The IP over ATM Mailing List Archive by date

[manfredi@engr05.comsys.rockwell.com (Albert E. Manfredi)]

If we start with the existing interconnected Internet, is it difficult to 
add a huge, ATM-based IP flatnet to the Internet? I wouldn't think so, 
unless we worry about efficient routing _through_ this flatnet.

PREMISES

The premise here is that the legacy IP nets are all interconnected via 
current means (dedicated lines and routers). The IP-ATM flatnet (flat with 
respect to IP only) is connected to the legacy Internet via any number of 
routers at the edge. These edge routers, to keep things simple, do _not_ 
advertize connectivity to other IP nets; only to the one huge flatnet.
Also, each ATM host and edge router is configured with the ATM address of
its DNS and ARP server.

INBOUND TRAFFIC

IP datagrams from legacy Internet networks destined to the IP-ATM flatnet
find their way to the closest router connecting to the ATM medium, using 
normal routing algorithms. The closest _edge router_, not necessarily the 
shortest path to the destination host.

The edge router queries its ARP server to find the ATM address of this 
IP-ATM destination host. (These ARP servers must periodically transmit 
their ARP tables to the other ARP servers and must cache the ARP tables 
for this IP flatnet.)

Then the IP datagrams are routed to the ATM destination efficiently by
the PNNI or public NNI.

OUTBOUND TRAFFIC

The ATM network has to provide a DNS and ARP-like service.

If an ATM host wants to open a session with another ATM host on the same 
IP flatnet, the DNS will provide the ATM address of that other ATM host.
The NNI takes care of routing.

If an ATM host wants to communicate with a legacy IP host, the ATM-DNS
query results in the ATM address of one (or more, for reliability) router 
which is, for simplicity, the closest to that DNS server.

Note that this DNS server can easily provide the minimal ARP function 
required of it. Edge routers are not expected to change very often, and 
each server only worries about one or very few edge routers. Also note 
that I didn't make an unamiguous distinction between DNS server and ARP 
server.

TRAFFIC TO OTHER IP-ATM NETS

An IP-ATM net which is not connected to this flatnet looks like a legacy 
IP net to these ATM hosts and servers. If this other IP-ATM net _is_ 
connected to the huge flatnet, then it can simply become part of the same 
IP flatnet.

THROUGH TRAFFIC

Since the ATM edge routers do not advertize routes to other IP nets, in 
this simplest implementation there is no through traffic. This simplest 
scheme can be elaborated on, of course, to allow through traffic. The ATM 
edge routers could communicate IP net reachability information among one 
another, even if the ATM address of each of the other edge routers must be 
statically configured.

Just wanted to show that if we don't worry too much about routing
algorithms to make Mssrs. Ford and Fulkerson proud, we can, I believe,
build a huge and viable IP flatnet over ATM.

Bert
manfredi@engr05.comsys.rockwell.com