Re: [v6ops] about LLAs pros/cons static routing - auto/self-configuration of addresses, draft-matthews-v6ops-design-guidelines

> there is no GUA/ULA configured on the interface, then the router sends the
> ICMP reply using the IP address of the loopback or system address as the
> source address. 

Stating the obvious assumption - Loopback interface is configured with GUA/ULA.

Cheers,
Rajiv

> -----Original Message-----
> From: v6ops-bounces@ietf.org [mailto:v6ops-bounces@ietf.org] On Behalf
> Of Philip Matthews
> Sent: Thursday, August 09, 2012 5:58 PM
> To: Mark ZZZ Smith
> Cc: v6ops@ietf.org list; Michael Behringer (mbehring)
> Subject: Re: [v6ops] about LLAs pros/cons static routing - auto/self-
> configuration of addresses, draft-matthews-v6ops-design-guidelines
> 
> 
> On 2012-08-09, at 17:39 , Mark ZZZ Smith wrote:
> 
> > Hi Michael,
> >
> >
> > ----- Original Message -----
> >> From: Michael Behringer (mbehring) <mbehring@cisco.com>
> >> To: Brian E Carpenter <brian.e.carpenter@gmail.com>; Mark ZZZ Smith
> >> <markzzzsmith@yahoo.com.au>
> >> Cc: Philip Matthews <philip_matthews@magma.ca>; Gert Doering
> >> <gert@space.net>; "sthaug@nethelp.no" <sthaug@nethelp.no>; Eric
> >> Vyncke (evyncke) <evyncke@cisco.com>; "v6ops@ietf.org list"
> >> <v6ops@ietf.org>
> >> Sent: Thursday, 9 August 2012 9:08 PM
> >> Subject: RE: [v6ops] about LLAs pros/cons static routing -
> >> auto/self-configuration of addresses,
> >> draft-matthews-v6ops-design-guidelines
> >>
> >>>> Traceroute would work for you,
> >>>
> >>> It shouldn't, because intermediate routers should discard ICMPv6
> >> packets
> >>> with LL source addresses, according to RFC 4291 section 2.5.6.
> >>>
> >>> The fact that they don't is an implementation error, and we
> >> shouldn't rely
> >>> on that. ICMPv6 should never be sourced from a LL address.
> >>
> >> I can confirm that at least one implementation (ours) responds using
> >> a global address (from a loopback), not the link local.
> >>
> >>>
> >>>      Brian
> >>>
> >>> however outside of your network, other people would be querying
> >>> their own version of 0.8.e.f.ip6.arpa., hiding your interface and router
> names.
> >>> This idea might be useful to assist with troubleshooting for a
> >>> "Using
> >> Only
> >>> Link-Local Addressing Inside an
> >>> IPv6 Network" http://tools.ietf.org/html/draft-behringer-lla-only-01
> >>> scenario.
> >>
> >> The concern is that for ICMP echo reply, traceroute, etc the router
> >> will respond with a global address, which is a loopback address (in
> >> the absence of global addresses on the interface). You can therefore
> >> see the router, but not the interface (unless RFC5837 is implemented,
> >> which is generally not the case today).
> >>
> >> So I can't see how this helps troubleshooting? (I must be
> >> misunderstanding something here)
> >
> > As Brian said, traceroute won't reliably work due to the LL source address
> issue, however having unique static LL addresses across your network's
> router interfaces, and then having a record of the static LL address
> assignments in 0.8.e.f.ip6.arpa via PTRs (and perhaps TXTs for
> supplementary information) might still be a useful troubleshooting tool. For
> example, if you're on the CLI of one router, and want to find out the
> interface name corresponding to an adjacent router's static LL address, a
> ping command with a reverse resolve of the address far router's interface
> address would return the result of the PTR and therefore the name of the
> remote interface and router.
> 
> I believe traceroute will work.  As Michael said, at least some routers, if
> there is no GUA/ULA configured on the interface, then the router sends the
> ICMP reply using the IP address of the loopback or system address as the
> source address. Michael confirmed that Cisco routers work this way, and I
> can confirm that Alcatel-Lucent routers work this way.
> 
> If anyone knows of a router which behaves differently, I would be
> interested in hearing of it. This would be a useful comment to put in my I-D.
> 
> - Philip
> 
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