi layer has a higher density of ethernet ports of a router, may even have cost a third less and is only concerned with routing / switching inter-VLAN.
L3 switches are equipped with a specialized hardware chips called ASICs (Application-Specific Integrated Circuits) whose job it is to perform routing between the Ethernet ports, at high speed.
difference between L3 and Routing swiching
The process of routing IP packet can eseere divided into two processes:
-> Control Plane
in charge of creating the routing tables, ARP table 
-> Data Plane
-> Data Plane in charge instead of simply making the routing of packets
The difference Switch between Router and L3 data plane is implemented as is. Inside the Control Plane, there is a general purpose CPU, programmed by different vendors, with the routing algorithms. E 'waving bright then the control plane is responsible for creating the routing tables and update them as soon as there is a change of topology. The Control Plane indicates where then rotate the packages. So Control Plane working in the "software". Conversely
the Data Plane indicates
rotate as the packages, then a far more 'simple, practically consists in making the rewrite of the MAC to be forward. Swicthes The difference between Router and L3 is right in the data plane:
-routers implement the data plane within the CPU dedicated to the Control Plane, and then works in a software- the switches implement the data plane hardware through mode the ASIC. The routing is increasingly veòloce hardware than the software. In general, when a router receives a package and must forword performs the following operations: 1) To determine if the destination is reached 2) Determine the next-hop and output interface of the package
3) Make the rewrite of the MAC, or replace the source address and destination of the packet at Level 2 received, with its own MAC and the MAC of the next hop (for this purpose using an ARP request)
packages using a router forwarding to:
-Fast-Switching Process switchng (Interrupt Context Switching) -CEF (Interrupt Context Switching)
Process switching
E 'the traditional method used in the past, supported by all devices and all of the IOS, now used only for throubleshooting.
The router receives the packet, performs the analysis of the destination IP address, figure out where to send the packet, performs the MAC rewrite, recalculates the CRC and sends the package, all of this software.
It 's a method that consumes so much CPU is used only for this reason being throubleshooting.
Now, if you have Process Switching: The decision to
-forwarding and info used to make the rewrite of the MAC are taken and read or RIB table (Route Information Table) or ARP cache
-package and switch to sull'IOS a process running on the router and that does not stop when involved in another process running on the router then itself.
Interrupt Context Switching
is another switching methods used by Cisco routers. In this case, the MAC rewrite info is read from a cache and also the task of packet forwarding stops processes running at that time sull'ios.
cache is built according to the following methods:
-CEF-switching Fast
Fast switching (based on route caching)
the MLS that have aspects of both L2 L3, in principle used the philosophy "route one, swicth many. The fast
swicthing uses the concept of flow, which is a set of packages that belong to the same Protocol and that have the same source and same destination. The route processor receives the first packet, makes a routing decision and forwards. The switch engine look at the package forward and if he can "see" the packet that arrives or is sent from router to router, then intervenes and is used as a shortcut path for forward future packets in this stream. This is an example of route caching
.
Then the first packet and forward in the next software in hardware.
When the route processor receives a packet and decides to forward, a cache write this info table (hardware forwarding table, contained in 'ASIC) and all future packets on this flow are switch via hardaware.
The important concept is that until you get the package to the router, the router is unable to populate the cache hardware.
Topology-based switching
This method is based on CEF
route caching differs from the fact that in this case, the cache table (FIB and Adiajency Table) created in hardware are populated based on route table and arp table, without the need to populate them after forwarding the first received packet. Thus, unlike the route caching, all packages are Forward in hardware. To understand the advantage over the route caching is enough to think that in the latter If, for any stream created (VoIP phone, connection FTP, HTTP request etc,) is always the first packet forwarding to a software! And 'this can create slow compared to hardware forwarding.
The key concept is that the Control Plane and Data Plane are perfectly separated by ASIC, and then both are implemented in hardware.
FIB Table
TABLES USED IN SWITCHING
0 comments:
Post a Comment