[175146] in North American Network Operators' Group
Re: IPv6 Default Allocation - What size allocation are you giving out
daemon@ATHENA.MIT.EDU (Baldur Norddahl)
Thu Oct 9 16:25:18 2014
X-Original-To: nanog@nanog.org
In-Reply-To: <B459E914-CA83-4ECB-8663-61F8EED2FDEC@delong.com>
Date: Thu, 9 Oct 2014 22:25:10 +0200
From: Baldur Norddahl <baldur.norddahl@gmail.com>
To: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
On 9 October 2014 22:01, Owen DeLong <owen@delong.com> wrote:
> > Why do people assign addresses to point-to-point links at all? You can
> just
> > use a host /128 route to the loopback address of the peer. Saves you the
> > hassle of coming up with new addresses for every link. Same trick works
> for
> > IPv4 too.
> >
> > Regards,
> >
> > Baldur
>
> <SARCASM>
>
> And it makes your trace-routes across parallel links oh so easy to
> identify which of them is at fault for the packet loss, too.
>
> </SARCASM>
>
There are a ton of other technologies with the same problem. Do you never
use link aggregation? My "parallel links" are all link aggregations, so I
would not have a way to identify links by traceroute anyway.
There are a number of good technical reasons to want distinct addresses on
> point to point links.
>
I am sure there are. Tell me about them.
I am not disputing that there are many reasons to sometimes use link
addresses. My question is why do you do it by default?
So far we have heard two arguments:
1) You can ping the link address. I assume his equipment will down the
address if the link is down. My equipment does not do this, I can ping it
as long it is administrative up no matter link status. So this test is
useless to me. I am monitoring links by SNMP anyway.
2) Parallel links. I don't have many of those, and the ones I have are link
aggregations. MPLS interferes with this too.
On the other hand not using link addresses has some advantages:
1) You don't need to assign and document them.
2) It is easy to think about: Router A talks to Router B on link AB. Every
router has only one address so you don't need to remember which address to
use.
3) You avoid having a lot of addresses configured on your router.
4) You are immune to all the NDP attacks.
5) You are immune to the monthly NANOG debate about using /127 vs /126 vs
/124 vs /64. The correct answer is clearly use /128 :-).
Regards,
Baldur
