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

Mark Smith <markzzzsmith@gmail.com> Thu, 09 February 2017 19:26 UTC

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From: Mark Smith <markzzzsmith@gmail.com>
Date: Fri, 10 Feb 2017 06:26:02 +1100
Message-ID: <CAO42Z2wuibtYx39tJFAKJ=TdcWLe8tCQHz9YSbaeUHFyJSb8rw@mail.gmail.com>
Subject: Re: [IPv6 SR] Regarding 128 bits IPv6 address in Segment List of SRH
To: Veerendranatha Reddy Vallem <veerendranatharv@huawei.com>
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On 10 Feb. 2017 03:02, "Veerendranatha Reddy Vallem" <
veerendranatharv@huawei.com> wrote:

Dear Authors,

I am requesting your clarification regarding usage of Adj-SID in SRH header.



As per draft, the segment list  is the list of 128 bit IPv6 address.

Whether it means it is global ipv6 address or can be link local address also.



As per “OSPFv3 Extensions for Segment Routing” draft, the Adj-SID can
be link local address.

In section 7.1,





    0                   1                   2                   3

    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |               Type            |              Length           |

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   | Flags         |     Weight    |             Reserved          |

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   |                   SID/Label/Index (variable)                  |

   +---------------------------------------------------------------+



Examples:



            A 32 bit global index defining the offset in the SID/Label

            space advertised by this router - in this case the V and L

            flags MUST NOT be set.



            A 24 bit local label where the 20 rightmost bits are used

            for encoding the label value - in this case the V and L

            flags MUST be set.



            16 octet IPv6 address - in this case the V-flag MUST be set.

            *The L-flag MUST be set for link-local IPv6 address* and MUST

            NOT be set for IPv6 global unicast address.



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.

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 “global
ipv6 interface address” of the neighbor on the link?



Regards,

Veerendranath





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