Re: [netmod] 6991bis: address-with-prefix-length

Kristian Larsson <kristian@spritelink.net> Mon, 01 April 2019 19:40 UTC

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To: "Acee Lindem (acee)" <acee@cisco.com>, Martin Bjorklund <mbj@tail-f.com>
Cc: "j.schoenwaelder@jacobs-university.de" <j.schoenwaelder@jacobs-university.de>, "netmod@ietf.org" <netmod@ietf.org>
References: <20190401161321.seiodlfsmjjvjcp5@anna.jacobs.jacobs-university.de> <F1537180-6BF3-40C7-BCFA-3AAE0290AE9D@cisco.com> <A0F7987F-AA67-4A63-8FEE-3B74B5B47CF1@cisco.com> <20190401.192951.1060904547331848297.mbj@tail-f.com> <4780543F-F233-4874-A5CA-266DCD9C4D70@cisco.com>
From: Kristian Larsson <kristian@spritelink.net>
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Date: Mon, 1 Apr 2019 21:40:09 +0200
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Subject: Re: [netmod] 6991bis: address-with-prefix-length
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On 2019-04-01 19:38, Acee Lindem (acee) wrote:
> 
> ´╗┐On 4/1/19, 1:30 PM, "Martin Bjorklund" <mbj@tail-f.com>; wrote:
> 
>      Hi,
>      
>      The request was for a combined type that contains both an ip address
>      *and* a prefix length in one value.  Hence the name
>      "ip-address-and-prefix-length" :)
> 
> Ok - I understand now.
>      
>      I know that this type is convenient, esp. if you use it for manual
>      input, but I wonder if it really is good practice to squeeze two
>      values into one.
> 
> Agreed. It seems a prefix with a prefix length of 32 for IPv4 or 128 for IPv6 would allow specification.

No, it does not. You must be referring to some other use case. I want to 
configure the IP address and prefix-length on an interface. The 
prefix-length naturally needs to align with the prefix-length / subnet 
mask used on the network to which the interface is connected. If it is a 
/24 network then the prefix-length needs to be 24. I can't just say it's 
a /32 so I can enter this information - the router wouldn't understand 
what is then connected to that network / interface and wouldn't be able 
to route packets correctly.

At the same time, I need to specify the exact IP address to be used by 
this device on the interface, so I need to have bits set to the right of 
the mask, thus I can't use current ip-prefix type.


> The convenience is primarily for mapping to CLI.

Heh, I don't understand what it has to do with CLI but since you're the 
second person mentioning there must be some connection I don't see.

Kind regards,
    Kristian.




>      "Acee Lindem (acee)" <acee@cisco.com>; wrote:
>      > Ok, now I'm confused. I see that the ietf-inet-type model already has the types ipv4-prefix and ipv6-prefix. How are these any different???
>      > Thanks,
>      > Acee
>      >
>      > On 4/1/19, 12:31 PM, "Acee Lindem (acee)" <acee@cisco.com>; wrote:
>      >
>      >     I believe the "address-" could be omitted from the type identifiers. At least within the routing area, "ipv4-prefix" is unambiguous.
>      >     Thanks,
>      >     Acee
>      >
>      >     On 4/1/19, 12:14 PM, "netmod on behalf of Juergen Schoenwaelder" <netmod-bounces@ietf.org on behalf of j.schoenwaelder@jacobs-university.de>; wrote:
>      >
>      >         This is the right time for this and I would call these
>      >         ip-address-prefix, ipv4-address-prefix and ipv6-address
>      >         prefix.
>      >
>      >         /js
>      >
>      >         On Mon, Apr 01, 2019 at 04:38:34PM +0200, Kristian Larsson wrote:
>      >         > Hello,
>      >         >
>      >         > seeing that 6991 is up for a refresh I wonder if this would be the time to
>      >         > suggest the addition of a type for address-and-prefix-length, for example
>      >         > like 192.0.2.1/24?
>      >         >
>      >         > I find that it's the most natural way express the address and prefix-length
>      >         > to configure on an interface or for some other use. We currently have an
>      >         > ip-prefix type which allows CIDR style prefixes but since all bits to the
>      >         > right of the mask is to be 0 it is only possible to use for describing the
>      >         > IP prefix / network address itself - not the address of a host in that
>      >         > network.
>      >         >
>      >         > I actually wish the interface-ip modules would have used a combined leaf for
>      >         > these settings rather than the dual-leaf approach it currently has, but I
>      >         > suppose that ship has sailed :/
>      >         >
>      >         > Regardless, can we add such a type? Is this the document and time to do it?
>      >         > :)
>      >         >
>      >         > Kind regard,
>      >         >    Kristian.
>      >         >
>      >         > _______________________________________________
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>      >
>      >         --
>      >         Juergen Schoenwaelder           Jacobs University Bremen gGmbH
>      >         Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen | Germany
>      >         Fax:   +49 421 200 3103         <https://www.jacobs-university.de/>
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