RA & DHCP problem...

[Nick Hilliard]

On 30/12/2013 11:31, Mikael Abrahamsson wrote:
> Why would one want to build huge L2 domains? It's a lot of pain, and there
> is no address limitation that means you "must" do this.
> 
> What's the use-case that requires large L2 domains as the "best" solution?
> And on top of that, that requires different hosts within this L2 domain to
> have different default gateways?

This is a different issue and slightly unrelated to the issue of RAs and
DHCPv6, but as you asked there are two conflicting problems here: if you
have large l2 domains, you run into problems with implementing RA guard and
dhcpv6 guard at the customer edge but in general routers cope better with
this scenario.  If you have one l2 domain per customer, you run into
problems with routers generating sets of VRRP/whatevs packets per customer,
but you have no issues with rogue RAs/DHCPv6 because the customer will only
hurt themselves.  This isn't a problem which will affect smaller networks,
but if you scale up to thousands of customers, many routers will not handle
the VRRP requirements for that many l2 domains.  You could use larger
numbers of smaller routers, but then you lose economy of scale.

Nick