GMAP
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GMAP

The Group Mobility Advertisement Protocol (GMAP) enables workstation users to move from
port to port among interconnected switches and still retain all learned mobile group and
protocol information. Using GMAP the switch sends a complete list of learned MAC addresses
and associated group/protocol information to all interconnected switches in the network.
Update and retention times are configurable. A switch that receives a GMAP update packet
updates its internal GMAP tables and queries the forwarding database to make any necessary
updates.
At startup time and for three successive update intervals, GMAP sends update packets on all
virtual ports that are active non-leaf ports (that is, ports that are running Spanning Tree).
GMAP packets are sent using the VAP multicast address. After startup and three transmissions,
interval packets will only be sent on virtual ports that are active and are known to have an
OmniS/R running GMAP connected to them.
GMAP will send updates only for MAC addresses that are learned on leaf ports (ports that are
not running Spanning Tree). It does not advertise MAC addresses for groups assigned by
authentication, and it does not advertise group 1 entries or nonmobile group entries. If
conflicting information is received for a MAC address, the last packet received for that address
will take precedence.
When AutoTracker learns a new MAC address on a leaf port it attempts to assign it to a
mobile group. It consults GMAP tables and any appropriate group membership entries are
added to the forwarding database.

GMAP Updating Rules

Upon receiving a packet, GMAP updates its internal tables and queries the forwarding data-
base. When GMAP reviews the forwarding database to update it with new information, it uses
the following rules:
•GMAP will only update information for leaf ports.
•GMAP does not add a new MAC address to a port.
•GMAP will only overwrite group 1 entries. If there is no group 1 entry, it will add a new
entry, provided that it will not create a conflict with existing entries in the forwarding data-
base.
•GMAP will not add an entry for an authenticated group.
•GMAP will not add an entry that is in conflict or potential conflict with a binding rule. A
potential conflict would be a binding rule that requires the IP address be known for the
MAC address. GMAP does not have access to IP information.
•GMAP will not add an entry for a group/protocol pair when there is an existing entry for
that protocol on the requested port.
• When GMAP finds an entry for the desired group already on the switch but not on the
requested port, it will move it to the requested port.
• When GMAP finds an entry with the appropriate group but a protocol value of 0 (indicat-
ing all protocols), it will update the protocol value in that entry to that in its database.