Re: [Idr] [spring] New draft for data center gateways

[Robert Raszuk <[e-mail]>]

Hi John,

*[JD]  We were assuming that a) GW/backbone links would be advertised in
> BGP LS (optionally w/ EPE) and b) a GW that is disconnected from the
> backbone does not advertise an auto-discovery route.  This will be made
> explicit in the next revision.  *
>

​Ad a) - EPE works fine with next hop self on the ASBRs of the bacbone. So
if your proposal requires external links to be passive in the backbone IGP
then the draft needs to state it well. Besides it may not be sufficient if
more then one backbone instance is used to interconnect DCs.

Ad b) - The current set of procedures described in section 2 for
constructing auto discovery routes is not sufficient. GW may be
interconnected to more then one backbone each serving different set of
prefixes within each DC (you call it X). So much more would need to go into
the auto-discovery to make this work in practice. And even if you would go
that way it will be slow to re-advertise all prefixes with different tunnel
attribute content.

*[JD]   Are you simply repeating the opinion you expressed when the
> tunnel-encaps draft first came out, or do you have a scalability concern
> that hasn't already been discussed?*
>
>
​I am expressing the observation that tunnel-encaps may work well to pass
static information or information which may change by configiration.

Here you are using it to pass remote reachability info embedded into it. I
find it far from optimal which as combined with possible DC prefix scale is
likely to cause more issues then benefits.

That's why I suggest use of indirection layer to solve this overall
problem. As mentioned one could be LISP or any other SD-WAN solutions.

Thx,
R.