How to limit network bandwidth

Managing network bandwidth is becoming more and more important. On a network with no other routers, it makes no sense to route the broadcast traffic that flows out of the network interface. This is very inefficient for your network bandwidth and router resource usage. Let's take a look at how to better bandwidth control by using the Passive-interface command.

To properly configure the routing protocol, the Passive-interface command must not be unknown. However, if you are not using a dynamic routing protocol (such as OSPF,EIGRP, or RIP), you will not be using this command.

The Passive-interface command works only in router configuration mode (Router Configuration mode). When you see a command prompt like the one below, you know you're in the mode: Router (Config-router)

You can use the Passive-interface command to tell the dynamic routing protocol not to send webcasts over this interface. This command can take effect on all IP routing protocols except BGP.

However, the command works on OSPF and is somewhat different from the Is-is. With OSPF, the passively specified network interface appears as a stub (the distal region) and does not send and receive any route updates. When using RIP,IGRP, and EIGRP, it does not send any routes, but it can receive them. Similarly, it will send broadcasts to all the passive interfaces on the network.

There are two ways to use the Passive-interface command.

Specifies that an interface becomes passive mode, which means that it will not emit a route update.

First, all interfaces are set to passive mode. Then, on the interface where you intend to send routing updates, use the No Passive-interface command.

Let's look at one example for each of two ways. Note: Two cases assume that you have previously added a network with a passive interface to the routing protocol (using network commands).

Let an interface become passive mode, only the interface must be specified. Here is an example:

Router (config) # Router rip Router (config-router) # Passive-interface Ethernet 0/0
To set all interfaces passive, and then open an interface individually, use the passive-interface default and no Passive-interface commands (described in iOS 12.0). Here's an example:

Router (config) # Router rip Router (config-router) # passive-interface default Router (config-router) # No Passive-interface Serial 0/0

Let's look at a simple network dedicated to demonstrating the deep application of the command. Suppose you have 2 routers connected through a T1 loop, and the router runs RIP. Each router is connected to a local area network, and the computer is connected to the LAN via an Ethernet card.

You need each router to know the other router's network, right? This is why the use of dynamic routing protocols is the purpose. However, on the local area network, there is no other router to allow the two routers to exchange routing updates.

In this case, why do you want to broadcast a routing update every 30 seconds on the LAN interface, continuing? The answer is you don't want to. This is a waste of LAN bandwidth and computer CPU time. If it's just a minor update, it does not cause any problems, but if you can avoid it, why send this unnecessary communication?

How can we eliminate this needless communication? On each router, into RIP configuration mode (RIP Configuration mode) and use the Passive-interface command to stop sending routing updates on the LAN port. Here is an example:

Router (config) # Router RIP Router (config-router) # Passive-interface Ethernet 0/0

This, of course, assumes that you have already used the Internet command to configure the network you intend to broadcast. Here is an example:

Router (config-router) # network 1.0.0 ... 0 (the serial network)

Router (config-router) # network 2.0.0.0 (The Ethernet Network)

Remember, this means that the system will broadcast the two networks you set up by connecting to another router's serial interface. Also, this does not prevent your router from receiving routing updates from the local Area network interface (using RIP). If another router happens to be on the local area network and sends an update to your router, it can still receive these updates.