[rrg] [lisp] Economic issues of long-path / stretched routing

[John Zwiebel]

On Jan 25, 2009, at 1:53 PM, Benson Schliesser wrote:

> My single-homed xTR (savvis) has one ALT peer right now (asp) and  
> he announces an aggregate net that covers my EID prefix. That's  
> great from a routing scale perspective. However if I were to  
> multihome to another net (dmm, for example) wouldn't I have to  
> announce my EID into the ALT via that path if I wanted to continue  
> serving that EID during an outage of my primary (asp) connectivity?
>

Yes you should, but that doesn't add another route to the ALT routing  
table.
> At the very least it has to be announced such that my primary  
> upstream sees it and can divert map-requests to my secondary path.
>
If your primary router goes down, yes.
> So do all of my xTRs need to have ALT tunnels to all of my EID  
> allocators in order to avoid de-aggregation in the ALT tables while  
> maintaining fault tolerant connectivity?
>
All of your xTRs need to connect to the ALT to get mapping  
information. (ie to send
map requests over the ALT and receive map-replies natively).  Each  
xTR would
advertise the same EID-prefix.  So no matter how many xTRs you have,  
only the
single EID-prefix is advertised. The ALT only carries EID-prefix  
routes (and next-hop
information for the ALT).  It need not carry the RLOC routes at all.   
Those are in the DFZ.
> What happens if an AS-wide fault takes down all of my allocator's  
> ALT routers? I understand that my RLOCs are still aggregated by the  
> underlying network's routing regardless.
>
Hopefully you'd have RLOCs from two different allocators.  When one  
goes down, the
other one is still available for map-requests.
>

Hope this helps
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.irtf.org/pipermail/rrg/attachments/20090125/c1a37ccd/attachment.htm>