Re: [Autoconf] new charter

Carlos Jesús Bernardos Cano <cjbc@it.uc3m.es> Sat, 28 February 2009 13:24 UTC

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From: Carlos =?ISO-8859-1?Q?Jes=FAs?= Bernardos Cano <cjbc@it.uc3m.es>
To: Alexandru Petrescu <alexandru.petrescu@gmail.com>
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Date: Sat, 28 Feb 2009 14:24:26 +0100
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Subject: Re: [Autoconf] new charter
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Hi Alex,

	Sorry for the late reply, trying to catch up now...

El vie, 27-02-2009 a las 11:08 +0100, Alexandru Petrescu escribió:
> Carlos Jesús Bernardos Cano a écrit :
> > Hi Alex:
> > 
> > One question below.
> > 
> > El jue, 26-02-2009 a las 20:44 +0100, Alexandru Petrescu escribió:
> >> Sorry, I made an error indeed putting same prefix.  How about this
> >>  updated picture with the prefixes being distinct:
> >> 
> >> 
> >> -----  wifi "adhoc1"  ------  wifi "adhoc2"  ----- 
> >> |Host1|---------------|Router|---------------|Host2| ----- LL1
> >> LL2 ------ LL3        LL4  ----- G1
> >> G4
> >> 
> >> 
> >> "adhoc1" and "adhoc2": 802.11 ESSIDs in "ad-hoc" mode. Each is an
> >> IPv6 subnet. LL1...4: IPv6 link-local addresses. Self-formed
> >> according to rfc2464. G1, G4:  IPv6 global addresses, for example 
> >> 2001:db8:1::1/64 and 2001:db8:2::4/64 Manually assigned, or
> >> pre-configured with SNMP or formed according to stateless autoconf
> >> rfc4862; the prefixes are advertised by Router in RAs.
> >> 
> > 
> > Does this model only apply to Host-Router-Host scenarios?
> 
> Yes.
> 
> > I mean, does this model apply for Router-Router-Router scenarios?
> 
> Something like this?:
> 
>         -------  wifi "adhoc1"  -------  wifi "adhoc2"  -------
>        |Router1|---------------|Router2|---------------|Router3|
>         ------ LL1          LL2 -------LL3          LL4 -------
>                G1                                    G4
> 
>        G1, G4: ?
> 
> > I fully agree the model fits the first scenario, but I don't for the
> >  second, since routers' mobility within the ad-hoc network would
> > force them to change prefixes often, I guess.
> 
> Ah.  But before being forced to change a prefix, a Router could still
> move around as much as it wants.  I think the limit is within 25m range,
> as imposed by the wifi 50m area (25m for two routers in opposite
> directions).  What do you think about this practical limit?

Well, this is tipically the range for 802.11bg (.11a can even less, .11p
is more). It's a matter of the scenario we consider to asusume that this
range is enough for a router (i.e. it will not move further). Anyway,
due to the characteristics of the wireless and unmanaged nature of
MANETs, it might be the case that even without movement routers need to
change addresses (think of your pictur above in which Router2 is turned
off).

> 
> > For those scenarios it might be better to think of addressing models
> > in which MANET routers are configured with /128 (or /32 for IPv4)
> > addresses, so they don't need to change their addresses as a result
> > of link changes.
> 
> Sorry... in the picture above the addresses are also /128.  It was an 
> abbreviation for me to show only 2001:db8:1::1/64 assigned to Host1. 
> The full notation should have been 2001:db8:1::/64 prefix and 
> 2001:db8:1::1/128.  Would the following picture satisfy the need for 
> /128 addresses?:
> 
>          -----  wifi "adhoc1"  ------  wifi "adhoc2"  -----
>         |Host1|---------------|Router|---------------|Host2|
>          ----- LL1    P1   LL2 ------ LL3   P2   LL4  -----
>                G1                                G4
> 
>         G1, G4:  IPv6 global addresses, for example
>                  2001:db8:1::1/128 and
>                  2001:db8:2::4/128
>                  Manually assigned, or pre-configured with SNMP
>                  or formed according to stateless autoconf rfc4862;
>                  the prefixes are advertised by Router in RAs.
>         P1, P2:  IPv6 global prefixes, for example
>                  2001:db8:1::/64 and
>                  2001:db8:2::/64
>                  Manually assigned, or pre-configured with SNMP.
> 
> 
> Or is it not what you mean?

Yes, more ore less, but I think I agree with Teco in which I'd assign
those /128 addresses to loopback (not physical) interfaces.

> 
> I also don't understand why you think that if /128 addresses are 
> assigned to routers then they don't need to change them as a result of 
> link changes.

This is because in my understanding a /128 address cannot be formed
according ti rfc4862 (only /64 can). If the router gets a /128 address
by any other means, the MANET routing protocol would take care of
ensuring this address isreachable despite the movement of the router. 

Carlos

> 
> Alex
> 
> 
-- 
 Carlos Jesús Bernardos Cano     http://www.netcoms.net
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