Re: [armd] review of draft-ietf-armd-problem-statement-02

[Thomas Narten <[e-mail]>]

Hi Lucy.

Thanks for the review. I've made all your changes, except:

> >   Broadcast Domain:  The set of all links, repeaters, and switches that
>       are traversed in order to reach all nodes that are members of a
>       given L2 domain.  For example, when sending a broadcast packet on
>       a VLAN, the domain would include all the links and switches that
>       the packet traverses when broadcast traffic is sent.

> Comment: in DC, will a link or switch be physical link or virtual
>  link, physical switch or virtual switch? It is better to state
>  explicitly.

I'm not sure we need say whether a link is physical or virtual. I'm
inclined to leave the definition as is. How would it make a
difference?

> > That is, split large L2 networks into multiple smaller L2 networks,
>    each operating as its own L3/IP subnet.  Numerous data center
>    networks have been designed with this principle, e.g., with each rack
>    placed within its own L3 IP subnet.  By doing so, the broadcast
>    domain (and address resolution) is confined to one Top of Rack
>    switch, which works well from a scaling perspective.  Unfortunately,
>    this conflicts in some ways with the current trend towards dynamic
>    work load shifting in data centers and increased virtualization as
>    discussed below.

> Comment: In DC, split large L2 network into multiple smaller L2 network is 
> for security trust design. Multiple L2 networks are on the same L3
> subnetwork so they all can support the same application, but they
> are isolated by L2 network for security reason, which also reduces
> ARP issue.

Agreed. But do we need to say that in the document? (by saying
"comment", I assume you are not asking for text changes.) There are
lots of factors for any particular design choice, and we can't really
describe them all. So I'm inclined to only list those most related to
address resolution.

> >  First, it uses broadcast, and any network with a large number of
>    attached hosts will see a correspondingly large amount of broadcast ARP 
> traffic.
> Comment: it is not necessary true. A lot of trust designs prevent from host
> -to-host communications.

I think the same comment applies here as above.

One thing I note is that using terms like "any network" or "L2
network" is not very precise. To be precise, we often need to be
talking about an L2 domain, i.e, a specific VLAN.

Thanks!

Thomas