> I think you'll find that that's not really the case.
>
> /30's are still quite the rage in the service provider world,
> though ip un-number works well enough for the customer attach
> access-router application.
IP Unnumbered is used by ISPs in the world. The use of /30s is more of a
ignorance of the scaling impact.
> Too bad Cisco can't embrace the /31. 8-)
Please check out the ID -> "Using 31-Bit Prefixes on IPv4 Point-to-Point
Links" (draft-retana-31bits-01.txt). It is strange that you get this
impression when two of the co-authors are from Cisco.
Check out CSCdk17555. /31 was implemented in 12.0(13.01)S. We're working on
getting it into 12.1E for the CAT6K/OSR (to hold us until 12.2S comes out).
For those of you new to /31, it has the advantages of the troubleshoot
utility of a /30 and the address conservation people look for in IP
Unnumbered. For example:
|
+------+ lan1 (10.0) +------+
| |-------------| |
| 75a |-------------| 75b |
+------+ lan2 (200) +------+
| |
31 bit / |
| |
lan3(70.10/31) |lan5 (50.0)
+------+ +------+
| 7ka | lan4 (40.0)| 45b |
| |-------------| |
+------+ +------+
The serial link between router 75a and router 7ka is using a /31. The serial
interface config on router 75a looks like:
interface Serial5/1
bandwidth 1544
ip address 145.10.70.2 255.255.255.254
no ip directed-broadcast
no ip mroute-cache
!
and on router 7ka it looks like:
interface Serial6/3
bandwidth 1544
ip address 145.10.70.3 255.255.255.254
no ip directed-broadcast
no ip mroute-cache
!
In a few months, we'll be recommending /31 as BCP in the ISP Essentials and
ISP Workshop materials. We'll need to get it rolled into the baseline before
we do that. That way we can recommend this BCP for ISPs on 2500 based
backbones as well as ISPs with CAT6Ks, ESRs, and GSRs. We also need some
more field experience with /31. No scaling consensus of whether we put it
into the IGP or iBGP. In the mean time, /31 is only on 12.0S for the 7200,
7500, and GSR.
Given this, I would say Cisco has embraced /31. Of course I'm also blatantly
biased. ;-)
Barry
This archive was generated by hypermail 2b29 : Sun Aug 04 2002 - 04:12:27 EDT