PXE-Bootproblems after actiating RSTP...

[edv-schuster]

Hello there.

I have a Network-Environment with about 200 PCs and 30 24-port Smartswitches. We use Fog in this Network now for over 6 years without any major problems.

A few days ago, we activated RSTP (not STP) on all our Switches because we get Looping when some employees plugin a wrong cable in the wall…

Some machines now seem to hang during the PXE-Boot of fog. Is there any optimization we could make to handle this problem? (all switches can configure RSTP-Settings like “hello time”, “max.age”, and so on.)

[george1421]

@edv-schuster Actually RSTP is preferred over STP for a few reasons (forwarding right away is very helpful for pxe booting).

Can you provide a clear screen shot of where you are getting stuck? Also having an unmanaged switch (the most basic switch) for testing is also helpful if we need to test more.

[edv-schuster]

we used rstp because it is faster than stp. but it seems, its not fast enough for our switches…


[george1421]

@edv-schuster From your picture it does appear that spanning tree is getting in your way.

As a test you can do 2 things, either one will tell us the same answer.

1. At the screen in the picture you gave, press the s key to get an iPXE shell. Wait 30 seconds and then key in dhcp net0 to see if it picks up an IP address. If not then key in dhcp net1, just in case the second network adapter is being used.
2. Place an unmanged (dumb) switch between the pxe booting computer and the building switch. This unmanaged switch typically will not support spanning tree. See if the computer boots properly into the FOG iPXE menu.

If either of the above tests point to spanning tree, then reinspect this switch to ensure that RSTP is enabled on all switch ports.

RSTP uses optimistic blocking (forward first then decide if there is another switch connected).
STP uses pessimistic blocking (block first then decide if there is another switch connected).

For what ever reason your switch might be blocking first then forwarding (at least based on the picture you provided).

[edv-schuster]

@george1421 thanks for your answer. i will try that.