[c-nsp] Alternatives to 3750 w/ Stackwise?

[Jeff Kell]

On 11/26/2010 10:16 PM, John Elliot wrote:
> >
> > stacked 3750s give you "failover L3 SVIs" by design (provided your
> > uplinks are cross-chassis etherchannel) without the
> > overhead/complications of HSRP, but they are pricey.
> >
> > With the 3750X series, if you stack "more than two" in a real routed
> > (IPServices) stack, the other members must be at least IPBase. They do
> > have a LANbase model that is essentially layer-2 only, but bear in mind
> > (we learned the hard way) that it will NOT stack with the other license
> > models of the 3750/3750E/3750X (it is essentially ignored).
>
> Thanks, so my options are 3750's, and I'll have single management
> across all 3750's implicitly, or 3560's and would need to run
> something like hsrp/GLBP to avoid having to login to both switches to
> make mods?

Cisco "stacks" are managed as single units, the members becoming like
blades of a modular switch.  If you lose a switch, it's much like losing
a blade.  Configurations are duplicated across the members.  If it's
layer-3, SVIs stay up and are virtualized with the master switch.  If
you want to keep it redundant, you need to run cross-chassis
etherchannels where you want redundancy (if one switch goes down, the
channel stays up on the remaining switch[es]). 

For full fancy routing, you'll need two IP Services licensed switches in
the stack (and they should have the uplinks).  Additional switches can
legally be IP Base... and if both your IP Services die, the stack will
reboot as layer 2, and generally create havoc.  If you can afford to
keep them all the same license level, that's the "Cisco Way" and easily
supported -- you can update the image on the master and it is propagated
to the members, etc.   

I started out with a 3750 stack in our server farm, they make great
rack-top switches, and adjacent racks can be stacked with the
appropriate stack cables (although the longest available is 3-meters, so
you can only go so far).  I've since added a 3750E stack in another rack
group.  I'm getting better performance than the older 4500s they
replaced (older 6G-per-blade SupIVs).  You can get wire-speed 4900s, but
that only gets you the 48 ports before you bottleneck to an uplink.

The only downsides I've recognized are:

* There is really no "minimal interruption" maintenance option for
software upgrades.  You can't do a failover / update / fail-back style
rolling upgrade.  Differing IOS versions across the stack will result in
a reload and another master election.

* They take FOREVER to boot (in the order of five minutes...) during
which time the WHOLE STACK is unresponsive.

* If you're really pushing the redundancy factor, they have a current
limitation of 48 port-channels per stack.

* They're still pricey (3750Xs are better)

Jeff