US 5,500,860 AGranted

Router using multiple hop redirect messages to enable bridge like data forwarding

AssigneeDigital Equipment Corporation

InventorsRadia J. Perlman, Alan J. Kirby, Floyd J. Backes, Charles W. Kaufman

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Abstract

An apparatus for forwarding a data packet from a first link to a second link is disclosed. The apparatus is coupled with a plurality of computer networks through ports on the apparatus. The apparatus maintains a spanning tree list indicating which of the apparatus ports are active. The apparatus receives a packet, and determines if the packet was received from a port that is active. If the packet was received from a port that is not active, the packet is discarded. If the packet is not discarded, the data link source address of the packet is stored in a database within the apparatus for the computer network coupled with the port from which the packet was received. The apparatus then decides, responsive to a contents of a data link destination address field in the packet, whether to forward the packet as a bridge or to forward the packet as a router. If the apparatus forwards the packet as a router, the apparatus sends a redirect message to update the data link layer destination address used by the originating station to contain the data link layer address of the destination station where the destination station is on a link remote from the link of the originating station. For the subsequent packets the apparatus then behaves as a bridge by forwarding the subsequent packets based upon parsing of only the Data Link Header. For forwarding of subsequent packets, the apparatus is advantageously fast, in accordance with bridge operation.

Claims6

Dependent claims

A packet forwarding apparatus, physically coupled with a plurality of LANs by a corresponding plurality of ports, comprising:

receiving means for receiving a first packet from a first one of said plurality of ports, said first one of said plurality of ports coupled;
packet discarding means, responsive to said receiving means, for discarding said first packet when said first one of said plurality of ports is not within a spanning tree of the apparatus, said spanning tree of the apparatus containing a list indicating which of said plurality of ports are active;
learning means, responsive to said packet discarding means not discarding said first packet, for storing a data link source address of said first packet in a forwarding database for said first LAN;
testing means, responsive to said learning means, for determining if a data link destination address field value of said first packet is equal to either a data link address of said apparatus, or to a routing multicast address;
router processing means, responsive to said testing means determining that said data link destination address field value of said first packet is equal to either a data link address of said apparatus or to a routing multicast address, for forwarding said first packet based on addressing information in a network layer header and a data link header in said first packet;
and
bridge processing means, responsive to said testing means determining said data link destination address field value of said first packet is not equal to either a data link address of said apparatus or to a routing multicast address, for forwarding said first packet based on addressing information in a data link header in said first packet.

4 more elements

Dependencies are inferred from the claim text.