Hi. /31 on ethernet links

[Sebastian Hyrwall-2]

Hi.


Is there any way to use /31's on ordinary ethernet links in 7.2?
"ifconfig addr dest-addr" does not work either. It keeps setting the
last ip as broadcast.


Sincerley,
Sebastian H
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[Chuck Swiger-2]

On Oct 30, 2009, at 4:46 PM, Sebastian Hyrwall wrote:
> Is there any way to use /31's on ordinary ethernet links in 7.2?  
> "ifconfig addr dest-addr" does not work either. It keeps setting the  
> last ip as broadcast.

A /31 subnet is only defined for point-to-point network links, per:

   http://www.rfc-editor.org/rfc/rfc3021.txt

Ordinary ethernet links have BROADCAST flag set instead of POINTOPOINT.

Regards,
--
-Chuck

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[Sebastian Hyrwall-2]

Chuck Swiger skrev:

> On Oct 30, 2009, at 4:46 PM, Sebastian Hyrwall wrote:
>> Is there any way to use /31's on ordinary ethernet links in 7.2?
>> "ifconfig addr dest-addr" does not work either. It keeps setting the
>> last ip as broadcast.
>
> A /31 subnet is only defined for point-to-point network links, per:
>
>   http://www.rfc-editor.org/rfc/rfc3021.txt
>
> Ordinary ethernet links have BROADCAST flag set instead of POINTOPOINT.
>
> Regards,

Well how do I set the POINTOPOINT flag and remove the BROADCAST-flag on
ethernet links? Or are you implying that it does not belong on ethernet
links :)
Cause Cisco and Linux support /31 (ptp's) on ordinary ethernet links.

Sincerely,
Sebastian H
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[Freddie Cash-8]

Reading the man page for ifconfig will show the "ptp" option for ifconfig,
that configures the interface as a point-to-point interface..  :)



On Fri, Oct 30, 2009 at 5:22 PM, Sebastian Hyrwall <sh@...> wrote:

> Chuck Swiger skrev:
>
>> On Oct 30, 2009, at 4:46 PM, Sebastian Hyrwall wrote:
>>
>>> Is there any way to use /31's on ordinary ethernet links in 7.2?
>>> "ifconfig addr dest-addr" does not work either. It keeps setting the last ip
>>> as broadcast.
>>>
>>
>> A /31 subnet is only defined for point-to-point network links, per:
>>
>>  http://www.rfc-editor.org/rfc/rfc3021.txt
>>
>> Ordinary ethernet links have BROADCAST flag set instead of POINTOPOINT.
>>
>> Regards,
>>
> Well how do I set the POINTOPOINT flag and remove the BROADCAST-flag on
> ethernet links? Or are you implying that it does not belong on ethernet
> links :)
> Cause Cisco and Linux support /31 (ptp's) on ordinary ethernet links.
>
> Sincerely,
>
> Sebastian H
> _______________________________________________
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>

--
Freddie Cash
fjwcash@...
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[Sebastian Hyrwall-2]

Freddie Cash skrev:
> Reading the man page for ifconfig will show the "ptp" option for
> ifconfig, that configures the interface as a point-to-point
> interface..  :)
>

It will also show that it seems to be only for bridgeing,

# ifconfig  fxp0 ptp fxp0
ifconfig: unable to get bridge flags: Invalid argument

>
>
> On Fri, Oct 30, 2009 at 5:22 PM, Sebastian Hyrwall <sh@...
> <mailto:sh@...>> wrote:
>
>     Chuck Swiger skrev:
>
>         On Oct 30, 2009, at 4:46 PM, Sebastian Hyrwall wrote:
>
>             Is there any way to use /31's on ordinary ethernet links
>             in 7.2? "ifconfig addr dest-addr" does not work either. It
>             keeps setting the last ip as broadcast.
>
>
>         A /31 subnet is only defined for point-to-point network links,
>         per:
>
>          http://www.rfc-editor.org/rfc/rfc3021.txt
>
>         Ordinary ethernet links have BROADCAST flag set instead of
>         POINTOPOINT.
>
>         Regards,
>
>     Well how do I set the POINTOPOINT flag and remove the
>     BROADCAST-flag on ethernet links? Or are you implying that it does
>     not belong on ethernet links :)
>     Cause Cisco and Linux support /31 (ptp's) on ordinary ethernet links.
>
>     Sincerely,
>
>     Sebastian H
>     _______________________________________________
>     freebsd-net@... <mailto:freebsd-net@...> mailing list
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>     <mailto:freebsd-net-unsubscribe@...>"
>
>
>
>
> --
> Freddie Cash
> fjwcash@... <mailto:fjwcash@...>

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[Chuck Swiger-2]

On Oct 30, 2009, at 5:22 PM, Sebastian Hyrwall wrote:

>> A /31 subnet is only defined for point-to-point network links, per:
>>
>>  http://www.rfc-editor.org/rfc/rfc3021.txt
>>
>> Ordinary ethernet links have BROADCAST flag set instead of  
>> POINTOPOINT.
>>
>
> Well how do I set the POINTOPOINT flag and remove the BROADCAST-flag  
> on ethernet links? Or are you implying that it does not belong on  
> ethernet links :)  Cause Cisco and Linux support /31 (ptp's) on  
> ordinary ethernet links.

Ethernet point-to-point links are normally handled by ppp / pppd in  
PPPoE mode, but possibly something like:

   ifconfig en0 inet 192.1.1.10 inet 192.1.1.2

...would give you a POINTOPOINT link instead.  If not, you can  
probably fake things out by either using a /30 and wrapping the /31  
inside, or using  a /32 and an explicit default route via your  
ethernet interface.

Regards,
--
-Chuck

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[Chuck Swiger-2]

On Oct 30, 2009, at 3:37 PM, Chuck Swiger wrote:
>  ifconfig en0 inet 192.1.1.10 inet 192.1.1.2

Whoops-- copy-paste-typo; instead should be:

   ifconfig en0 inet 192.1.1.10 192.1.1.11

--
-Chuck

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[Sebastian Hyrwall-2]

Chuck Swiger skrev:

> On Oct 30, 2009, at 5:22 PM, Sebastian Hyrwall wrote:
>>> A /31 subnet is only defined for point-to-point network links, per:
>>>
>>>  http://www.rfc-editor.org/rfc/rfc3021.txt
>>>
>>> Ordinary ethernet links have BROADCAST flag set instead of POINTOPOINT.
>>>
>>
>> Well how do I set the POINTOPOINT flag and remove the BROADCAST-flag
>> on ethernet links? Or are you implying that it does not belong on
>> ethernet links :)  Cause Cisco and Linux support /31 (ptp's) on
>> ordinary ethernet links.
>
> Ethernet point-to-point links are normally handled by ppp / pppd in
> PPPoE mode, but possibly something like:
>
>   ifconfig en0 inet 192.1.1.10 inet 192.1.1.2
>
> ...would give you a POINTOPOINT link instead.  If not, you can
> probably fake things out by either using a /30 and wrapping the /31
> inside, or using  a /32 and an explicit default route via your
> ethernet interface.
>

Unfortunetly that doesn't work. It just sets 192.1.1.2 as broadcast.

Well wrapping a /31 inside of a /30 kinda defeats the purpose :)


If Cisco,Linux and NetBSD support it so should FreeBSD imho.

> Regards,

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[randyb]

/31 on point to point ether is exceedingly common in inter-router
topologies.

you may be amused to also read draft-kohno-ipv6-prefixlen-p2p-00.txt

randy
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[sthaug]

> > A /31 subnet is only defined for point-to-point network links, per:
> >
> >   http://www.rfc-editor.org/rfc/rfc3021.txt
> >
> > Ordinary ethernet links have BROADCAST flag set instead of POINTOPOINT.
> >
> > Regards,
> Well how do I set the POINTOPOINT flag and remove the BROADCAST-flag on
> ethernet links? Or are you implying that it does not belong on ethernet
> links :)
> Cause Cisco and Linux support /31 (ptp's) on ordinary ethernet links.

No, Cisco does not *support* it. They make it available, which is a
completely different story.

We have asked Cisco repeatedly, through official channels, whether
they *support* /31 on Ethernet links. The answer is always that it
*may* work, use at your own peril.

Steinar Haug, Nethelp consulting, sthaug@...
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[randyb]

> No, Cisco does not *support* it. They make it available, which is a
> completely different story.
>
> We have asked Cisco repeatedly, through official channels, whether
> they *support* /31 on Ethernet links. The answer is always that it
> *may* work, use at your own peril.

i have managed O(10^3) ciscos in isp backbone(s).  /31s predominate for
ether links in that space.  though i suspect there is more multipoint in
the enterprise space.

we need to be able to use /31s and /127s on freebsd if it is to be used
in the routing space.

randy
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[sthaug]

> > We have asked Cisco repeatedly, through official channels, whether
> > they *support* /31 on Ethernet links. The answer is always that it
> > *may* work, use at your own peril.
>
> i have managed O(10^3) ciscos in isp backbone(s).  /31s predominate for
> ether links in that space.  though i suspect there is more multipoint in
> the enterprise space.
>
> we need to be able to use /31s and /127s on freebsd if it is to be used
> in the routing space.

I agree about that.

However, I was simply reacting to the claim that it was *supported* by
Cisco. We have asked both Cisco and Juniper, and neither company is
willing to state that it is *supported*. Our Ethernet core links are
/30 for IPv4 and /124 for IPv6.

Steinar Haug, Nethelp consulting, sthaug@...
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[randyb]

> However, I was simply reacting to the claim that it was *supported* by
> Cisco.

have you noticed a difference in the bug rate between things that are
'supported by cisco' and those that just happen to be there?  :)

but you're right.  i liked.  our p2ps are /30s, not /31s.  and we're
moving from /126 to /127.

randy
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[Nikos Vassiliadis-5]

Sebastian Hyrwall wrote:
> Chuck Swiger skrev:
>> inside, or using  a /32 and an explicit default route via your
>> ethernet interface.
>>
> Unfortunetly that doesn't work. It just sets 192.1.1.2 as broadcast.
>
> Well wrapping a /31 inside of a /30 kinda defeats the purpose :)
>

You could still use a /32 and then add a route for the other IP via
the ethernet interface. This is effectively the same with a /31.

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[Sebastian Hyrwall-2]

Nikos Vassiliadis skrev:

> Sebastian Hyrwall wrote:
>> Chuck Swiger skrev:
>>> inside, or using  a /32 and an explicit default route via your
>>> ethernet interface.
>>>
>> Unfortunetly that doesn't work. It just sets 192.1.1.2 as broadcast.
>>
>> Well wrapping a /31 inside of a /30 kinda defeats the purpose :)
>>
>
> You could still use a /32 and then add a route for the other IP via
> the ethernet interface. This is effectively the same with a /31.
>

Does not work,

# ifconfig re0.212 172.16.25.10 netmask 255.255.255.255
# route add 172.16.25.11 -iface re0.212
add host 172.16.25.11: gateway re0.212
# ping 172.16.25.11
36 bytes from 172.16.25.10: Redirect Host(New addr: 172.16.25.11)
Vr HL TOS  Len   ID Flg  off TTL Pro  cks      Src      Dst
 4  5  00 0054 bdbb   0 0000  40  01 0000 172.16.25.10  172.16.25.11




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[Bjoern A. Zeeb]

On Sat, 31 Oct 2009, Randy Bush wrote:

Hi,

>> However, I was simply reacting to the claim that it was *supported* by
>> Cisco.
>
> have you noticed a difference in the bug rate between things that are
> 'supported by cisco' and those that just happen to be there?  :)
>
> but you're right.  i liked.  our p2ps are /30s, not /31s.  and we're
> moving from /126 to /127.

I am sorry, I couldn't resist; I hope you won't take everything at
face value... though I hope you'll seriously think of some things...

Oh what /30 /31 bikeshed and how old it is?

I prefer to speak of p_t_p for point-to-point  in contrast to p2p for
peer-2-peer btw.  I seem to remember that it used to be like that but
unfortunately neither the vendors nor the people who are writing
(IETF) specs make a difference anymore.

I do not understand, though I know some, people who are not using a
/64 on an Ethernet IPv6 link; may it be ptp or not.  I know there is
an old enough bikeshed out about that as well as some prosposed
standards.  /127 really sounds fighting a system to me.
It's not that you couldn't address each atom in hour house already I'd
wildy guess with a /48 but ... some people always have trouble freeing
their mind from things that were like that 20 years and further back.
Have you ever thought of limiting your scoped link-local space on
Ethernet?  So why do you need valid IPs on your interfaces at all?
Why do you need more than a single global unicast address? Save your
IPv6 addresses for the neighbour's fridges and toasters.

/bz

--
Bjoern A. Zeeb       Even on Oct. 31st there is no candy with this mail.
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[Nikos Vassiliadis-5]

Sebastian Hyrwall wrote:
>> You could still use a /32 and then add a route for the other IP via
>> the ethernet interface. This is effectively the same with a /31.
>>
> Does not work,

I see, I've checked this on 9.0 and found it working, not on 7.2.

Nikos

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