From: Waters, Kivas (UK72) (Kivas.Waters@xxxxxxxxxxxxx)
Date: Fri Dec 07 2001 - 12:37:56 GMT-3
Hi Glenn, my opinion is that a layer 3 design is much better than a layer 2
design. I much prefer to troubleshoot a L3 network than a L2 design.
Using HSRP gives you much faster convergence times than SPT at L2, even in
the light of Cisco's backbone fast etc. Saying this I have seen problems
with HSRP in certain situations such as multicasting etc. Using a
layer-3-only design also limits the assignment of VLAN's and VLAN
flexibility.
Layer 2 spanning tree operation can suffer from broadcast storms not
allowing BPDU's to get across a link, causing havoc. Convergence is slow
and the utilisation of redundant links is not an option.
There are more advantages/disadvantages but at the end of the day I try to
design and impliment new switched networks which do not include any layer 2
loops at all. With MLS and IP CEF, in my opinion there is no longer a
strong case for a super fast L2 design in the core.
regards
Ki
-----Original Message-----
From: Williams, Glenn [mailto:WILLIAMSG@PANASONIC.COM]
Sent: 07 December 2001 14:51
To: 'Larson, Chris (Contractor)'; 'ccielab@groupstudy.com'
Subject: RE: Layer 2 Redundancy
Well, I guess, a little off the well designed network, (grin) I was thinking
a distribution layer designed layer 2 vs.. layer 3.
GW
-----Original Message-----
From: Larson, Chris (Contractor) [mailto:Chris.Larson@ed.gov]
Sent: Friday, December 07, 2001 8:38 AM
To: 'Williams, Glenn'; 'ccielab@groupstudy.com'
Subject: RE: Layer 2 Redundancy
Actually I have not heard that argument. It depends on what you are doing
and the requirements. We have a 6 switch layer 2 core that feeds our Layer 3
distribution switches and our L3 distribution swiches have layer 2
redundancy with our access switches but run HSRP to provide L3 redundancy to
the stations hanging of the layer 2 closet access switches.
I have never heard arguments against layer 2 redundancy. I believe in a well
designed high reliable network from end to end you would need a combination
of both layer 2 and layer 3 redundancy and they go hand in hand to produce a
healthy, available and efficient network
-----Original Message-----
From: Williams, Glenn [ mailto:WILLIAMSG@PANASONIC.COM
<mailto:WILLIAMSG@PANASONIC.COM> ]
Sent: Friday, December 07, 2001 8:52 AM
To: 'ccielab@groupstudy.com'
Subject: Layer 2 Redundancy
Hi,
Is the major argument against layer 2 redundancy (vs. layer 3 & HSRP) the
potential for layer 2 loops and problems with spanning tree. So I take it
layer 3 is the best way to go in the industry.
Thanks
GW
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