maple table: L2_UC
Details
- Name
- L2_UC
- Feature
- TABLE_ACCESS
- Type
- 0
- Entries
- 8192
- Data width
- 96
- Control register
- TBL_ACCESS_L2_CTRL
- Data register
- TBL_ACCESS_L2_DATA
Description
An L2 unicast entry.
L2 unicast entries are distinguished from multicast entries by the multicast bit in the MAC address being 0. This bit is the LSB of the first byte of the MAC address, meaning MC MAC addresses will start with ‘x0-xx-…’, ‘x2-xx-..’, etc.
For unicast entries, forwarding is based on the MAC address and the Relay-VLAN ID (RVID) (*). Together they are hashed to create the key into the this table. The table also has a VLAN entry which defines the VLAN that is assigned to the packet matching this table entry during forwarding operation. Note that RVID and VID can be different. Entries in VLAN 100 will be assigned VID 100 and RVID 100 by hardware learning. However, entries learned from packets without a VLAN tag have VID 0, while RVID is RVID 1 and will follow forwarding rules set up for VLAN 1.
For matching against the RVID, both the inner and outer VID of a packet can be used, this can be defined per VLAN. In OpenWRT we are forwarding based on the inner VLAN-ID. The inner VLAN-ID is the VLAN derived from the VLAN-Tag of the packet during ingress translation, the outer VID is the 802.1q tag. During forwarding the inner VID is mangled by the L2 forwarding decision and then on egress can be again translated into a different 802.1q tag.
(*) It is also possible to use a dedicated Forwarding ID (FID) instead of the RVID, which is based on the MSTI. This is configurable per vlan. In OpenWRT we use the RVID exclusively.
Fields
| Name | LSB | Bits | Description |
|---|---|---|---|
| IP_MC | 86 | 1 |
1: this is an IP multicast table entry. Must be 0 for L2_UC entries. |
| IP6_MC | 85 | 1 |
1: this is an IPv6 multicast table entry. Must be 0 for L2_UC entries. |
| STATIC | 83 | 1 |
A static entry that does not age. |
| AGE | 81 | 2 |
|
| SLP | 76 | 5 |
The source port this MAC address was learned from (Source Learning Port) |
| VID | 64 | 12 |
VLAN-ID assigned to packets matching this entry. |
| SA_BLK | 63 | 1 |
Block this as source address. |
| DA_BLK | 62 | 1 |
Block this as destination address. |
| SUSPEND | 61 | 1 |
|
| NEXT_HOP | 60 | 1 |
This entry is actually a next hop entry, see L2_NEXT_HOP |
| MAC | 12 | 48 |
The MAC that has been learned for forwarding. |
| FID_RVID | 0 | 12 |
The Forwarding ID or Relay VLAN-ID, both used as part of the hash key to find this entry together with the MAC. |