LSA ID Collision help

[Ondrej Zajicek]

On Thu, Mar 17, 2016 at 06:14:24PM -0400, Jigar Mehta wrote:
> Hi ,
> 
> I cannot recreate this scenario at will but had some success when
> restarting protocols or rebooting the linux box or feeding 1000+ routes (to
> BGP and redistribute to OSPF in router) to the setup mentioned above.
> My IP address space was not overlapping either, so the LSA ID generated
> would have been unique.
> 
> Also, I noticed that if I insert overlapping addresses in my protocol and
> redistribute to OSPF , I see LSA ID collisions (bug ?)
> Eg:
> 2016-03-17 16:29:21 <ERR> ospf_0: LSA ID collision for 10.0.192.127/32
> 2016-03-17 16:30:31 <ERR> ospf_0: LSA ID collision for 10.0.192.0/25

Hi

I don't know about the first case, but the second case (with overlaps) is
expected. For each prefix, the number of possible subprefixes is about
about two times larger than the number or possible LSA IDs. BIRD uses
static assignment of LSA IDs <-> prefixes, so there are collisions even
if just some subprefixes are originated.

There is a simple rule to avoid LSA ID collisions - when exporting a
prefix, do not export /32 representing the first and the last IP address
in that prefix. Other overlapping prefixes should be fine.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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