From: Arun Arumuganainar (aarumuga@hotmail.com)
Date: Sun Aug 07 2005 - 03:09:01 GMT-3
Planning a redundancy is tricky task ... ! A Best design will have to
provide maximum link utilization with compromising Redundancy !!!
In this processes we should assume that failure happens very rarely ( Haa
haa if it fails very frequently than we will not buy the product in the
first place ) !!! Hence our objective is to maximize link utilization during
"NO-FAILURE PERIODS " without compromising redundancy when failure actually
happens .When we achieve that , than the total average link utilization over
longer duration will be maximum!!!
Let me explain
Communication can fail due to couple of reason
1) Your Physical layer goes down : Ex : Cable Problem , Problems in the SP
side etc .
2) Your Router or Switch itself is goes down .
Your entire design will have to revolve around how you want to provide
redundancy .i.e whether you care for Line Failures alone (or) both Line &
switch Failures .
Better Design fro Line Failures .
~~~~~~~~~~~~~~~~~~~~~~`
Here You have constraints in investing on the second router or switch ( More
optimistic view ..you trust your hardware and believe that it will never
fail ). Hence you worry only about point 1 . In such a case a single Port
Channel and include all the lines with in the same port channel . In this
scheme you utilization will be maximum as all the available bandwidth will
be utilized . In this case redundancy will be maximum . Communication will
not interrupted until 3 line failures .
Pls, Note : Port channel is logical interface . Hence it will not go down
until switch goes down or rebooted . Since don't care about the switch going
down we need not worry about protchannel going down .
Hence Single port channel with all the four links put under it is best
design in our case !!!!
Better Design for Link and switch failures !!!
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Here you have enough money to invest in additional Switch . In such a case
configure HSRP on the Lan side of the switch . On the Trunk side you can do
the following
1) Configure one switch as Primary( With higher HSRP Priority for the LAN
ports ) include a portchannel for it and make 3 links as it member
2) Configure second one as standby and include 1 link to its portchannel .
This way link utilization will be maximum !!! During normal situation only
one link will be unused .
Still better design is to use GLBP . And configure two routers with one port
channel each and link two links to each portchannel . The link utilization
in this case as good as single router scheme and still you can achieve
router redundancy as good as HSRP scheme.
Hope this helps
Thanks and Regards
Arun
----- Original Message -----
From: "joshua lauer" <jslauer@hotmail.com>
To: "Larry Letterman (lletterm)" <lletterm@cisco.com>;
<chon_mon@nym.hush.com>; <ccielab@groupstudy.com>
Sent: Sunday, August 07, 2005 5:36 AM
Subject: Re: Real World Etherchannel
> We have two bundles of 4 connecting our main campus to a secondary
building,
> and have a 1gb laser to back them both up but we are the govt and we are
> anal so what I can I say :) I think one bundle of 4 is fine, bottom line
is
> how redundant do you really need to be and how much redundancy can you
> afford?
>
> JL
>
>
>
>
> ----- Original Message -----
> From: "Larry Letterman (lletterm)" <lletterm@cisco.com>
> To: <chon_mon@nym.hush.com>; <ccielab@groupstudy.com>
> Sent: Saturday, August 06, 2005 7:46 PM
> Subject: RE: Real World Etherchannel
>
>
> >I think two or more links in one etherchannel is good..
> > We run ours that way..
> >
> >
> >
> > Larry Letterman
> > INS-NW-WEST
> > Cisco Systems
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> > chon_mon@nym.hush.com
> > Sent: Saturday, August 06, 2005 3:52 PM
> > To: ccielab@groupstudy.com
> > Subject: OT: Real World Etherchannel
> >
> > After configuring Etherchannel between switches, is it common practice
> > to have a backup solution if Etherchannel goes down? For example having
> > two Etherchannels, one with a higher priority than the other? Or is it
> > suffice to say that with several links bundled together, that is enough
> > for redundancy.
> >
> > Thanks,
> > Sean
> >
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