Go Premium for a chance to win a PS4. Enter to Win

x
  • Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 86
  • Last Modified:

What is relation between speed and bandwidth when it is under interface mode?

Hi In the interface mode, we have two choices to configure, speed and bandwidth. What is relation between the speed and bandwidth? Thank you
0
eemoon
Asked:
eemoon
  • 7
  • 4
  • 3
  • +1
1 Solution
 
John HurstBusiness Consultant (Owner)Commented:
They are sometimes used interchangeably.

Speed is normally the native speed of the device or circuit. E.g. a 1 Gbit/second network card.

Bandwidth is normally the speed of supply. Your internet may be supplying 20 Bits/second even though your router is capable of more.

Configure bandwidth in your example above for the highest available unless you are trying to constrain it in some way.
0
 
Jan SpringerCommented:
In Cisco kit, "bandwidth" is an identifier to higher level protocols.  It can be used to de-prefer or prefer one interface over another.  It has no real impact on throughput.

Speed identifies the negotiation of the ethernet interface.

If you ever desire to restrict bandwidth on an interface, you want to use QoS: class-maps, policy-maps, access-lists, etc and apply the policy to the interface.
0
 
eemoonAuthor Commented:
Thank you so much for your reply.

Speed identifies the negotiation of the ethernet interface

Can you explain it?

If we use "speed 100" under interface, or "speed 1000", what is difference between the two?
0
Concerto's Cloud Advisory Services

Want to avoid the missteps to gaining all the benefits of the cloud? Learn more about the different assessment options from our Cloud Advisory team.

 
Jan SpringerCommented:
100M vs 1000M (or 100M and 1G).

If you use "speed 100" on a gigabit interface and both end negotiate properly, you have throttled the max throughput to 100M.
0
 
John HurstBusiness Consultant (Owner)Commented:
That is what I was suggesting when I said you could set speed/bandwidth to constrain overall bandwidth used.
0
 
Jan SpringerCommented:
Not with the "bandwidth" command.  It's used for route preference.  

Only "speed" (which is limited) or QoS can change input and output throughput.
0
 
John HurstBusiness Consultant (Owner)Commented:
That is for Cisco I assume
0
 
Jan SpringerCommented:
Yes.  That's why I mentioned it "with Cisco kit ... ".

But, Brocade doesn't have the "bandwidth" command and I believe Juniper does not either.  

I can't recall Adtran.
0
 
Craig BeckCommented:
Bandwidth is better considered as capacity instead of speed.

Imagine a road.  With 1 lane your car can travel at a maximum speed of 100Mph.  If you add another lane you don't make the car go faster, but instead you add capacity.

In a circuit, if you have a 200Mbps connection you'd usually have a 1Gbps bearer, so the speed is 1Gbps but the bandwidth is 200Mbps.
0
 
Jan SpringerCommented:
No, Craig.

The author didn't ask for a definition of "bandwidth".  He asked how the "bandwidth" command is used within an interface configuration.
0
 
eemoonAuthor Commented:
"bandwidth" is capacity concept, while "speed" is close to real traffic concept, but we can setup the "speed" to limit the traffic flow. and in the same physical interface, "bandwidth" is greater than "speed" am i right?
0
 
Jan SpringerCommented:
There is no relationship.  You cannot compare the two commands.

"bandwidth" is not relative to speed or capacity but is used to influence your interior routing.  

It has no impact on the throughput of the interface.
0
 
eemoonAuthor Commented:
"bandwidth" is not relative to speed or capacity but is used to influence your interior routing.  

What does "bandwidth" impact on? Thank you
0
 
Jan SpringerCommented:
Interior routing protocols -- such as OSPF -- will use the bandwidth configured on an interface to determine cost.  

Cost is a routing metric that determines which path is more preferred over another.

When you configure it, you *do not change the maximum throughput based upon the negotiated speed/duplex on the interface*

So:

interface Gi1/0/1
  bandwidth 100
  speed 1000
  duplex full

You are telling OSPF to not prefer this interface where another interface has "bandwidth 1000" (or whatever the actual syntax is).  This does not prevent the downstream device from consuming 1G.  It can.

If your other interface is 100M, then, everything else being equal, both paths will be equally preferred.

Some tools will also use that in configuring thresholds (i.e., MRTG).
1
 
Craig BeckCommented:
Jan is spot on.  Just to add, the bandwidth command doesn't affect the interface at all; only protocols that use the interface.  The speed command directly affects the interface, not protocols that use the interface.
0
 
eemoonAuthor Commented:
Thank you Jan,  and Craig and john. Jan is right and gave very clear explanation.
0

Featured Post

New feature and membership benefit!

New feature! Upgrade and increase expert visibility of your issues with Priority Questions.

  • 7
  • 4
  • 3
  • +1
Tackle projects and never again get stuck behind a technical roadblock.
Join Now