Re: Cisco 2970 and VIA Rhine PXE bootstrap problems

Peter Cordes wrote:
> [...]
>  I haven't had autoneg problem within my clusters (My D-link gigabit switch
> has served well :), but the University network uses Cisco switches,
> sometimes with autonegotiation disabled.  The only problems I've ever had
> with autoneg, ironically, are with Cisco switches where some genius turned off
> autonegotiation, presumably in the interests of avoiding problems!  I
> have to have   mii-tool -F 100baseTx-FD  in my network config stuff on my
> desktop and on the cluster master node (for its external connection).

Hello, Peter.

I didn't realise the Cisco STP discovery and port setup took so long...

The 3COM 3C2000 NIC's we use are evidently more tolerant of these delays 
than the VIA Rhine II's. The good news is that our cluster nodes boot up 
a lot faster now! I'm guilty of assuming that the 'best' option was 
auto-negotiation, which is the default. Clearly that is not the case. 
I've now set *all* ports on the 'system' network (i.e. PXE boot network) 
to be:

     portfast: enabled when static access

This, I think, means that if a port is connected to another switch the 
portfast feature will be automatically disabled. Please let me know if 
you think there is a 'better' way of setting up Cisco 2970 switches.

>  (On my desktop, since I want to run a DHCP client (dhcp3-client), I had to
> add a script /etc/dhcp3/dhclient-exit-hooks.d/local-force-100tx-fd:
> [...]
>  This has actually been working for me for the last couple months, and I
> never have to manually do anything after booting up my desktop at work to
> get networking working.  This is in contrast to the few years when I've
> mostly just left my computer on, partly for bittorrent (KNOPPIX and things
> like that, nothing too inappropriate for work!), partly because broken
> networking was a pain.
 >
>  If Cisco had a setting that would make the switch port use the autoneg
> protocol, but only offer a single speed/duplex that you wanted to force,
> that would totally take care of the problem; people with well-behaved
> network cards wouldn't be forced to manually configure anything on their
> end.  (I read plenty of harsh words directed at Cisco while googling about
> autonegotiation...  I haven't personally used Cisco gear, just been on the
> receiving end of its apparent braindeath.)  I think turning off autoneg
> precluded the use of flow control, since it's autonegotiated and mii-tool
> doesn't have a way to force it on that I know of.

I think the 'portfast' setting I used above will do that, won't it?

> mycluster:~# mii-tool 
> eth0: negotiated 100baseTx-FD flow-control, link ok
> eth1: 100 Mbit, full duplex, link ok
> 
>  The moral of this story is:  autonegotiation is good.  All modern NICs do
> it correctly and compatibly (right?).  Leave it on and you won't have to
> manually do anything to every machine whose default isn't 100baseTx-FD.

I did have a problem like this some time ago when one or two NIC's 
needed to be reset and restarted using "mii" to bring them back to life, 
but this was when we were using passive hubs instead of switches :-(

	Tony.
-- 
Dr. A.J.Travis,                     |  mailto:[email protected]
Rowett Research Institute,          |    http://www.rri.sari.ac.uk/~ajt
Greenburn Road, Bucksburn,          |   phone:+44 (0)1224 712751
Aberdeen AB21 9SB, Scotland, UK.    |     fax:+44 (0)1224 716687


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