Chapter 31. The Congested Network

A congested network is one where there’s too much data, and not enough bandwidth to support it. QoS can help with a congested network, but it cannot cure the root problem. The only ways to cure congestion on a network are to add more bandwidth, or reduce the amount of data trying to flow over it. That being said, let’s look at a congested network, and see how we might fix it.

Determining Whether the Network Is Congested

How do you know if your network is congested? Let’s look at our favorite two-building company again (Figure 31-1).

Typical two-building network

Figure 31-1. Typical two-building network

Users have been complaining that access to the other building is slow. So, let’s take a look at the interfaces on one of the routers that connects the T1 between buildings. Here’s the output from the show interface command for the serial interface on Building B’s router:

Bldg-B-Rtr#sho int s0/0
Serial0/0 is up, line protocol is up
  Hardware is PowerQUICC Serial
  Description: <[ T1 WAN Link ]>
  Internet address is
  MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
     reliability 255/255, txload 42/255, rxload 249/255
  Encapsulation PPP, loopback not set
  Keepalive set (10 sec)
  LCP Open
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters 3w4d
  Queueing strategy: fifo
  Output queue 0/40, 548941 drops; input queue 0/75, 3717 ...

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