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Bandwidth/Throughput & EtherChannels

I am going through the CCNP Switch and I have a question that a CCIE (almost) and I are stuck on:

If Gigabit Ethernet ports are bundled into a single EtherChannel, what is the maximum throughput that can be achieved from one switch to another?

I thought the answer is 8Gbps, but the book says that the answer is 16Gbps. (1 bundle of 8 EtherChannel links) The CCIE (almost) is saying it is 8Gbps too because the throughput is only one way on a link and not both ways (not taking full duplex into account). Although if you take full duplex into account (1Gbps one way and 1Gbps the other) then is it 16Gbps? The link would be 16Gbps because 1Gbps is one way and 1Gbps the other. But the port can only handle 1Gbps, so it really 16Gbps or only 8Gbps?

In this link the author says:

A maximum of 8 active ports are supported in a single EtherChannel. If the ports are operating in full duplex, the maximum theoretical bandwidth supported is as follows:

* Fast Ethernet – 1600 Mbps
* Gigabit Ethernet – 16 Gbps
* 10 Gigabit Ethernet – 160 Gbps

Which gives me supporting evidence for the answer being 16Gbps, but I am not entirely sure, could someone clarify the maximum throughput/bandwidth of an EtherChannel bundle, 8Gbps or 16Gbps?

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Accepted Solutions

Joseph W. Doherty
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Hall of Fame Master

The short answer, the 16 Gbps is the total available aggregate bandwidth for an 8 gig (duplex) link Etherchannel, although on such an Etherchannel the best bandwidth a single flow might achieve from host A to host B would be gig.

When FE and duplex first came out, Cisco (sales?) liked to say individual links had 200 Mbps of bandwidth, this to make them seem twice as good as FE half duplex links.

Although, of course, with duplex there is 100 Mbps in each direction, for a single data transfer, from host A to host B, maximum throughput is still 100 Mbps.  I.e. in theory, no faster than half duplex unless there's also host B to host A traffic too.

I.e. Cisco (sales?) seemed to preferred saying it was 200 Mbps rather than 100 Mbps full duplex.  I suspect this may have been done because it sounded better.

Cisco, though, is occasionally inconsistent on how to describe duplex bandwidth (read up on the 6500 bus bandwidth, it's usually referenced as 32 Mbps, but occasionally it's referenced as 16 Mbps [I believe it's actaully 16 Mbps duplex]), but Cisco still most often doubles the bandwidth for duplex "infrastructure" links, such as when referring to Etherchannel, 3K stack ring or fabric bandwidths.

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5 Replies 5

Mark Malone

Usually when you take into account throughput like that you would take the full duplex from my opinion and experience that's what we have always done it by , so I would agree with you 16gb in general as theory  , but more importantly you need to make sure your load balancing is working correctly on the etherchannel or you will just end up swamping some of the links as it could all be pushed up and down 1 member