Re: [load balancing] Layer 2 path vs Layer 3

From: Michael Batchelder (binkyIZZATcertaintysolutions.com)
Date: Fri Oct 13 2000 - 17:57:39 EDT


tony bourke wrote:
>
> Has anybody here had any experience iwth this debate?

Yes.

> There are three ways to get the packets to get rewritten after leaving the
> server:
>
> Bridging-path: When the return packets traverse the load balancer by
> being in the Layer 2 path. This is how the switches usually work, as well
> as the localdirectors.
>
> Routing-path: When the return packets traverse the load balancer by being
> in the Layer 3 path, the servers have the load balancer as their default
> route. This is how devices such as F5's BIG-IP work, as well as most of
> the other server-based units. Most of the switches can operate this way,
> as well.
>
> Direct Server Return: This is where the server re-writes the packet
> itself by implementing some ip/arp trickery.
>
> I prefer using the layer 3 routing-path method, since layer 3 redundancy
> is better than spanning tree. It also eleminates briding-loops and
> such. Anyone else have a comment on that?

Disclaimer: I've only done this with Alteons. Just starting to work
w/LD and so far I find them annoying and limited.

I prefer your method (layer 3). I don't like having my topology
complicated by having a l-b switch on top of a regular one. Don't like
my redundancy relying on spanning tree rearranging my topology on the
fly. The Alteon limitation of 1 spanning tree domain per box is
annoying. I'd rather have chatty multicast from VRRP than ethernet
Spamming Tree broadcasts, though that's not based on anything
hard/objective.

Having said that, my company's networking gods prefer the layer 2
method. I believe this is because they don't like/trust anything that
routes and does stuff like VRRP if it's not a Cisco. Also, I think they
don't want to take a fast box and make it do slower stuff (IP
forwarding). Eh... Every Alteon I've ever seen has never broken a
sweat in it's life...

What's in the third category? Resonate?

Michael



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