Subject: [rbridge] TRILL nickname

From: Vishwas Manral <[email-masked]>
Date: Thu, 30 Sep 2010 16:37:48 -0700

Hi,

I noticed some conflicting concepts for nicknames.

   o  Once an RBridge has successfully acquired a nickname it SHOULD
      attempt to reuse it in the case of a reboot.

and

  o To minimize the probability of nickname collisions, an RBridge
      selects a nickname randomly from the apparently available
      nicknames, based on its copy of the link state. This random
      selection can be by the RBridge hashing some of its parameters,
      e.g., SystemID, time and date, and other entropy sources, such as
      those given in [RFC4086], each time or by the RBridge using such
      hashing to create a seed and making any selections based on
      pseudo-random numbers generated from that seed [RFC4086].

Time seed and random number will make the nickname not unique. In my
view we should try to generate a name based on parameters like
system-id, router-id or other such parameters which will give a random
value rather than time.

Otherwise we have to uselessly store the name in the NVRAM.

Thanks,
Vishwas
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---

From: Donald Eastlake <[email-masked]>
Date: Thu, 30 Sep 2010 20:59:49 -0400

Hi Vishwas,

>      attempt to reuse it in the case of a reboot.

This is to encourage nickname stability. Acquired means that it is
using the nickname and, based on examining the link state database, it
does not see that nickname in use elsewhere in the campus.

> Time seed and random number will make the nickname not unique.

I don't understand your statement. This is only exercised when an
RBridge needs to select a nickname, which is typically when it sees
its nickname held by a higher priority user in the campus or possibly
at start-up. If it is selecting a nickname, it uses the pseudo-random
number it generates to select from the "apparently available
nicknames", that is, from the nicknames that, based on the link state
database, do not appear to be in use. How can using a pseudo-random
number to select among the names that appear to not be in use always
result in a name that appears to be in use?

> In my

What it says is "e.g., SystemID, time and date, and other entropy
sources".  "e.g." means "for example".  Since it throws in "other
entropy sources" you can use whatever you want. It does list
system-id, which you recommend. Have you looked at the referenced RFC
4086?

> Otherwise we have to uselessly store the name in the NVRAM.

The advice to store the nickname (or nicknames) you are holding for
use after re-boot has to do with promoting nickname stability. I don't
understand how you think it is coupled to the method some RBridge uses
for pseudo-random number generation as part of selecting a new
nickname when they need to select a new nickname.

> Vishwas

Thanks,
Donald