From: Mike Williams (ccie2be@swbell.net)
Date: Sun Nov 02 2003 - 21:21:36 GMT-3
Howard,
Actually, Cisco does distiguish between L2 and L3 etherchannels:
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat6000/ios127xe/con
fig/channel.htm
Having said that, it boils down to this: A L3 Etherchannel has an IP
address configured on it's port-channel interface. So basically, aside
from the engineering putting an IP address on it and "treating" it as
L3, it's the exact same thing as a L2 etherchannel...... So I don't
think it's "marketingspeak" as much as simply using a term to describe
the "mode" of use of a given etherchannel bundle.
You bring up a good point not to confuse this with the IOS functionality
that will load balance over routes it considers equal (whether learned
dynamically or from static routes, etc). However, the load-balancing
we're speaking of (as I'm sure you well know) is specific to an
etherchannel bundle, and can be based on A) dest. MAC, B) source AND
dest MAC, C) dest IP, or D) source AND dest IP (note* when I say "AND"
here, it's really an XOR operation performed on the source and dest
MAC/IP addresses to determine which link in an etherchannel bundle is
taken). So it's clear that etherchannels (whether being used as a pure
L2 link or as an L3 link) can use Layer 3 information to determine which
link traffic goes on, but this is separate from the IOS load-balancing
you speak of, correct?
I see your point, tho, that using terms like L2 and L3 etherchannel
could confuse. I gave an example where we have a etherchannel link
between a 7500 and 6500 where the 7500 side has an IP (and would be
called an L3 etherchannel) and the 6500 side doesn't (and would be
called an L2 etherchannel). This shows that you don't even have to have
both ends of an etherchanel configured the same (as far as being L2 or
L3).
Mike W.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Howard C. Berkowitz
Sent: Sunday, November 02, 2003 8:36 AM
To: ccielab@groupstudy.com
Subject: RE: Dumb Question but will ask
I'm confused. Has Cisco, somewhere, actually defined L3 EtherChannel?
If it has, it's yet another case of marketingspeak, creating
meaningless concepts such as L3 vs. L2 switches.
If it hasn't, and we are speaking of load distribution based on L3
information, we are speaking of a normal IOS function. Let me repeat:
load sharing has nothing to do with the routing protocol. You can
load share among static routes.
At 8:26 AM -0600 11/2/03, Mike Williams wrote:
>If I'm not mistaken, you can use the source IP and dest IP addresses to
>determine which link in a L2 etherchannel that traffic will take. So
>even if you have a L2 etherchanenl between 2 routers, the traffic can
>balance over the links (in proportion to the distribution of the
>source/dest addresses).
>
>Mike W.
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>Ryan Cheng
>Sent: Sunday, November 02, 2003 1:25 AM
>To: Shafi, Shahid; ccielab@groupstudy.com
>Subject: Re: Dumb Question but will ask
>
>
>Hi Shahid,
>
>Etherchannel is to make 2 or many physical links to be a logical link,
>but the question comes, how to load-share the traffic into each link?
>
>L2 Ethernet: it makes use of the L2 information (e.g. Ethernet DA and
>SA) as a matching criteria, says any traffic which has a different DA
>and SA in the ethernet header will be flowed into different physical
>link
>
>L3 Ethernet: in contrast, the L3 information (e.g. destination and
>source IP
>address) is used in this case
>
>If you are using a L2 ethernet channel between Routers, the
>load-sharing won't work since all traffic between the routers have a
>fixed Ethernet DA and SA.
>
>Hope my reply is useful.
>
>Regards,
>Ryan
>
>----- Original Message -----
>From: "Shafi, Shahid" <sshafi@qualcomm.com>
>To: <ccielab@groupstudy.com>
>Sent: Sunday, November 02, 2003 8:40 AM
>Subject: Dumb Question but will ask
>
>
>> Hi Guys,
>>
>> A stupid one but I'll ask though I think I know the answer: What is
>> the difference between layer2 and layer 3 etherchannel? What wont
>> work
>
>> if I use Layer 3 Etherchannel between switches? VTP?? What is more
>> efficient and why?
>>
>> Any input is great!
>>
>> thanks
>>
>> Shahid
>>
>>
>>
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