KS8995MA Evaluation Board User’s Guide
Micrel Inc. Confidential
Page 20
11/3/2006
Interpretation of results: The RxLoPriorityByte counter is incremented for all ports because
the priority feature is not turned on. All packets are considered low priority. Port 1 shows
100000 CRC error packets and 100000 64 byte packets received. Note that the Rx64Octets
counter increments even when the packets have CRC errors. Port 2’s counter show 100000
fragments received, which is consistent with the packets sent from the smartbits tester. A
fragment is defined as a packet that is less than the minimum packet size and has a CRC
error. The undersized packet is defined as a packet that is less than the minimum packet size,
but has a valid CRC. Port 3 shows 100000 undersized packets. Port 4’s counter shows
100000 oversize packets. An oversized packet is defined as a packet larger than the
maximum packet size.
6.2 Tag Based VLAN
The KS8995MA supports 16 different tag based VLANs. There are 12 bits in the IEEE
802.1Q VLAN ID field, allowing for 4096 different VLAN ID’s. The KS8995MA supports
16 active VLANs. Any one of the 4096 available VLAN ID’s can be specifed as one of 16
active VLANs in the KS8995MA. If a non-tagged packet or a null VID packet is received,
the KS8995MA will use the ingress port’s programmable default VID for look up.
Figure 6 Tagged Ethernet Packet
The following scenario demonstrates how to use the tagged based VLAN feature in the
KS8995MA. The objective is to create two separate VLANs and show that they are isolated
from one another. VLAN 1 will have in its membership ports 1, 2, 3 and 5. VLAN 2 will
have in its membership ports 4 and 5. If an incoming packet is not tagged, the KS8995MA
has a feature that will use the ingress port’s default VID for port forwarding. The
KS8995MA also has an optional feature to discard packets whose VID port membership in
the VLAN table does not include the ingress port.
