Router: Interface has more bandwidth then the configured

Unanswered Question
Nov 20th, 2009

Hi,

I have two routers connected each other using lease line. The bandwidth between them is 1 Mbps. but i am seeing nearly 2 mbps leaving from Router-1 to Rouer-2. how it is possible? is i am looking in the wrong way? the output is from the serial interface on both routers.

Router-1

interface Serial0
bandwidth 1024
ip address 10.10.10.1 255.255.255.252
end


Serial0 is up, line protocol is up
  Hardware is QUICC Serial
  Description: * South-Router *
  Internet address is 10.10.10.1/30
  MTU 1500 bytes, BW 1024 Kbit, DLY 20000 usec,
     reliability 255/255, txload 253/255, rxload 31/255
  Encapsulation HDLC, loopback not set
  Keepalive set (10 sec)
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters 41w1d
  Input queue: 23/75/0/0 (size/max/drops/flushes); Total output drops: 193755
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/193755 (size/max total/threshold/drops)
     Conversations  0/31/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 768 kilobits/sec
  5 minute input rate 126000 bits/sec, 134 packets/sec
  5 minute output rate 1986000 bits/sec, 210 packets/sec
     790114604 packets input, 3258179720 bytes, 2474 no buffer
     Received 2905199 broadcasts, 0 runts, 30 giants, 3159 throttles
     33171 input errors, 23120 CRC, 7997 frame, 0 overrun, 0 ignored, 2054 abort
     1009731639 packets output, 491591296 bytes, 0 underruns
     0 output errors, 0 collisions, 240 interface resets
     0 output buffer failures, 0 output buffers swapped out
     4 carrier transitions
     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up


***************************************************************************************************************************

Router-2

interface Serial0
bandwidth 1024
ip address 10.10.10.2 255.255.255.252
end

sh int serial 0
Serial0 is up, line protocol is up
  Hardware is QUICC Serial
  Description: * North-Router*
  Internet address is 10.10.10.2/30
  MTU 1500 bytes, BW 1024 Kbit, DLY 20000 usec,
     reliability 255/255, txload 30/255, rxload 252/255
  Encapsulation HDLC, loopback not set
  Keepalive set (10 sec)
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters 41w1d
  Input queue: 1/75/0/0 (size/max/drops/flushes); Total output drops: 22670
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/22405 (size/max total/threshold/drops)
     Conversations  0/18/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 768 kilobits/sec
  5 minute input rate 1990000 bits/sec, 210 packets/sec
  5 minute output rate 121000 bits/sec, 129 packets/sec
     1009750041 packets input, 518574419 bytes, 1 no buffer
     Received 2906175 broadcasts, 0 runts, 185 giants, 1 throttles
     9306 input errors, 4205 CRC, 3988 frame, 0 overrun, 0 ignored, 1103 abort
     790300876 packets output, 3277362537 bytes, 0 underruns
     0 output errors, 0 collisions, 260 interface resets
     0 output buffer failures, 0 output buffers swapped out
     1672 carrier transitions
     DCD=up  DSR=up  DTR=up  RTS=up  CTS=up


**************************************************************

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Jon Marshall Fri, 11/20/2009 - 07:45

The bandwidth statement does not reflect the actual bandwidth of the link ie. if the bandwidth is more adding a bandwidth statement would not limit it to that.

The bandwidth statement is actually used for QOS and by certain routing protocols such as EIGRP. That is why you should actually make the bandwidth statement reflect the actual "true" bandwidth of the line.

Jon

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