Hi John, On Thu, Sep 23, 2010 at 2:13 PM, John Neiberger <jneiber...@gmail.com> wrote: > The engineer said that on all Cat 4K > devices, we should be using 0x2 as the configuration register. I told > her that I normally used 0x2102, but she said not to use that on these > switches, that 0x2 was the recommended setting on all 4K platforms. > > Does that sound right to you all? It seemed overly general to me, but > apparently this boot issue is a known problem and using a setting of > 0x2 is a reliable workaround. > > Any thoughts?
Breaking it down.. The configuration register contains 16 bits. The 4 least significant bits (bits 0-3) make up the boot field. If set your config-register to 0x2, you're flipping bit 1 on and leaving all other bits set to 0. All values from 0x2 to 0xF (inclusive) in the boot field result in the same behaviour. (best viewed with a fixed-width font): boot ------------|---- 000000000000|0000 | 0000 = 0x0 (does not autoboot) 0001 = 0x1 (boot first image in flash) 0010 = 0x2 (boot based on 'boot system ..' commands) 0011 = 0x3 | 0100 = 0x4 | 0101 = 0x5 | 0110 = 0x6 | 0111 = 0x7 | 1000 = 0x8 | 1001 = 0x9 | 1010 = 0xA | 1011 = 0xB | 1100 = 0xC | 1101 = 0xD | 1110 = 0xE | 1111 = 0xF V OK, so what does a config-register of 0x2102 do? 0x2102 (hex) = 0010000100000010 (binary). The 'on' bits (i.e. set to '1') are bits 13, 8, 1 bit 1 = part of the boot field (as explained above) bit 8 = unused on cat4k bit 13 = determines how the router responds to a netboot failure (off by default) So my take on this is that you're not likely to see much of a functional difference between 0x2102 and 0x2 -- the important bit (literally!) is bit 1, which is set/on with 0x2 and 0x2102. Maybe the cat4k has some special .. features .. that make flipping bits 8 and 13 on a problem. Did the engineer explain why? Some platforms behave differently when bit 1 is flipped. The cat4k doesn't fall back to booting from flash, whereas other platforms do. I can see a problem if you had bad 'boot system' statements but aside from that, based on the docs, I don't see an issue. See: http://www.cisco.com/en/US/partner/docs/switches/lan/catalyst4500/12.2/52sg/configuration/guide/supcfg.html#wp1021899 cheers, Dale _______________________________________________ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/