Subject: [VRRP] May, should, must confusing section 7.1 vrrp

From: "Stephen Nadas" <[email-masked]>
Date: Mon, 6 Apr 2009 17:11:31 -0500

Hi Don, 

I'm trying, once again, to clean this up.   Been busy elsewhere... 

Mark H. pointed out: 

> Section 7.1:
> 
> - MAY verify that "Count IPvX Addrs" and the list of IPvX Address
>       matches the IPvX Address(es) configured for the VRID
> 
>    If the above check fails, the receiver SHOULD log the event and MAY
>    indicate via network management that a misconfiguration 
> was detected.
>    If the packet was not generated by the address owner (Priority does
>    not equal 255 (decimal)), the receiver MUST drop the packet,
>    otherwise continue processing.
> 
> This combination of MAY, SHOULD and MUST is confusing.  Also 
> it's not clear if the second "If" is conditional on the first 
> "If".  It seems like you may have a mandatory action that you 
> can't do unless you do an optional action.
> 

So I agree it's confusing.  The text (from rfc, and -v6 and from
combined) all say the same.  In particular the immediately prior text
isn't much better: 

      - MUST verify that the VRID is configured on the receiving
        interface and the local router is not the IPv6 Address owner
        (Priority equals 255 (decimal)).

   If any one of the above checks fails, the receiver MUST discard the
   packet, SHOULD log the event and SHOULD indicate via network
   management that an error occurred.

      - MAY verify that the IPv6 Address matches the IPv6_Address
(As above...)

So here's my questions: 

1) the check that the _local router_ isn't the IPvX address owner need
not say anything about _Priority 255_.  Right?  That is confusing and
afaict irelevant (If I get an adv for an address I own I must drop  &
shld log)  

2) I am confused about the check that the packet came from the address
owner.  (Why can't I can get an adv from a master who is not the address
owner, eg a dfferent backup for a down master address owner.)  

Is this latter a stand alone check that is really needed? (or maybe some
text that has just been carried along?)  it doesn't seem to have
anything to do with the preceeding MAY (which seems to be essence of
Mark's comment.) 

Thanks,
Steve