Proposed change at the Interconnect

epg epg
Mon Nov 2 22:26:04 UTC 1992

The T1 backbone and the T3 backbone have provided a backup path to
mid-level networks which peered with both backbones. 

                               / \
                              /   \
                     +------+      +------+
                     |      |      |      |
                     |  T1  |------| T3   |
                     |      |      |      |
                     +------+      +------+
                    /     \          /     \
                   /       \        /       \
                 a          \      /         \
                             \ y  /           b

This was done by announcing all known networks from one backbone
to the other via the interconnection between the two. One of the
benefits of doing this was that it provided a transition from the
T1 backbone to the deployment of the T3 backbone.

Now that almost all of the peers that were known to the T1 are
also known directly to the T3 and the T3 has implemented 
backup plans in addition to the T1 backbone, we would like to
stop announcing the networks associated with dual homed peers
from the T3 to the T1. This means that T1 only networks will
no longer have a backup path through the T3 if a dual homed site
loses its connectivity to the T1 backbone.

In this proposed configuration, at the interconnection, the
T1 will announce networks a, x and y to the T3.  At the interconnection,
the T3 will announce network b to the T1. This plan will have the
following affect:

1)  if the connection between x and the T1 breaks,

b will reach x via the T3
y will reach x via the T3
a will find x unreachable 


2)  if the connection between x and the T3 breaks,

b will reach x via the interconnect to the T1 
y will reach x via the interconnect with the return path via the T1
a will reach x via the T1

CA*net and EASInet are the only peers which remain T1 only.  We have
contacted them previously concerning this proposal and they are
aware of the proposed change.  We are also in the process of working with
those two organizations to convert them to the T3 backbone.

We would like to make this configuration change by the end of this
week, November 6, 1992. This step will help to maintain the T1
backbone until the remaining peers have transitioned to the T3
by reducing the amount of routing information that the RTs need
to assimilate.  It is also another step in preparation to
the eventual dismantlement of the T1 backbone.

If you have any questions concerning this proposal
please notify us as soon as possible.

Thank you.

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