Subject: Fwd: DISCUSS: draft-ietf-ipv6-deprecate-site-local

From: Alex Zinin <[email-masked]>
Date: Thu, 18 Mar 2004 01:42:08 -0800

fyi
-- 
Alex
http://www.psg.com/~zinin/

This is a forwarded message
From: Alex Zinin <[email-masked]>
To: [email-masked]
Cc: 
Date: Wednesday, March 17, 2004, 10:33:37 PM
Subject: DISCUSS: draft-ietf-ipv6-deprecate-site-local

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Logged in the tracker:

My general comment here is that I would change the tone of the section from
"this creates problem" to "this increases router implementation and management
complexity". In other words, we could get it to work, we know the mechanisms
for that, but the complexity price is high.

Some rewording suggestions, plus some additional thoughts:

> 2.4   Router pain, routing tables
                     ^^^^^^^^^^^^^^
                     increased complexity

>    The ambiguity of site local addresses also creates problems for the
                                                        ^^^^^^^^
                                                        complications
>    routers. In theory, site local addresses are only used within a
>    contiguous site, and all routers in that site can treat them as if
>    they were not ambiguous. In practice, problem occurs when sites are
                                           ^^^^^^^^^^^^^^
                                           special mechanisms are needed
>    disjoint, or when routers have to handle several sites.

>    In theory, sites should never be disjoint. In practice, if site
>    local addressing is used throughout a large network, some elements
>    of the site will not be directly connected. This will create a
                                               ^
                       + for example, due to network partitioning

>    demand to route the site-local packets across some intermediate
>    network. In practice, this leads to an extensive use of tunneling
            ^
       + (such as the backbone area) that cannot be dedicated for
         a specific site.

>    techniques, or the use of multi-sited routers, or both.
>    
>    Ambiguous addresses have fairly obvious consequences on multi-sited
>    routers. In classic router architecture, the exit interface is a
>    direct function of the destination address, as specified by a single
>    routing table. However, if a router is connected to multiple sites,
>    the routing of site local packets depends on the interface on which
>    the packet arrived. Interfaces have to be associated to sites, and
>    the routing entries for the site local addresses are site-dependent.
>    The route management software and the routing protocols have to
>    account for the site boundaries. This can be particularly hard to do
>    when sites are adjacent or overlap.

Change the last two sentences to:

"Supporting this requires special provisions in routing protocols and techniques
for routing and forwarding table virtualization that are normally used for VPNs.
This contributes to additional complexity of router implementation and
management."

Add:

"Network management complexity is also increased by the fact that though
sites could be supported using existing routing constructs--such as domains
and areas--the factors driving creation and setting the boundaries of sites
are different from the factors driving those of areas and domains."

>    In multi-homed routers, such as for example site border routers, the
>    routing process should be complemented by a filtering process, to
>    guarantee that packets sourced with a site local address never leave
>    the site. This filtering process will in turn interact with the
>    routing of packets, as it may cause the drop of packets sent to a
>    global address, even if that global address happen to belong to the
>    target site.

"routing" should be changed to "forwarding" above.

What does "may cause the drop" mean here? As a result of a bug
or because the algorithm is not predictable?

>    In summary, the ambiguity of site local addresses makes them hard to
>    manage in multi-sited routers, while the requirement to support
>    disjoint sites creates a demand for such routers.
                   ^
               + and existing routing protocol constructs.

--
Alex

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