Backbone & Uplink Fast on the Same switch

[Dean Romanelli]

Hi All,

Long story short, I would like to know if it is possible and safe to configure backbonefast and uplinkfast on a common switch?

I would think that since backbonefast detects indirect link failures and uplinkfast detects direct (i.e. local failures), that it would be recommended to configure backbonefast on ALL switches, including access distro switches, and uplinkfast as well, on switches with blocked ports.

Is this correct?

Also, it is my understanding that this stuff is all enabled by defulat in RSTP.  Why not just enable that and be done with it?

[blau grana · Accepted solution]

Hello Dean,

Yes, you are right, uplinkfast and backbonefast is by default implemented in RSTP so if you can, you should prefer this version over CST (Common STP).

backbonefast - is used to detect indirect link failure via RLQ request/response and should be configured on all switches in topology (to support this feature) except access switches. Why? If switch (backbonefast) do not receive hello (BPDU) or receive inferior BPDU, switch starts to think that maybe path to root failed, so it sends RLQ request via port on which hello was not received (root port). If RLQ response is received on root port, path to root is OK, if not, new path must be considered. Important point is that RLQ requests are sent toward root bridge. If network is properly designed, root bridge is in network backbone, not access layer. So access layers switches do not have to understand RLQ because they should never recaive any.

uplinkfast - used if multiple uplink links are availaible. enable to immediately replace failes uplink with new one, no need to wait for max-age expiration. used only in access layer switches, after enabling, these changes are made:

- increase root priority to 49152

- set port cost to 3000

- track possible root ports (ports on which root hellos are received)

Best Regards

Please rate all helpful posts and close solved questions

[Dean Romanelli]

Very good.

Thank you both.

[Joseph W. Doherty]

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Posting

Yes, backbone and uplink fast are in RSTP, so if the switch supports them, it makes sense to enable it.  (NB: in fact, if they are enable when you enable RSTP, RSTP will indicate they been disabled [as separate features].)

The reason for backbone and uplink fast, they were Cisco proprietary features before there was RSTP.  They're such a good idea, they were incorporated into RSTP standard.