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Pradeep H A
Beginner

Router interface bandwidth

Hi,

The physical Gigabit interface in this router has bandwidth command set & the show interface command output reflects the same

But how does the Subinterface get its bandwidth set to 100 Mbps? I always thought subinterfaces inherit the physical interface bandwidth. isnt it?

Router#sh int GigabitEthernet0/0

GigabitEthernet0/0 is up, line protocol is up

  Hardware is BCM1125 Internal MAC, address is 64ae.0c98.ba10 (bia 64ae.0c98.ba10)

  Description: link to PE

  MTU 1500 bytes, BW 10000 Kbit/sec, DLY 100 usec,

     reliability 255/255, txload 4/255, rxload 33/255

  Encapsulation 802.1Q Virtual LAN, Vlan ID  1., loopback not set

  Keepalive set (10 sec)

  Full-duplex, 100Mb/s, media type is RJ45

  output flow-control is XON, input flow-control is XON

  ARP type: ARPA, ARP Timeout 04:00:00

  Last input 00:00:00, output 00:00:00, output hang never

  Last clearing of "show interface" counters never

  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 111823

  Queueing strategy: fifo

  Output queue: 0/40 (size/max)

  5 minute input rate 1323000 bits/sec, 142 packets/sec

  5 minute output rate 177000 bits/sec, 96 packets/sec

     3331038420 packets input, 405011219 bytes, 0 no buffer

     Received 11024 broadcasts, 0 runts, 0 giants, 0 throttles

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

     0 watchdog, 0 multicast, 0 pause input

     0 input packets with dribble condition detected

     2480626113 packets output, 2746510267 bytes, 0 underruns

     1 output errors, 0 collisions, 3 interface resets

     0 unknown protocol drops

     0 babbles, 0 late collision, 0 deferred

     1 lost carrier, 0 no carrier, 0 pause output

     0 output buffer failures, 0 output buffers swapped out

Router#sh run int GigabitEthernet0/0

Building configuration...

Current configuration : 186 bytes

!

interface GigabitEthernet0/0

description link to PE

bandwidth 10000

no ip address

ip flow ingress

ip route-cache flow

duplex full

speed 100

media-type rj45

no cdp enable

end

Router#sh int GigabitEthernet0/0.2015

GigabitEthernet0/0.2015 is up, line protocol is up

  Hardware is BCM1125 Internal MAC, address is 64ae.0c98.ba10 (bia 64ae.0c98.ba10)

  Internet address is x.x.x.x/30

  MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,

     reliability 255/255, txload 4/255, rxload 32/255

  Encapsulation 802.1Q Virtual LAN, Vlan ID  2015.

  ARP type: ARPA, ARP Timeout 04:00:00

  Last clearing of "show interface" counters never

Router#sh run int GigabitEthernet0/0.2015

Building configuration...

Current configuration : 174 bytes

!

interface GigabitEthernet0/0.2015

encapsulation dot1Q 2015

ip address x.x.x.x 255.255.255.252

no cdp enable

service-policy output SE_SNAP_Q9000K_1M-0-7M-0_25

end

1 ACCEPTED SOLUTION

Accepted Solutions

Pradeep H A

Please see this link

http://www.cisco.com/en/US/docs/ios/12_3/interface/command/reference/int_a1g.html#wp1184839

This explains what happens with bandwidth on interfaces and sub interfaces

Regards,
Alex.
Please rate useful posts.

Regards, Alex. Please rate useful posts.

View solution in original post

4 REPLIES 4
Abzal
Rising star

Hi,

Bandwidth command under interface configuration is used by dynamic routing protocol such as EIGRP to calculate metric.
It does not affect to real bandwidth of interface.

Regards Abzal

Please rate helpful posts.

Sent from Cisco Technical Support iPhone App

Best regards,
Abzal

Pradeep H A

Please see this link

http://www.cisco.com/en/US/docs/ios/12_3/interface/command/reference/int_a1g.html#wp1184839

This explains what happens with bandwidth on interfaces and sub interfaces

Regards,
Alex.
Please rate useful posts.

Regards, Alex. Please rate useful posts.

View solution in original post

It is very important to define the Bandwidth statement if the access speed is different to the interface speed.

Capacity planning with gather uilisation against the bandwidth, so if it is wrong, you could get false positives, or worse, false negatives for utilisation.

Always good practice to code Bandwidth in any case (except where variable, e.g. DSL).


@STEVE CLARK wrote:

It is very important to define the Bandwidth statement if the access speed is different to the interface speed.

Capacity planning with gather uilisation against the bandwidth, so if it is wrong, you could get false positives, or worse, false negatives for utilisation.

Always good practice to code Bandwidth in any case (except where variable, e.g. DSL).


So are you saying if you interface speed is 1 Gig to use bandwidth to set it to 1 00mg?