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New Member

Recommended maximum ethernet link utilization

Hi,

For WAN links the recommended maximum utilization should not exceed 70%, but what about ethernet links or etherchannels? what percent of an ethernet link bandwidth should I leave free of user data? Where can I find a Cisco document talking about that?

Thanks.

Agustin

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Bronze

Re: Recommended maximum ethernet link utilization

For situation 1, the 2960 can handle the 100/1000 meg link, and it shouldn't be an issue to run it at 65% as your example states.  Although this link would be a "Single point of failure".  Since the connection is between 2 - 2960's the link would be full duplex, with no issues bursting up to 1G from time to time.

For situation 2, you would want to ensure the etherchannel never gets to more than 50% max (meaning never over 1G).  If it's running over 1G on average, you will drop traffic during a link failure.

Dan

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New Member

Re: Recommended maximum ethernet link utilization

Any idea?

Bronze

Re: Recommended maximum ethernet link utilization

Well, it depends.  There is no limit, except the link speed.  But it depends on many other factors:

1. What kind of traffic is running on the link?

2. If it's an etherchannel, and a link fails, will the remaining links be over-subscribed?

3. What is the capacity of the chassis/line card that terminates the interface?

4. If the link is at 100% and your dropping traffic do you care? (meaning, are you prioritizing traffic that needs to get through and dropping traffic that is considered scavenger)?  If someone is running p2p software will it interfere with Voice or production traffic?

For example, if you have an etherchannel with 4 x 1G links, and your running all 4 links at 80% and one link fails, you will be over subscribed on the 3 remaining links.  This also depends on the chassis, since on the 6500, if you lose 1 or the 4 links, all of the traffic from the lost link will be moved to the first link in the bundle, and will carry twice the load of the other remaining 2.

Can you clarify what chassis/line cards your referring to, then we might be able to clarify further.

Dan

New Member

Re: Recommended maximum ethernet link utilization

Thank you Danrya for your comments. I am thinking about 2 different situations:

1) Just one switch, let´s say 2960, connected to other 2960 through a single ethernet link, let´s say Gigabit Ethernet or Fast Ethernet. Let´s assume any kind of traffic, just the total bit rate used, what percentage should I leave free of user traffic on the link for internal network traffic, headers and so? For example, is it OK that all my traffic to be 60Mbps on a 100Mbps link or should I put less user traffic on that link?

2) The other situation is that I have 2 switches 6500 forming a VSS. I create Multichassis Etherlink Channels from 3750 switches, for example 1 Gigabit Ethernet to one 6500 chassis and other 1 Gigabit Ethernet to the other 6500 chasis, thus having 2 Gbps ethernet links. What user traffic should I use as maximum thinking that I cannot drop any traffic if one of the links fails?

Thank you.

Agustin

Bronze

Re: Recommended maximum ethernet link utilization

For situation 1, the 2960 can handle the 100/1000 meg link, and it shouldn't be an issue to run it at 65% as your example states.  Although this link would be a "Single point of failure".  Since the connection is between 2 - 2960's the link would be full duplex, with no issues bursting up to 1G from time to time.

For situation 2, you would want to ensure the etherchannel never gets to more than 50% max (meaning never over 1G).  If it's running over 1G on average, you will drop traffic during a link failure.

Dan

New Member

Re: Recommended maximum ethernet link utilization

Thank you danrya, one last question:

For situation 1, if 65% is not an issue, when should I be alarmed? 70% of user bandwidth utilization? maybe 80%? is there any best practice or recommendation by Cisco?

Best regards.

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