WAN performance configuration Directory

Realized information

Task list of Fast switch configuration

Configure global fast switch enable

Configure fast switch enable on the interface

link layer protocol of fast switch supported by link layer

link layer protocol of fast switch not supported by link layer

L2TP function’s influence on fast switch  

Influences to other module after enabling fast switch

 

Realized information

Fast switch realization will elevate packet forward speed. Fast switch adopts information flow technology and uses cache memory to process received packets. When the first data flow packet is forwarded by search route table, if it is configured fast switch, it is going to exchange router information in cache memory. When forwarding the succeeding packets, the packets will pass through cache memory exchange information and forward the packet directly. This simplifies the process for supporting some special functions under ordinary forward method. It also improve link layer buffer mechanism and enhance packet forward efficiency.
After enabling global fast switch and both forwarding and receiving ports are configured, fast switch works.

Task list of Fast switch configuration

To configure  fast switch requires the implementation of the following tasks:

Configure global fast switch enable

Configure fast switch enable on the interface

 

Configure global fast switch enable

First you should configure global fast switch enable under global configuration mode, then you are able to cinfigure fast switch on the interface.

command

function

Ip fast-switch enable

 Open the Global fast switch enable

 

Configure fast switch enable on the interface

Then configure the fast switch function on the interface needs to perform fast switch under interface configuration mode.

command

function

Ip fast-switch enable

Open  the fast switch enable on the interface

 

 

link layer protocol of fast switch supported by link layer

    Ethernet

    PPP

    HDLC

link layer protocol of fast switch not supported by link layer

    SLIP

    X25

    FR

    SDLC

  Protocols like x25,SLIP are applied in low speed DDN line. The limit of forwarding packets are not the efficiency of router forwarding but the line bandwidth.

Because X25 does not support fast switch, XOT and X25-TCP related functions closely connected to X25 are not affected by fast switch.

   

L2TP function’s influence on fast switch

         When an interface configuration is packed with PPP, and the PPP is configured with L2TP related command during negotiation, the port fast swich function fails. The reason for failure is that the port does not process IP packets anymore but forward them to remote LNS after receiving Client PPP packets.

 

Influences to other module after enabling fast switch

    IP Acces List

    IPSec(tunnel mode)

    NAT

    RSVP

   Because fast switch realization disable some special function on IP layer to enhance forward speed, some special functions that deals with IP pakets will be influenced.

Influenced functions including the following. If the port is configured with fast switch, the port corresponding function as follow will be invalid.

 

 IP Acces List   IP access list related functions

   Because fast switch enhance forward efficiency, the function’s determination function is masked and it is invalid.

Note: notice that access list invalid means when a port is configured with fast switch, the port IP packet access list function fails. Other ports that are not configured with fast switch functions still works.

    IPSec(tunnel mode)

    When realizing IPSec function, the IP packets need to be encrypted/decrypted. When processing IPSec packet head, outer IP packet head are also added/deleted. Because the function occupies much CPU resource, fast switch will mask this function and makes it invalid.

NAT

While realizing NAT functions, it requests analysis for IP packet TCP or UDP types, and port number analysis. The function is maily applied to stub network router. After configuring fast switch, it is believed that the router is mainly functioned for forwarding packets instead of the access function in the user side, so the forward functions which affect the efficiency so much will be masked.

Similar to access list, NAT outside address transformation and inside address transformation are invalid after configured fast switch. The NAT related functions are still working.

RSVP

After configured fast switch, it will try its best to forward the packets  without considering saving the resource.