Port Mirroring Considerations - HP AE370A - Brocade 4Gb SAN Switch 4/12 Administrator's Manual

There are two types of transmit filter installation
• If the E_Port is on the same chip, port mirroring installs an egress (transmitted information) filter on the
source port.
• If the E_Port is on a different chip, port mirror installs the filter on the C_Ports of the other chip.
To better explain how the transmit filter works on each of these types, the method used for both types is
described as follows:
• Traffic is received at the E_Ports destined to a source port. The switch routes these frames to the source
port (if the E_Port is on the same chip) or to the C_Ports destined to the source port (if the E_Ports are on
different chips).
• On the same chip, the source port has a mirror to redirect any matching frames to the mirror port. On
different chips, the C_Ports redirect any matching frames to the mirror port.
• The mirror port routes those frames it receives back to the source port (on the same chip) or to the
C_Ports (on a different chip).
When a port goes offline, the mirror connections that are related to this port will be removed. When the
port goes online, if all ports of the connection are online, the mirror connections that are related to this port
will be restored.
For remote ports, connections that are mirroring traffic from a remote domain, when the remote domain
becomes unreachable, the mirror connections related to this domain are removed. When the remote
domain becomes reachable, the mirror connection will only be added if all the ports of the connection are
online too.

Port mirroring considerations

Before creating port mirror connections, consider the following limitations:
• A mirror port can be any port on the same switch as the source identifier port.
• Only one domain can be mirrored per chip; after a domain is defined, only mirror ports on the defined
domain can be used.
For example, in a three-domain fabric containing switches 4100A, 4100B, and 4100C, a mirror
connection that is created between 4100A and 4100B only allows 4100A to add mirror connections for
those ports on 4100B. To mirror traffic between 4100A and 4100C, add a mirror connection on
4100C. The first connection defines the restriction on the domain, which can be either the local domain
or a remote domain.
• A switch that is capable of port mirroring can support a maximum of four mirror connections.
Each FDB defines an offset to search. Each offset can have up to four values that can be defined for a
filter. If any of the four values match, the filter will match.
• Mirror port bandwidth limits mirror connections.
The bandwidth of the mirror port is unidirectional. The host (SID) talks to multiple storage devices (DIDs)
and does not send full line rate to a single target. A mirror port configured at 2GB can only support up
to 2GB of traffic. A normal 2G F_Port is bidirectional and can support up to 4GB of traffic (two to
transmit and two to receive). If the mirror port bandwidth is exceeded, the receiver port is not returned
any credits and the devices in the mirror connection see degraded performance.
• Deleting a port mirroring connection with In Order Deliver (IOD) enabled causes frame drop between
two endpoints.
• Using the firmware download procedure to downgrade to previous Fabric OS releases that do not
support port mirroring requires that you remove all the port mirroring connections. If you downgrade to
a previous versions of Fabric OS, you cannot proceed until the mirroring connections are removed.
304 Troubleshooting