Information About VN-Segment
The VN-Segment feature defines a new way to "tag" packets on the wire replacing the traditional 802.1Q VLAN tag. This feature uses a 24-bit tag also referred to as a Virtual Network Identifier (VNI). CE links (access and trunk) carry traditional VLAN tagged/untagged frames. These are the VN-Segment Edge ports.
FabricPath links (switchport mode fabricpath ) carry VN-Segment tagged frames for VLANs that have VNIs defined. These are the VN-Segment core ports.
The previous figure shows a typical Cisco FabricPath network. Switches S1 and S2 are the spine switches. Switches S3 and S4 are the leaf switches and are connected to the spines over FabricPath interfaces. The VN-Segment feature is enabled on all leaf switches.
Server A is connected to leaf switch S3 and server B is connected to leaf switch S4 through normal Layer 2 trunk/access ports. These interfaces are also referred to as the "VNSeg Edge" ports. The servers send and receive traditional .1Q tagged or untagged frames. No new configurations are needed on the servers. The spines forward the VN-Segment tagged frames to the intended leafs.
Assume that servers A and B need to be in the same Layer 2 flood domain.
On the leaf switches, VLAN 333 is mapped to an available VN-Segment ID 16535. This VN-Segment ID identifies the VLAN 333 on the FabricPath network.
Here is a typical packet flow:
A data packet from server A to server B tagged with VLAN 333 is received on the VNSEG port of S3.
S3 does the packet lookup and sends the packet on the FabricPath port towards the spine. The switch S3 uses the VN-Segment ID corresponding to the VLAN.
S1 and S2 performs FabricPath forwarding towards the intended leafs.
S4 receives the VN-Segment ID tagged packet and performs packet lookups. Once the packet destination port is identified as a VNSEG edge port, S4 uses the VLAN ID corresponding to the VN-Segment ID in the packet and sends the packet.
If the VN-Segment ID to VLAN mapping does not exist, the packet is dropped.
Server B receives the .1Q data packet from Server A.
The same process is followed in the data packets from server B to server A.