Re: arp table - same mac address shows two ip addresses

Hi,

On Thu, Oct 18, 2018 at 09:16:12AM -0600, Grant Taylor wrote:
> On 10/18/2018 01:10 AM, Erik Auerswald wrote:
> 
> >One example I experienced are misconfigured end-systems using IP
> >addresses from network A in the broadcast domain of network B. The
> >gateway for both networks was based on the Linux kernel.
> >Misconfigured hosts were able to reach their gateway without
> >problems (the ARP request was answered from the "wrong" interface,
> >any interface accepts any IP destined for the host).
> 
> I feel like there are details pertinent to the conversation that I'm
> not privy to.  Including shared or separate broadcast domains,
> routing, IP addressing scheme, etc.  Most of which would need to be
> known from both ends of the communications to be able to even
> speculate.

The original question was a bit scarce on details, thus I substituted
pertinent experience of my own. This is not necessarily easy to follow. ;)

> >AFAIK one can configure ARP to separate more, but not competely.
> >Using bridges is said to allow for more separation, but I have not
> >yet tested this.
> 
> I'm going to be doing some testing in this area, partially around
> this conversation and other very similar conversations.

Please tell us about your results.

> >For version 4, but this changes with version 6. ;-)
> 
> Would you please elaborate?

In IPv6, addresses are assigned to interfaces. This is obvious with
link-local addresses, but true for differently scoped addresses as
well. I am sorry, but I do not know the RFC off the top of my head.

OK, had to search...

RFC 8200, Internet Protocol, Version 6 (IPv6) Specification, section 2:

    "interface    a node's attachment to a link."
    "address      an IPv6-layer identifier for an interface or a set of
                  interfaces."

RFC 4291, IP Version 6 Addressing Architecture, section 2.1:

    "IPv6 addresses of all types are assigned to interfaces, not nodes."

> I've not run across anything indicating such.  I've not gotten far
> enough in the reading that I'm doing to delve this deep into IPv6
> yet.

IPv6 is an interesting rabbit hole to dive into. ;)

> >I'd say the same. But part of the problem is that the weak host
> >model is a bit more surprising than the strong host model. In my
> >experience this is especially true when a weak host is used as a
> >router.
> 
> I assume that the weak host (end system) model is easier to code
> for, thus more likely to be used on single homed hosts (end systems)
> a they are the vast majority compared to multi-homed hosts (E.S.).

They might even be a bit simpler to use without a 100% correct networking
configuration. ;)

> Thank you!  Good discussion that is banging some of my brain cells together.

Likewise. :)

Thanks,
Erik
-- 
I think of math as a splendid way to learn to think straight.
                        -- Bjarne Stroustrup