Re: [OSPF] [IPv6 SR] Regarding 128 bits IPv6 address in Segment List of SRH

"Acee Lindem (acee)" <acee@cisco.com> Thu, 09 February 2017 23:41 UTC

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From: "Acee Lindem (acee)" <acee@cisco.com>
To: Brian E Carpenter <brian.e.carpenter@gmail.com>, Mark Smith <markzzzsmith@gmail.com>, Veerendranatha Reddy Vallem <veerendranatharv@huawei.com>
Subject: Re: [OSPF] [IPv6 SR] Regarding 128 bits IPv6 address in Segment List of SRH
Thread-Topic: [OSPF] [IPv6 SR] Regarding 128 bits IPv6 address in Segment List of SRH
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Date: Thu, 9 Feb 2017 23:41:12 +0000
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On 2/9/17, 5:48 PM, "OSPF on behalf of Brian E Carpenter"
<ospf-bounces@ietf.org on behalf of brian.e.carpenter@gmail.com> wrote:

>Mark,
>On 10/02/2017 08:26, Mark Smith wrote:
>> On 10 Feb. 2017 03:02, "Veerendranatha Reddy Vallem" <
>> veerendranatharv@huawei.com> wrote:
>...
>>> If Link local address is Link local, how we can use this address in
>>>SRH header, 
>>> since IPv6 destination address should not be link local address as per
>>> IPv6 protocol.
>> 
>> I'd be curious where you might have got that idea from.
>> LL addresses are perfectly fine as destination addresses, including for
>> application traffic. They're even preferred over global and ULA
>>addresses
>> by default when there is a choice from a set.
>
>Right, but if an SR header is travelling off-link, which I think must
>often
>be the case, it would be doubleplus ungood to include a LL address, which
>is
>meaningless off-link. So probably using a LL address in SRH needs to be
>strictly limited.

Agreed - even though the the link-local address is associated with the
OSPFv3 router¹s adjacency, in the IPv6 SR header there is no indication of
outgoing interface so the IPv6 packet cannot be forwarded unambiguously.
Note that we have a similar restriction for OSPFv3 AS-External-LSA and
NSSA-LSA forwarding address. From RFC 5340:


   Forwarding address
      A fully qualified IPv6 address (128 bits).  Included in the LSA if
      and only if bit F has been set.  If included, data traffic for the
      advertised destination will be forwarded to this address.  It MUST
      NOT be set to the IPv6 Unspecified Address (0:0:0:0:0:0:0:0) or an
      IPv6 Link-Local Address (Prefix FE80/10).  While OSPFv3 routes are
      normally installed with link-local addresses, an OSPFv3
      implementation advertising a forwarding address MUST advertise a
      global IPv6 address.  This global IPv6 address may be the next-hop
      gateway for an external prefix or may be obtained through some
      other method (e.g., configuration).


The OSPFv3 Segment Routing Extensions draft will be updated to correct
this. 

Thanks,
Acee


>
>   Brian
>
>> Many of the advantages of LLs for end-user applications would also
>>apply to
>> network applications such as SR.
>> 
>> "How to use IPv6 Link-Local Addresses in Applications"
>> https://tools.ietf.org/html/draft-smith-ipv6-link-locals-apps-00
>> 
>> Regards,
>> Mark.
>> 
>> 
>> 
>> If Adj-Sid is global ipv6 address, means we need to consider ³global
>> ipv6 interface address² of the neighbor on the link?
>> 
>> 
>> 
>> Regards,
>> 
>> Veerendranath
>> 
>> 
>> 
>> 
>> 
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