Unable to set STP Path Cost to less than 16

[david.sovereen@mercury.net]

Hello,

I am on 1.3.8 and seem unable to set the path cost to anything under 16. My other switches have a path cost of 10, and so to to have STP use the shortest path based on number of switch hops, I want to set the Netonix to use 10 as well, but see unable.

I read through the release notes for 1.3.9 and 1.4.0rcX and didn't see anything mention of a change to this. Rather than configure all of my other switches to use a path cost of 16, I'd rather get my Netonix switches to do 10 (fewer of them to reconfigure, and dividing by 10 makes it easy to see how many switch hops you are from root).

Can this be fixed?
Thanks,

Dave

[mike99]

Some swich use multiple of 16 (0 to 240), other 0 to 15. 10 is same as 160 (10 multiple by 16).

[david.sovereen@mercury.net]

Not as we are seeing it. With my Mikrotik bridges/switches, for example, each Mikrotik switch in the path from the root bridge adds 10 to the path cost.

Root <> Mikrotik <> Mikrotik <> Mikrotik
creates a path cost of
0 <> 10 <> 20 <> 30

But with a Netonix in there, I get this:

Root <> Mikrotik <> Netonix <> Mikrotik
creates a path cost of
0 <> 10 <> 26 <> 36

I need the Netonix to allow a value of 10, and I see no reason for it to force a minimum of 16. On Cisco, I can set a cost of 1-65535 on any port using the "set spantree portcost <interface> <cost>" configuration command.

I think this is a bug that it won't take a value less than 16.

Dave

[sirhc]

Well I am back tracking here, Eric informs me 16 is the lowest value our switch core will accept. - SORRY

[mike99]

From a HP procurve:
HP-2530-24G(config)# spanning-tree 24 priority
<0-15>

So only 16 value in port priority for HP procurve.

I don't have access to cisco right now but I'm pretty sure it would be the same. 0-65535 is for root switch priority, not port priority, and it by step of 4096 for root switch priority value.

Mikrotik don't seem to follow industrie standard for STP but port priority is from 0~255

priority (integer: 0..255; Default: 128)
Source:http://wiki.mikrotik.com/wiki/Manual:Interface/Bridge

[mike99]

For Cisco:

port-priority -

Port priority; valid values are from 2 to 255. The default is 128.
Note: When configuring port priority using an interface template, the range is from 0 to 240 in increments of 16.
Source: http://www.cisco.com/c/en/us/td/docs/io ... 2333544803

So, for maximum compatibility, when having the choise between 0-255, use increments of 16 for compatibility with all device, most use this standard. If range is from 0-15, multiply it by 16 to know the corresponding value.

[david.sovereen@mercury.net]

Your replies have jumped this conversation to this being a discussion of Port PRIORITY, but my issues is one of Port COST.

For Port PRIORITY, yes, values of 0 - 240 in increments of 16 are typical.

For Port PRIORITY, the Netonix, Cisco, and Mikrotik all default to 128. Note that Mikrotik switches show the value in hex (80), which equates to 128 in decimal.

For Port COST, however, values starting at 1 are valid on the Ciscos and Mikrotiks. Only the Netonix has this 16 minimum limit. From

http://www.cisco.com/c/en/us/td/docs/sw ... #wp1020470

---
spanning-tree cost cost

Configure the cost for an interface.

If a loop occurs, spanning tree uses the path cost when selecting an interface to place into the forwarding state. A lower path cost represents higher-speed transmission.

For cost, the range is 1 to 200000000; the default value is derived from the media speed of the interface.
---

It seems very strange that Vitesse would have this odd limitation. Can you confirm that this truly is a limitation in the Vitesse switch, and that Port COST hasn't simply been confused with Port PRIORITY? It should also be noted that the Netonix web interface will allow values in increments of 1 starting at 16 (i.e. 17, 18, 19, etc are all valid). This really appears to be just a bug in the error-checking of the Netonix web interface--that it is wanting a minimum of 16 when it really should just need a minimum of 1.

Thanks,

Dave

[david.sovereen@mercury.net]

I just verified using SSH that the Vitesse will definitely take path costs as low as 1, and accepts the same range as the Cisco:


sw-1.twrvwi-4.mercury.net(port 1)# stp


path_cost The STP path cost for this port. Clear this for Auto.

priority The port priority when selecting an interface to put into the forwarding state


sw-1.twrvwi-4.mercury.net(port 1)# stp path_cost


<1-200000000> Path cost


sw-1.twrvwi-4.mercury.net(port 1)# stp path_cost 1


Looks like a bug in the error-checking in the web interface.

Dave

[Eric Stern]

It will be fixed in the next release.

[mike99]

Your replies have jumped this conversation to this being a discussion of Port PRIORITY, but my issues is one of Port COST.

Oups, sorry about this. Give more attention to the 16 value than the option name. My bad.