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

[Mark ZZZ Smith <[e-mail]>]

Hi Michael,


----- Original Message -----
> From: Michael Behringer (mbehring) <[e-mail]>
> To: Brian E Carpenter <[e-mail]>; Mark ZZZ Smith <[e-mail]>
> Cc: Philip Matthews <[e-mail]>; Gert Doering <[e-mail]>; "[e-mail]" <[e-mail]>; Eric Vyncke (evyncke) <[e-mail]>; "[e-mail] list" <[e-mail]>
> 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.

Regards,
Mark.