FEX

  1. Fabric Extender (FEX)
  2. VN-tag

Fabric Extender (FEX)

  • EoR + ToR
  • Nexus 2k
  • no local switching
  • cannot be connected to switch (hardcoded BPDU guard), only end host on L2
  • VN-tag between FEX and parent:
    1. IEEE 802.1BR
    2. VIF: virtual interface
  • edge ports
  • static pinning: if uplink fails, all downlinks mapped to it → down
(config)# install feature-set fex
(config)# feature-set fex

; ID – unique across VDCs
(config)# fex <ID>
(config-fex)# type <TYPE>

; 1 default ≡ all hosts via single link, static pinning
(config-fex)# pinning max-links <N>

; enable FCoE
(config-fex)# fcoe
(config)# interface port-channel <N>
(config-if)# switchport mode fex-fabric

; dynamic pinning, max-links = 1 ≡ all traffic via port-channel
(config-if)# fex-associate <ID>
# show fex
# show interface port-channel <N> fex-intf

VN-tag

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            EtherType          |d|p|       Destination VIF     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L|R|Ver|       Source VIF      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

d: direction

  • 0 ≡ host-to-network
  • 1 ≡ network-to-host

p: pointer, 1 ≡ mcast frame, egress replication
L: looped, 1 ≡ frame is sent back to source N2k
R: reserved
Destination VIF: 0 ≡ from N2k, undefined
Source VIF:

  • set by N2k
  • set by master (copied), if received from N2k