Ghost and advanced IGMP functions.

Products

• Ghost Solution Suite

Issue/Introduction

You wish to know how best to configure the IGMP optionsavailable on switches and routers to work with Ghost.
 

Cause

The Ghost Solution Suite uses IGMP to create a specific multicast group for transmission of multicast packets. This means that the IGMP features available on Switches and Routers such as IGMP querying and snooping can be used to optimize the multicast traffic in the Network.

Resolution

IGMP Querying

This is a function that is found on Routers and Layer 3 switches. An IGMP querying router queries any LAN to which it connects at regular intervals, e.g., once a minute. In response to a query, an IGMP host transmits one or more messages reporting its memberships to multicast group addresses. The router dynamically updates memberships to multicast group addresses. In this way the IGMP querying router can maintain a picture of all current multicast traffic on the LAN.

Recommendation: This function allows multicast groups to span several subnets in a network, meaning that Ghost can clone machines on remote subnets using multicast. This option should be enabled on internal routers.

IGMP Snooping

This is a relatively recent feature found on Layer 2 switches that allows the switch to listen in on and react according to the IGMP conversations between hosts and routers. When a IGMP-snooping capable switch hears an IGMP report from a host for a given multicast group, the switch adds the host's port number to the Multicast Address List (aka Group Destination Address) for that group. When the switch hears an IGMP leave group announcement, it removes the host's port from the MAC address table entry. Based on this information the swich will "prune" traffic i.e. not send it to those hosts that are not members of the group for whom it is intended.

Recommendation: This feature allows switches to optimize the bandwidth usage of the connected hosts. This will not impact Ghost traffic If a switch is capable of operating this feature, it should be enabled.