v6 & DSL / Cable modems

Owen DeLong owen at delong.com
Fri Feb 6 16:01:55 CST 2009


On Feb 6, 2009, at 12:37 PM, Jack Bates wrote:

> David W. Hankins wrote:
>> What most people do of course is VRRP.
>
> I agree, and I have done this in the past. However, I am very happy  
> with the support of IPv6 to do away with requiring VRRP.
>
If RA does that in your situation, great.

In my situation, there are actually cases where I need different VRRP  
groups on the same
LAN and need to point different things at different routers from hosts.

It would be nice if DHCPv6 (or DHCPv4 for that matter) could include  
not only a default,
but, a static routing table in what it distributes.

Nonetheless, the built in assumption in IPv6 RA that all routers are  
equal is simply
not valid in all environments and VRRP with DHCP provides some ability  
to cope
in environments where that isn't true.

>> Barring that, you just specify multiple default routers, and the
>> client will select the router that still responds to ARP.  But
>> support for this is not universal, so.
>
> Always a problem, though arp doesn't timeout when a end node  
> disappears in a reasonable fashion.
>
Some OS handle this better than others.
Try, wait, try, wait, re-arp, wait, fall over to other gateway -- 9  
sec. delay in some situations.

>> When that isn't available, what I have done in the past here is to  
>> use
>> the DHCP server to give out a default router option that is sorted
>> according to the DHCP relay agent that was used to reach the server
>> (keyed on giaddr contents).
>
> This is a nice method as well, though limited by the half life of  
> the DHCP lease. It also doesn't address the fact that you might be  
> handing out IP addresses from *both* DHCP relay agents with cross  
> redundancy for gateways.
>
I'm not sure what you mean by that.

>> No need to take on 'routed -q' in the client, it can stay a simple
>> dumb host, with all configuration complexity in the DHCP server or
>> negotiated in HA by the routers.
>
> Dumb hosts is exactly what makes life infuriating. I want smart  
> hosts. The network should be relatively dumb. Perhaps I'm mistaken,  
> but the premise of IP was that hosts are smart and networks are  
> dumb. Then we started making smart networks to break things.
>
That's great on paper, but, in some real world scenarios, it's not as
supportable as one might want.

The best thing is if both are smart in helpful ways and are willing to
be told not to out-smart themselves in environments where that is
counterproductive.

> I want built in multiple IP bindings on my hosts. I'd like (Windows  
> 7 without having to call netsh, perhaps?) support for static and  
> dynamic addresses (privacy extensions are beautiful). I especially  
> want support for multiple dynamic addresses with communication to  
> the host that it should start using a newer address for future  
> requests, yet finish up what it's doing with the old address before  
> unbonding it.
>
Could you please explain a good reliable method for source address  
selection in a multiple IP binding scenario?

That last one is available albeit really hard to support in any sort  
of scale.

> Please don't get me wrong. I don't run a corporate network. I have  
> my own little server farm and I have support to edge customers. What  
> customer's do with the prefixes I give them is up to them. DHCP/ 
> SLAAC, it's all good. I'd rather not run DHCP for my servers or my  
> little helpdesk network. On a standard ISP edge, I expect to see  
> hybrid solutions; depending on the layout.
>
I don't know very many people who want DHCP for servers.  However,  
when you're managing a bunch
of user's desktops and laptops, DHCP is the only way to scale things  
reasonably in some environments.

Owen





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