Cisco Nexus 5000 and Fex 2000

[Roberto Pancrazio Loiudice]

Hello all,
currently I have a network scenario with a couple a Cisco Nexus 5596UP and several Cisco Nexus 2000 (2232PP, 2248TP ecc.) connected to the parent switch (N5K) in single-homed FEX topology. Is it possible to convert the N2K from single-homed to dual-homed FEX topology without, or minimal, interruption of traffic?

Thanks a lot in advance. Roberto Loiudice

[Mark Malone]

Hi all you have to do is replicate the config on the 2nd 5k,the 2k is already up so it wont have any effect as its received its image already so nothing should go down its just another uplink in the port-channel

[Roberto Pancrazio Loiudice]

Are you sure? I think I have to do a enhanced vpc. In the time where the configuration are not replicated Could I have problems?

[Mark Malone]

you do need an enhanced vpc you can set one side thats already connected adding vpc to the po should not have any effect on it , can you post what config you have for the uplink currently

your config should look like this below and then all you do is replicate it on the other 5k and connect it , the only time a FEX should cause issues is when it first originally gets connected and it pulls its image etc from the 5k, the fact the 5ks are already in a vpc domain together the 2k should not go through any new updates/procedures as its already part of 1 5k

interface port-channel101
  description FEX101
  switchport mode fex-fabric
  fex associate 101
  logging event port link-status
  vpc 101

interface Ethernet3/1
  description FEX101
  switchport mode fex-fabric
  fex associate 101
  logging event port link-status
  channel-group 101

fex 101
  pinning max-links 1
  description "FEX0101"

[Roberto Pancrazio Loiudice]

Thank Mark.

Yes, I have this configuration but without "vpc xxx" under port-channel interface. I'm not sure about what could happen at the moment when the other 5k, in vpc domain, will see the 2k which for it is a new device: it will have no configuration to the new fex interfaces! I think that the consistent parameter of the vpc will not match between both 5ks until I will configure the new interfaces, and I think that this could bring down the interfaces. Do you think that this not will happen?

[Mark Malone]

  i would always have a maintenance window to cover yourself , it may drop the interfaces for a second while you paste the config from first 5k over to the 2nd

you could turn off the consistency check either while you do it but i would just let whoiever maintains the end devices there may be a hit for minute or 2

switch(config-vpc-domain)# peer-config-check-bypass

Disables the default vPC behavior when a peer link is down. This allows newly configured vPCs (and existing vPCs that may get flapped) to be brought up even when a peer link is down and the vPC switch role has been determined to be primary.

[Roberto Pancrazio Loiudice]

Thank Mark,

in order to migrate fex ST to AA mode, is necessary to have maintenance window because is needed reconfigure HIF's configuration. For example, if you have virtual-port-channel with two HIF beetween two ST fex, when you migrate the two fex in AA-mode, you will have to change vPC to a normal PC (vPC is intrinsic and automatically created).

Roberto Loiudice

[Mark Malone]

personally I would never work on Data centre device without maintenance window for the device or a proper change control in place but that's a personal thing from experience its always best to have it, I have added lots of Fexs in and made changes to them and the parent switches without issue so your probably fine to go ahead I just worry that I might fat finger something make a mistake or even hit some irregular bug that causes something you weren't prepared for and thats where the MW comes in handy just covers yourself