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Description  |
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TECHNICAL FIELD
This invention relates to the interconnection of local area networks (LANs)
and subportions thereof.
BACKGROUND OF THE INVENTION
The current embedded base of data networks are based on IEEE 802 Local Area
Networks, i.e., so-called "Legacy LANs". These Legacy LANs are so-called
"connectionless" because network entities exchange packets without
establishment of a layer-2 connection. Many existing and emerging
applications are designed to run primarily on Legacy LANs. These
applications reside on top of so-called "layer-2" and "layer-3" protocols
such as Medium Access (MAC) and Internet Protocol (IP), respectively. As
is well known in the art, the layers referred to are those of the
international standards organization (ISO) seven layer networking
reference model.
Asynchronous transfer mode (ATM) with its a) fixed size cell switching, b)
sealability from few megabits to hundreds of megabits, c) ability to offer
guaranteed quality of service (QoS) on a per connection basis, and d)
connection orientation, is viewed as the enabling technology for
high-speed multimedia networking. Therefore, it is desired in the art to
interconnect Legacy LANs and ATM end-stations, to themselves and to each
other, using ATM. This has been achieved in the prior art in a variety of
ways.
To describe the existing solutions, consider the example shown in FIG. 1 of
two small networks 101 and 103, each representing a different logical
subnet at layer-3. LAN 101 has sites 111, 113, and 115 which are
interconnected through an ATM wide area network (WAN) 131. Hosts 111-1,
111-2 and 111-3 of site 111 are connected via Ethernet 111-4, hosts 113-1,
113-2, and 113-3 of site 113 are connected via Ethernet 113-4, and ATM
hosts 115-1 and 115-2 are connected to an ATM switch 115-6 at site 115.
Similarly structured, the second network, LAN 103, has only two hosts per
Ethernet site.
A classical method for interconnecting these sites is so-called "bridging
and routing". Consider the case of host 111-1 sending a data packet to the
MAC address of host 113-2. All stations on Ethernet 111-4, and
consequently, bridge 111-5 receives the packet. Bridge 111-5 a) builds
broadcast ATM connections to bridge 113-5, hosts 115-1 and 115-2; b)
encapsulates host 111-1's data packet on top of the ATM layer, and c)
sends it over the ATM connections.
Bridge 113-5, hosts 115-1 and 115-2 receive the information transmitted
over the respective ATM connections. Bridge 113-5 strips of the ATM
encapsulation, converts the ATM cells into a MAC packet, and sends it to
Ethernet 113-4. Thus, all stations on Ethernet 113-4, and consequently,
host 113-2 receives the data packet. Hosts 115-1 and 115-2 ignore the
received data packet since it is not addressed to them.
lnter-LAN communication according to this technique is achieved through the
use of external router 151, since networks 101 and 103 are in different
layer-3 subnets. For example, if host 117-1 wants to communicate with host
111-1, host 117-1 sends a data packet to the MAC address of router 151, in
which case bridge 117-5 builds an ATM connection to router 151 and sends
an ATM encapsulated data packet thereto. Router 151 forwards the packet to
bridge 111-5.
A deficiency of this method is that, since it is based on a broadcast
principle and thus mimics shared-medium operations, all data packets are
broadcast to all ATM destinations, thereby flooding the network with
broadcast traffic. Another deficiency is that the broadcast nature of the
technique virtually requires a mesh network between all bridges and ATM
hosts within a LAN, and all inter-LAN traffic must pass through router
151.
The ATM Forum has developed another bridging solution called LAN Emulation
(LANE). LANE relies on a LAN Emulation Server (LES), which performs
ATM-to-MAC address resolution, i.e., translation, and a Broadcast and
Unknown Server (BUS), which performs data broadcast. The above-described
example operates in a LANE environment as follows.
LAN 101 and LAN 103 constitute two different ELANs. As shown in FIG. 2, LAN
101 is served by LES 201 and BUS-203 while LAN 103 is served by LES 211
and BUS 213. As in the previous technique, host 111-1 transmits a data
packet with the MAC address of host 113-2. All stations on Ethernet 111-4,
and consequently, bridge 111-5, receive, the data packet. Bridge 111-5
either contains within its own information the ATM address of host 113-2,
or, if not, it establishes an ATM connection to LES 201 and transmits
thereto a so-called "LE.sub.-- ARP.sub.-- request" message to obtain the
ATM address of host 113-2. The LE.sub.-- ARP request is defined in the ATM
Forum's LAN Emulation Over ATM Specifications, Version 1.0, which is
incorporated herein by reference and the contents of which are well known
by those skilled in the art.
If LES 201 contains within its own information the requested address, it
responds by transmitting it to bridge 111-5. Bridge 111-5 then builds an
ATM connection to bridge 113-5, and transmits thereto the data packet.
Otherwise, LES 201 broadcasts an LE.sub.-- ARP.sub.-- Request message
requesting the ATM address of host 113-2 to all other LAN Emulation
Clients (LECs) in ELAN 101, namely bridge 113-5, hosts 115-1 and 115-2.
Generally speaking, LAN emulation clients (LEC) are end-stations or
bridges that are directly connected to an ATM network. Bridge 113-5
responds to LES 201 with its own ATM address, because it is serving host
113-2, the host whose MAC address has been specified. Here, bridge 113-5
is called a "Proxy LEC", since it represents multiple end-point addresses,
e.g., the MAC addresses of hosts 113-1, 113-2, and 113-3. For a more
detailed description of the definitions of LEC and proxy LEC reference may
be made to the above-mentioned ATM Forum's LAN Emulation Over ATM
Specifications, Version 1.0.
Broadcast data packets, such as a so-called "ARP.sub.-- Request", are
forwarded to a BUS, which in turn broadcasts them to all LECs. "ARP.sub.--
Requests" are defined in Bell Communications Research (Bellcore) request
for comments (RFC) 826, which is incorporated herein by reference. Also,
data packets are sent to a BUS until a direct ATM connection is
established to the target address within the LAN.
Similar to the previous example, the communications between two Emulated
LANs is done via external router 151. Bridge 117-5 receives a data packet
from host 117-1 to the MAC address of router 151. Either bridge 117-5 has
the ATM address of router 151, or it requests the address from LES 211.
After obtaining the ATM address of router 151, bridge 117-5 builds an ATM
connection thereto, and transmits the data packet over the connection.
Either router 151 has the ATM address of bridge 111-5, or it requests the
address from LES 201. Router 151 then builds an ATM connection to bridge
111-5, and send thereto the data packet. The data packet will be received
by bridge 111-5 and passed to hosts 111-1, 111-2 and 111-3. Thus,
disadvantageously, all inter-LAN packets must pass through router 151,
which may become a communications bottleneck.
A third method builds upon LANE, but incorporates the routing function as
well as bridging function into a so called multi-layer LAN switch.
Fundamentally, there are three major functions associated with routing: 1)
routing, i.e., determination of the layer-3 address of the next-hop-router
along the path to the target address, 2) address resolution or
translation, i.e. determination of a router's ATM address corresponding to
its layer-3 address, and 3) data forwarding, i.e., relaying data packet
from one port of the router to another port. A traditional router performs
functions (1) and (3) while function (2) is required because an ATM
connection must be established between adjacent ATM router hops or to the
target ATM address. A multi-layer switch performs only function (3), i.e.
data forwarding.
A route server is used to store next-hop router's layer-3 address, and an
address resolution protocol (ARP) server is used to resolve, i.e.,
translate, layer-3 addresses to ATM addresses. Sometimes these functions
are merged into one server, a so-called "Route/ARP Server". With a
multi-layer LAN switch, the intra-LAN communication is performed just as
in LANE using the local LES and BUS of each ELAN. However, inter-LAN
communication is different. In the following description, Router 151 of
FIG. 2 is assumed to undertake the role of a Route/ARP server.
If host 111-1 wants to talk to host 117-2, then bridge 111-5 acts as a
router, obtains the next-hop-routers IP address from the route server 151,
and obtains the corresponding ATM address from ARP server 151. It then
establishes an ATM connection directly to bridge 117-5 and sends the data
packet.
This method is more efficient than using external router since the external
router hop is eliminated. Further efficiency is obtained by each
multi-layer switch performing fast data forwarding both for layer-2 and 3
packets, while complicated route determination and address resolution
functions are logically removed from the switches. Although the Route
Server decouples the routing from data forwarding, it only can serve a few
logical subnets, and is thus not suited to cover large number of logical
subnets. As the number of subnets governed by a single route server
increases the efficiencies provided with this approach greatly diminish,
since several router hops become practically unavoidable.
Thus, the existing LANE and Route/ARP Server methods work effectively only
for small scale local networks. The LANE solution requires one LES and BUS
per ELAN, and one ELAN per subnet. If an ELAN becomes large, there will be
large numbers of broadcast messages transmitted, which results in a
degradation of network performance. Similarly, a single route/ARP Server
approach is not suitable for large scale networks, as it also creates
performance bottlenecks.
Another problem with the foregoing approaches is the difficulty of handling
frequent moves and changes between ELANs when an ELAN may extend beyond
corporate boundaries and may span several remote sites. For example,
during the life of a project it may be useful for LAN 101 and LAN 103 to
form a single LAN. However, with the above solutions, the assigning of
hosts to a single LAN is not easily manageable, except in the case of
relatively small local networks.
SUMMARY OF THE INVENTION
The forgoing problems with interconnecting ELANs are overcome, in
accordance with the principles of the invention, by employing a so-called
"ELAN contronect network" which is a separate network for interconnecting
the servers of the sub-ELANs, where a sub-ELAN is a part of an ELAN having
its own LES and BUS that may also be configured as a stand-alone ELAN.
Each of the sub-ELANs is connected to the ELAN contronect network via a
point-to-point connection-oriented connection, and the ELAN contronect
network is configured to present itself to each of the servers of the
sub-ELANs as clients thereof. Advantageously, the number of connections
required to interconnect the separate sub-ELAN servers, so as to form an
ELAN containing more than one sub-ELAN, is reduced from an order of
squared (N.sup.2) to an order of linear (KN) with respect to the number of
sub-ELANs that are interconnected. Also advantageously, the number of
broadcast messages transmitted between different sub-ELANs in an ELAN is
reduced from the total number of clients in all of the sub-ELANs that are
interconnected to form the ELAN to the number sub-ELANs in the ELAN minus
one by only transmitting from the ELAN contronect network one broadcast
message to each sub-ELAN, of the ELAN, other than the message originator.
Further advantageously, the sub-ELANs can be coupled to the ELAN
contronect network without changes to the hardware or software of their
servers provided there is a capacity to attach another client.
In a particular embodiment of the invention, the ELAN contronect network
includes an address server and a broadcast/route server interconnected
over a high-speed backbone. Also connected to the high-speed backbone is
at least one LAN hub, which connects to at least one server of at least
one of the ELANs.
The address server contains an address data base for performing address
resolution, i.e., translation, between the at least two addresses of each
ELAN end-point in response to requests for such translations. The
broadcast/route server receives data packets for broadcast to a different
sub-ELAN from which the packets originated and broadcasts the received
data packets to at least one other sub-ELAN. The broadcast/route server
also recognizes that a packet which is a broadcast packet at layer 2 is
actually a request for an address resolution at layer 3. If so, the
broadcast/route server collaborates with the address server to perform the
necessary address resolution and insures that a response is sent only to
the client originating the request. Advantageously, the number of
broadcast messages is reduced to one from a number equal to the number of
clients of the ELAN in which the address resolution request has
originated. Layer-3 routing may also be performed by the broadcast/route
server.
Optionally, the ELAN contronect network also includes a configuration
server and one or more multimedia servers.
BRIEF DESCRIPTION OF THE DRAWING
In the drawing:
FIG. 1 shows two small prior art networks, each representing a different
logical subnet at layer-3;
FIG. 2 shows prior art LAN emulation in which the LANS of FIG. 1 are served
by various servers, i.e., LES and BUS;
FIG. 3 shows an exemplary embodiment of the invention in which an ELAN
contronect network is arranged to interconnect several sub-ELANs in
accordance with the principles of the invention;
FIGS. 4, 5, 6, and 7, when connected together, show an exemplary procedure
for processing packets in the system of FIG. 3, in accordance with the
principles of the invention;
FIG. 8 shows an exemplary process performed by the configuration server of
FIG. 3 for adding new LES, BUS, or route/ARP servers in accordance with
the principles of the invention;
FIG. 9 shows an exemplary process for viewing or modifying an existing
configuration in accordance with the principles of the invention; and
FIG. 10 is a block diagram view of an exemplary embodiment of generic
server 1001, which may be used as the servers shown in FIG. 3.
DETAILED DESCRIPTION
FIG. 3 shows an exemplary embodiment of the invention in which ELAN
contronect network 401 is arranged for interconnecting the servers of
sub-ELANs 207, 219, 227 and 237 in accordance with the principles of the
invention. Each of sub-ELANs 207, 219, 227 and 237 is connected to ELAN
contronect network 401 via a point-to-point connection-oriented connection
through asynchronous transfer mode (ATM) wide area network 131. ELAN
contronect network 401 is configured to present a) address server 247 and
b) broadcast/route server 215 to each of servers 201, 203, 211, 213, 301,
303, 305, and 307 of the sub-ELANs as LECs, and more particularly, as
proxy LECs thereof. Address server 427 and broadcast/route server 215 are
"proxy" in that they represent all other end-station addresses not within
each respective sub-ELAN. Advantageously, the number of connections
required to interconnect the separate ELAN servers is reduced from an
order of squared (N.sup.2) to linear (KN) with respect to the number of
ELANs that are interconnected. Also advantageously, the number of
broadcast messages transmitted between different sub-ELANs in an ELAN is
reduced from the total number of clients in all of the sub-ELANs that are
interconnected to form the ELAN to the number sub-ELANs in the ELAN minus
one by only transmitting from the ELAN contronect network one broadcast
message to each sub-ELAN, of the ELAN, other than the message originator.
Further advantageously, the ELANs can be coupled to the ELAN contronect
network 401 without changes to the hardware or software of their servers
provided there is a capacity to attach another client.
In particular, FIG. 3 shows sub-ELAN 207, sub-ELAN 219, sub-ELAN 227, and
sub-ELAN 237. Sub-ELAN 207 includes prior art network 101 and associated
LAN emulation server (LES) 201, broadcast and unknown server (BUS) 203 and
route/address resolution protocol (ARP) server 151. Sub-ELAN 219 includes
prior art network 103 and its associated servers LES 211, BUS 213, and
route/ARP 311, which substitutes for access to router 151 of FIG. 2.
Sub-ELAN 227 includes bridge and legacy LAN 179, ATM end-stations 131, ATM
switch 175, and associated servers LES 305 and BUS 307. Sub-ELAN 237
includes bridge and legacy LAN 173, ATM end-station 121, ATM switch 193,
and associated servers LES 301 and BUS 303.
ELAN contronect network 401 includes a) address server 427, b)
broadcast/route server 415, c) optional configuration server 419, d)
optional multimedia server farm 421, and e) LAN hubs 431 which includes
LAN hub 431-1 through 431-N, connected via high speed backbone 425.
Address server 427 performs address resolution, i.e. address translation,
between various network end-point layer-3 and layer-2 addresses. As is
well known in the art, each network end-point, i.e., any unit connected to
send and receive data packets, may have more than one address, i.e. an
identifier, by which it is known. Thus, a first end-point may know a
particular address for a second end-point but not the second end-point's
other corresponding address which may be required in order to exchange
data packets with the second end-point. The information necessary to
perform such address translation is stored in an address table. Table 1 is
an exemplary address table. If address server 427 does not contain within
itself the necessary information to perform a required address
translation, i.e., the necessary entries are not present in its address
table, address server 427 is able to engage the necessary processes in
order to obtain and store within itself the necessary information.
Thereafter address server 427 will be able to directly perform the
required address translation.
TABLE 1
______________________________________
ATM address Layer-2 address
Layer-3 address
______________________________________
ATM-111-5 MAC-111-01 IP-111-01
ATM-111-5 MAC-111-02 IP-111-02
. . .
. . .
. . .
ATM-111-5 MAC-111-0N IP-111-0N
ATM-115 MAC-115 EP-115
______________________________________
Broadcast/route server 415 performs several functions relating to
communicating to more than one end-point at a time. In particular
broadcast/route server 415 receives a data packet from a sub-ELAN of a
particular ELAN and sends it to one or more sub-ELANs in the same or a
different ELAN. Broadcast/route server 415 also recognizes that a data
packet which is indicated to be a broadcast packet at layer-2 actually
contains a layer-3 address resolution request. When such data packets are
recognized, broadcast/route server 415 communicates with address server
427 to obtain the requested address. Broadcast/route server 415 then
transmits the translated address directly to the end-point which
originated the data packet. Advantageously, doing so eliminates the need
for additional transmissions of the data packet.
An optional function of broadcast/route server 415 is to act as a router
for packets addressed to it by a router/ARP server and requesting routing
of the packets. Typically such requests are performed at layer 3, and
require a packet to be sent to an ELAN other than the ELAN of the
packet-originating end-point. Advantageously, since broadcast/route server
415 is aware of all the layer-3 addresses of those end points that
subscribe to service by ELAN contronect network 401, packets can be routed
to the ultimate destination in no more than two hops, i.e. via the
route/ARP server of the sub-ELAN from which the packet originated and then
via broadcast/route server 415.
Optional configuration server 419 operates to group one or more sub-ELANs
into an ELAN regardless of the locations of the sub-ELANs. Configuration
server 419 can serve more than one ELAN. For example, configuration server
419 has configured sub-ELAN 207 and sub-ELAN 237 into ELAN 301. Likewise,
configuration server 4 19 has configured sub-ELAN 227 and sub-ELAN 2 19
together into ELAN 371.
Configuration server 419 operates by communicating with address server 427
and broadcast/route server 415 to establish connections between the
servers of the sub-ELANs to be joined into a single ELAN while ensuring
the disjointedness of the distinct ELANs. One method for achieving this
result is to group together at least one set of the addresses
corresponding to servers serving the sub-ELANs of an ELAN in a so called
"configuration table". For example, the addresses employed may be the ATM
addresses. Packets originating from an address within a particular group
of sub-ELANs may only be transmitted to end-points having addresses within
the same group.
By using the same type of arrangement, configuration server 419 also
controls access by the various ELANs and sub-ELANs to services provided by
multimedia server farm 421. This will be further described hereinbelow.
Optional multimedia server farm 421 includes one or more multimedia servers
for providing a variety of multimedia services. The particular multimedia
services available to any particular end-point depends on the services to
which the ELAN to which the end-point belongs, has subscribed. Exemplary
services provided by multimedia server farm 421 include a) multipoint
video teleconferencing, b) multipoint whiteboarding, c) video-on-demand,
and d) delayed playback of retrieved files. In order to obtain such
services, an end-point requests a connection to multimedia server farm 421
as an end-point itself, with the request specifying the particular service
required.
LAN hubs 431 provide conversion from ATM to the protocol of high-speed
backbone 425. For each LES, BUS, and route/ARP server in each of the
sub-ELANs there is a single ATM connection to one of LAN hubs 431. These
are connections 326.
ATM connections 326 traverse a so-called "local ATM network" which is the
portion of an ATM network that is seen by all end-stations of the sub-ELAN
and is used for the LAN emulation therein. ATM connections 326 also
traverse ATM wide-area network (WAN) 131, which provides interconnection
from each local ATM network to LAN hubs 431. The local ATM networks and
ATM wide-area network 131 may all be logical parts of a single ATM
network. The local ATM networks and ATM wide-area network 13 1 carry
properly addressed packets directly between end-points.
FIGS. 4, 5, 6, and 7, when connected together, show an exemplary procedure
for processing packets in the system of FIG. 3, including the performing
of address resolution and forwarding data packets to a specified address,
in accordance with the principles of the invention. The process is entered
in step 501 when an end-station has prepared a packet for transmission.
Next, conditional branch point 503 tests to determine if the prepared
packet is a routable packet i.e., the packet has a layer-3 protocol. If
the test result in step 503 is NO, indicating that the packet is not
routable, control passes to conditional branch point 505, which tests to
determine if the packet is destined to an end-station within the same
ELAN. If the test result in step 505 is NO, control passes to step 507 and
the process is exited.
If the test result in step 503 is YES, indicating that the packet is
routable, control passes to conditional branch point 509, which tests to
determine if the packet is destined to an end-station within the same ELAN
or the packet is a broadcast packet. If the test result in step 509 is YES
or the test result in step 505 is YES, control passes to conditional
branch point 511, which tests to determine if the packet is a control
packet. If the test result in step 511 is YES, control passes to step 513,
in which the end-station transmits the packet to the LES of the sub-ELAN
to which it is connected.
Steps 501-513 are performed in an ATM end-station when it is originating a
packet. An ATM end-station can be a stand-alone ATM end-station, such as
ATM end-station 131, or it may be an ATM to Legacy LAN converter, such as
bridge 111-5 contained in site 111. Such ATM end-stations are known in the
art as LAN emulation clients (LEC).
Control then passes to conditional branch point 515, which tests to
determine if the ATM address of the destination of the packet is found
within the LES. If the test result in step 515 is YES, control passes to
step 517, in which the LES of the sub-ELAN establishes a connection to the
packet-originating LEC if one does not already exist. Next, in step 519,
the LES transmits the requested ATM address to the packet-originating ATM
end-station. The process then exits in step 507. In this instance, steps
517-519 are performed by the LES of end-station's sub-ELAN.
If the test result in step 515 is NO, indicating that the ATM address of
the destination is not contained within the LES of the sub-ELAN of the
packet originating LEC, control passes to step 521, in which the LES
broadcasts an address resolution request to all LECs of the sub-ELAN, and
thus address server 427 of ELAN contronect network 401, which appears as a
LEC to the LES, in accordance with the principles of the invention.
Next, the following process steps are undertaken substantially in parallel
by each of the LECs in the sub-ELAN and a separate set of process steps is
also undertaken in address server 427.
Steps 523 through 525 are performed in each LEC. On receipt of the
broadcast message each LEC tests to determine if it is the destination
LEC, in conditional branch point 523. If the test result in conditional
branch point 523 is NO, indicating that the LEC is not the destination
LEC, control passes to step 525 and the packet including the resolution
request is discarded. Control then passes to step 507 and the process is
exited. If the test result in step 523 is YES, indicating that the LEC is
the destination LEC, control passes to step 524, in which the LEC sends a
packet, including the requested address, to the LES of the sub-ELAN which
originated the address resolution request. Thereafter, control passes back
to step 517, and the process continues as described above in the LES.
In response to receipt of the address resolution request in address server
427, address server 427 tests to determine, in conditional branch point
527, if it itself originated the address resolution request packet. If the
test result in step 527 is YES, control passes to 525, in which address
server 427 discards the packet containing the request. The process then
exits in step 507.
If the test result in step 527 is NO, control passes to conditional branch
point 531, in which address server 427 tests to determine if the requested
destination address is contained within its database. If the test result
in step 531 is YES, control passes back to step 517, and the process
continues as described above, except that steps 517 and 519 are performed
by address server 427 instead of the LES of the sub-ELAN from which the
address resolution request originated.
If the test result in step 531 is NO, control passes to conditional branch
point 533, which tests to determine if the LES serving the destination is
known to address server 427. If the test result is step 533 is YES,
control passes to step 535, in which, in accordance with to the principles
of the invention, address server 427 transmits an address resolution
request only to the LES of the sub-ELAN serving the destination. If the
test result in step 533 is NO, control passes to step 537, in which an
address resolution request is sent to all LESs serving the ELAN,
preferably except the LES of the sub-ELAN originating the request. After
completion of step 535 or step 537, control passes back to step 515, in
which each of the LESs receiving a message from address server 427
continues executing the process at step 515 as described above.
If the test result in step 511 is NO, indicating that the packet is a data
packet, control passes to conditional branch point 539 (FIG. 5), which
tests to determine if the destination address is known to the LEC
originating the data packet. If the test result in step 539 is YES,
control passes to step 541, which tests to determine if the packet is a
unicast packet, i.e., a packet destined to a single end-point. If the test
result in step 541 is YES, control passes to step 545, in which the
originating LEC establishes a connection to the destination address, if
one does not exist already. Control then passes to step 547, in which the
data packet is transmitted over the connection. The process then exits in
step 507.
If the test result in either step 539 or step 541 is NO, indicating that
either the originating LEC does not know the destination address or the
packet is destined for more than one destination address, i.e., a
broadcast or multicast packet, control passes to step 549, in which the
packet is transmitted to the BUS of the sub-ELAN serving the LEC
originating the data packet. Next in step 551, the receiving BUS
broadcasts data packet to all LECs, in the sub-ELAN and, consequently,
accordance with the principles of the invention, to broadcast/route server
415 in ELAN contronect network 401, which is a proxy LEC thereof. As a
result, two distinct parallel paths thereafter result, the first path a)
including steps 553 through 557 and b) being performed in each LEC
receiving the broadcast data packet, and the second path a) including
steps 559 through 579 and b) being performed in broadcast/route server
415.
When control passes to step 553, the LEC receiving the broadcast packet
tests to determine if it is one of the destination LECs. If the test
result in step 553 is NO, control passes to step 557, in which the packet
is discarded. The process then exits in step 507. If the test result in
step 553 is YES, control passes to step 555, in which the receiving LEC
processes the packet, e.g., examines the packet header and transmits the
packet to higher layers. The process then exits in step 507.
When control passes to conditional branch point 559, because
broadcast/route server 415 receives a broadcast packet, broadcast/route
server 415 tests to determine if it had originated the broadcast packet.
If the test result in step 559 is YES, control passes to step 561 and the
data packet is discarded. The process then exits in step 507.
If the test result in step 559 is NO, control passes to conditional branch
point 563, which tests to determine, in accordance with an aspect of the
invention, if the packet is a broadcast packet at layer-2 that originated
in response to a layer-3 address resolution protocol (ARP) request, i.e.,
a request for address translation at layer-3. If the test result in step
563 is YES, control passes to conditional branch point 567, which tests to
determine if the layer-2 address of the destination is contained within
address server 427. This step is performed by broadcast/route server 415
querying address server 427 and receiving a response containing the
desired address therefrom, if it is available. If the test result in step
567 is YES, control passes to step 569, in which broadcast/route server
415 prepares an ARP.sub.-- Response message including the requested
address. Control then passes back to step 517, and the process continues
as described above, except that steps 517 and step 519 are performed by
broadcast/route server 415 and the requested address transmitted is that
of the ARP.sub.-- Response.
If the test result in step 567 is NO, indicating that the destination
layer-2 address is not within address server 427, control passes to
conditional branch point 573, which tests to determine if the BUS serving
the destination LEC is known. If the test result in step 573 is YES, in
accordance with an aspect of the invention, broadcast/route server 415
transmits a layer-3 ARP request only to the BUS serving the destination
LEC. If the test result in step 573 is NO, control passes to step 579, in
which the layer-3 ARP request is transmitted to all the BUSs of the ELAN.
Upon conclusion of the performance of steps 575 or 579, control passes
back to step 551, in which each of the BUSs receiving the request from
broadcast/route server 415 process the request as described above.
If the test result in step 563 is NO, indicating that the packet is a
conventional broadcast packet, control passes to conditional branch point
581 (FIG. 6), which tests to determine if the packet is a broadcast
packet. If the test result in step 581 is YES, indicating that the packet
is a broadcast packet, control passes to step 583, in which
broadcast/route server 415 broadcasts the packet to all the BUSs of the
ELAN from which the packet originated. Control then passes back to step
551 (FIG. 5), and the process continues as described above when each of
the BUSs receives its copy of the broadcast packet.
If the test result in step 581 is NO, indicating that the packet is a
multicast packet, control passes to conditional branch point 585, which
tests to determine if the multicast layer-3 addresses of the multicast
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