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Re: loopback /32 mask

  • From: Eric Osborne <eosborne@cisco.com>
  • Date: Sat, 17 Mar 2001 23:11:02 -0500
  • Cc: "'rcheung@slb.com'" <rcheung@slb.com>, MPLS Mailing List <mpls-ops@mplsrc.com>
  • Resent-Date: Sun, 18 Mar 2001 00:26:33 -0500
  • To: "Martin, Christian" <cmartin@gnilink.net>
  • User-Agent: Mutt/1.2.5i
  • X-GPG-Fingerprint: 6412 0836 E440 B3EA 980C 4951 611E 1819 2E71 8562

On Sat, Mar 17, 2001 at 07:30:25PM -0500, Martin, Christian wrote:
> Because anything larger would waste addresses.  Were you to use, say, a 24
> bit mask on a loopback, then every address in that range would be reachable
> via the loopback.  If you wish to waste IP space, then use shorter masks.
> 

The MPLS reason for that is more fundamental.  If you have a mask
other than /32 for the next-hop of a route you're going to use MPLS to
get to then you can't guarantee that that route didn't come from a
summary at some point.  And this is a problem with VPN, as you have no 
way to know where to forward the packet if you have to do a
de-aggregate lookup.

The specs, I believe, require a /32 for both BGP next-hop for a VPN
route and for TE tunnel endpoints.  Last I checked, our implementation 
only enforced this for VPN routes; I could be wrong, tho.


eric

> regards,
> chris
> 
> > -----Original Message-----
> > From: Raymond Cheung [mailto:rcheung@slb.com]
> > Sent: Saturday, March 17, 2001 5:56 PM
> > To: MPLS Mailing List
> > Subject: loopback /32 mask
> > 
> > 
> > Any particular reason for loopback to be /32 mask during 
> > RSVP-TE config? I
> > understand it's good to have loopback as router id or 
> > headend, or ..., but
> > my question is, is it mandatory that the mask should be /32? 
> > why other masks
> > won't work?
> > regards,
> > 
> > ================================================
> > Yinglam (Raymond) Cheung
> > Schlumberger Network Solutions
> > CCIE (R/S), CCNP+ATM, CCDP
> > Tel: (713) 513-3285
> > 5599 San Felipe St Suite 400
> > Houston, TX 77056
> > Email: rcheung@slb.com
> > ================================================
> > 
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