LevelOne GSW-2600TXM Class-of-Service CoS Support, Bootp / Dhcp Relay, Dvmrp Routing Protocol

4.4.4.DVMRP Routing Protocol

The Distance-Vector Multicast Routing Protocol (DVMRP) behaves somewhat similarly to RIP. A router supporting DVMRP periodically floods its attached networks to pass information about supported multicast services along to new routers and hosts. Routers that receive a DVMRP packet send a copy out to all paths (except the path back to the origin). These routers then send a prune message back to the source to stop a data stream if the router is attached to a LAN which does not want to receive traffic from a particular multicast group. However, if a host attached to this routing switch issues an IGMP message indicating that it wants to subscribe to the concerned multicast service, this switch will use DVMRP to build up a source-rooted multicast delivery tree that allows it to prevent looping and determine the shortest path to the source of this multicast traffic.

When this switch receives the multicast message, it checks its unicast routing table to locate the port that provides the shortest path back to the source. If that path passes through the same port on which the multicast message was received, then this switch records path information for the concerned multicast group in its routing table and forwards the multicast message on to adjacent routers, except for the port through which the message arrived. This process eliminates any potential loops from the tree and ensures that the shortest path (in terms of hop count) is always used.

4.5.Class-of-Service (CoS) Support

The switch provides two transmit queues on each port, with a weighted fair queuing scheme. This function can be used to provide independent priorities for various types of data, such as real-time video or voice, and best-effort data.

Priority assignment to a packet in the switch can be accomplished in any of the following ways:

•Priority can be explicitly assigned by endstations which have applications that require a higher priority than best-effort. This switch utilizes the IEEE 802.1p and 802.1Q tag structure to decide priority assignments for the received packets.

•A port may be manually configured as high priority. In this case, when any other port receives traffic from a high-priority port, that traffic is automatically placed in the high-priority output queue.

4.6.BOOTP / DHCP Relay

Dynamic Host Configuration Protocol (DHCP), described in RFC 1541, is an extension of the Bootstrap Protocol (BOOTP). DHCP allows hosts on a TCP / IP network to dynamically obtain basic configuration information. When a DHCP client starts, it

188