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Teaming (LAG) swtich ports across non-stacked switches

Posted on 2008-06-19
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Last Modified: 2008-06-21
Is it possible to LAG or Team switch ports across switches that are not stacked or even stackable?  I say no, that it's not possible even using LACP, but I have a client that believes that it is possible.  

The specific switches in question are the Dell 5424 (a L2 managed switch).  Tech specs link here:
http://www.dell.com/content/products/productdetails.aspx/pwcnt_5424?c=us&cs=04&l=en&s=bsd
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Question by:pwyzorski
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by:kdearing
kdearing earned 100 total points
ID: 21827088
Yes, you can.

You can use it to increase bandwidth between 2 devices, or to connect to redundant switches, etc.
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by:pwyzorski
ID: 21827706
Yes, I understand the utility of Link Aggregation well enough.

My question was more to the point of how to setup Link Aggregation across non-aggregate switches.  What is the protocol that determines what port on which switch gets used for downlink traffic.  Is it LACP? Static or Dynamic mode?

The protocol to determine which uplink port on aggregate NICs to use for upstream traffic from the host is simple enough to understand.  It's the downlink trip from the network back to the host that confuses me.

I think that the LACP protocol is used to determine a dynamic route and downlink port downstream to the host even across non-aggregate switches. But can LACP be used in static mode to determine a route across non-aggregate switches.
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by:kdearing
kdearing earned 100 total points
ID: 21828364
Enen though 802.3ad is supposed to be a standard, many maunfacturers have implemented their own flavor with 'enhancements' (especially Cisco).

I've set up some Nortel switches and they have a 802.3ad extension called Split Multi Link Trunking.
This allows two aggregation switches to appear as a single device to edge switches that are dual homed to the aggregation switches.

I'm not sure if those specific Dell switches have similar capabilities.
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by:
from_exp earned 400 total points
ID: 21828560
hi!
Teaming can have different types of behavior: aggregated and redundant.
when the first one is generic link aggregation based on 802.3ad, the second use the second card only when the first one fails.

as for switches I haven't seen switches save Nortels where it is possible to use aggregated mode in non-stacked configuration. however it is always possible to use redundant mode with non-stacked switches, where from the switches' perspective you have only two normal ports going to the same server.
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by:pwyzorski
ID: 21828649
I read about SMLT in Nortel switches, but that isn't what I have.  I'm more curious about how it's supposed to work in a general sense.
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by:pwyzorski
ID: 21828659
"however it is always possible to use redundant mode with non-stacked switches, where from the switches' perspective you have only two normal ports going to the same server."

That statement does not make sense to me.  I thought this to be a routing issue where one switch or the other is chosen as a downlink pathway by a router.  How can a switch know about another switch in a non-aggregated configuration?  Unless you think I'm talking about LAG on a single switch, but I'm not.  The LAG is actually spanned across two non-aggregated switches.
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Author Comment

by:pwyzorski
ID: 21828660
Thanks for the responses, but I'm still looking...
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LVL 21

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by:from_exp
from_exp earned 400 total points
ID: 21828686
no, a bit different
in redundant mode, only server has teaming configuration and only one NIC is active at a time, so you don't need to configured lag on switches.
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by:pwyzorski
ID: 21834571
So with the NICs on the host aggregated and no LAG configuration on the switches what we end up with is simple redundancy.  I can get that.

What protocol or protocol aspect defines what switch gets used during a failure event with the primary switch.  Assume simplest scenario with a single router and two switches with multiple hosts connected to both switches.  Is this situation sorted out simply by normal dynamic routing algos?
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by:from_exp
from_exp earned 400 total points
ID: 21834749
I would say you even don't need dynamic routing.
static failover only.
so if you have two switches (connected via LAG, without stack) so you can connect each server to both of them having NICs in redundant LAGs and multiple routers connected each to the appropriate switch. two routers then have vrrp (or cisco's hsrp) running to provide gateway redundancy to PCs
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by:pwyzorski
ID: 21834991
How about a single router connected to both switches?
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by:kdearing
ID: 21835135
Extreme devices have ESRP which is similar to VRRP/HSRP but also works on their layer 2 switches.
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LVL 21

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by:from_exp
from_exp earned 400 total points
ID: 21837061
possible, to do that also, but how would you like to arrage failover?
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Author Comment

by:pwyzorski
ID: 21838414
some reason client isn't opting for failover at the router level... beats me...

I'm done one this, thanks for the help. I'll award points between you two as such:
'from_exp' - 400pts
'kdearing' - 100pts

thanks
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