For example, suppose that the XYZ Corporation was previously
connected only to the NorthSouthNet regional. The XYZ Corporation
therefore went off to the NorthSouthNet administration and got an
IP address prefix assignment based on the IP address prefix value
assigned to the NorthSouthNet regional. However, for a variety of
reasons, the XYZ Corporation decided to terminate its association
with the NorthSouthNet, and instead connect directly to the
NewCommercialNet public data network. Thus the XYZ Corporation now
has a new address assignment under the IP address prefix assigned
to the NewCommercialNet. The old address for the XYZ Corporation
would seem to imply that traffic for the XYZ Corporation should be
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routed to the NorthSouthNet, which no longer has any direct
connection with XYZ Corporation.
If the old TRD (NorthSouthNet) and the new TRD (NewCommercialNet)
are adjacent and cooperative, then this transition is easy to
accomplish. In this case, packets routed to the XYZ Corporation
using the old address assignment could be routed to the
NorthSouthNet, which would directly forward them to the
NewCommercialNet, which would in turn forward them to XYZ
Corporation. In this case only NorthSouthNet and NewCommercialNet
need be aware of the fact that the old address refers to a
destination which is no longer directly attached to NorthSouthNet.
If the old TRD and the new TRD are not adjacent, then the
situation is a bit more complex, but there are still several
possible ways to forward traffic correctly.
If the old TRD and the new TRD are themselves connected by other
cooperative transit routing domains, then these intermediate
domains may agree to forward traffic for XYZ correctly. For
example, suppose that NorthSouthNet and NewCommercialNet are not
directly connected, but that they are both directly connected to
the BBNet backbone. In this case, all three of NorthSouthNet,
NewCommercialNet, and the BBNet backbone would need to maintain a
special entry for XYZ corporation so that traffic to XYZ using the
old address allocation would be forwarded via NewCommercialNet.
However, other routing domains would not need to be aware of the
new location for XYZ Corporation.
Suppose that the old TRD and the new TRD are separated by a non-
cooperative routing domain, or by a long path of routing domains.
In this case, the old TRD could encapsulate traffic to XYZ
Corporation in order to deliver such packets to the correct
backbone.
Also, those locations which do a significant amount of business
with XYZ Corporation could have a specific entry in their routing
tables added to ensure optimal routing of packets to XYZ. For
example, suppose that another commercial backbone
"OldCommercialNet" has a large number of customers which exchange
traffic with XYZ Corporation, and that this third TRD is directly
connected to both NorthSouthNet and NewCommercialNet. In this case
OldCommercialNet will continue to have a single entry in its
routing tables for other traffic destined for NorthSouthNet, but
may choose to add one additional (more specific) entry to ensure
that packets sent to XYZ Corporation's old address are routed
correctly.
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Whichever method is used to ease address transition, the goal is
that knowledge relating XYZ to its old address that is held
throughout the global internet would eventually be replaced with
the new information. It is reasonable to expect this to take
weeks or months and will be accomplished through the distributed
directory system. Discussion of the directory, along with other
address transition techniques such as automatically informing the
source of a changed address, are outside the scope of this paper.
Another significant transition difficulty is the establishment of
appropriate addressing authorities. In order not to delay the
deployment of this addressing scheme, if no authority has been
created at an appropriate level, a higher level authority may
allocated addresses instead of the lower level authority. For
example, suppose that the continental authority has been allocated
a portion of the address space and that the service providers
present on that continent are clear, but have not yet established
their addressing authority. The continental authority may foresee
(possibly with information from the provider) that the provider
will eventually create an authority. The continental authority
may then act on behalf of that provider until the provider is
prepared to assume its addressing authority duties.
Finally, it is important to emphasize, that a change of addresses
due to changes in topology is not mandated by this document. The
continental level addressing hierarchy, as discussed in Section
5.7, is intended to handle the aggregation of reachability
information in the cases where addresses do not directly reflect
the connectivity between providers and subscribers.
5.9 Interaction with Policy Routing
We assume that any inter-domain routing protocol will have
difficulty trying to aggregate multiple destinations with
dissimilar policies. At the same time, the ability to aggregate
routing information while not violating routing policies is
essential. Therefore, we suggest that address allocation
authorities attempt to allocate addresses so that aggregates of
destinations with similar policies can be easily formed.