[c-nsp] general question on VRFs and FIBs...

[Robert Raszuk]

Hi Gert,

 > "address first, VRF second".

Well no one sane would do that ;) I believe what Derick was asking was 
why not have "incoming_interface/table_id -> prefix" lookup.

And while in software each VRF has separate RIB and FIB data structures 
for reasons already discussed on L3VPN IETF mailing list in actual 
hardware on a given line card however this may no longer be the case.

Also side note that most vendors still did not implement per 
interface/per vrf MPLS labels (even in control plane) so all labels are 
looked up in a global table with just additional essentially control 
plane driven twicks to protect from malicious attacks in the case of 
CSC/Inter-AS.

Cheers,
R.

> Hi,
>
> On Mon, Sep 26, 2011 at 01:18:05PM -0700, Derick Winkworth wrote:
>> I'm trying to find an archived discussion or presentation discussing
>> why exactly the industry generally settled on having a separate
>> FIB table for each VRF vs having one FIB table with a column that
>> identifies the VRF instance?  I'm not finding it, but I'm guessing
>> its because of performance issues?
>
> Lookup would fail for overlapping address space if you lookup
> "address first, VRF second".
>
> How do you find the right entry if you have
>
>    10.0.0.0/8 vrf red
>    10.0.0.0/16 vrf green
>    10.0.1.0/24 vrf blue
>
> and try to look up 10.0.0.1 in vrf red?  You'll find the /24 entry, which
> is tagged "vrf blue".
>
> Alternatively, you'd need to explode the /8 entry for vrf red if *another*
> VRF adds a more specific for that /8.
>
> gert
>
>
>
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