Subject: [IPFIX] ipNextHopIPv6Address reported address

From: Nick Brown <[email-masked]>
Date: Thu, 4 Jun 2015 11:07:19 +0000

Hi All,

In a sentence, is it expected that ipNextHopIPv6Address should report
the global ipv6 address of the next hop when it has one, or may the link
local address be reported instead?
http://tools.ietf.org/html/rfc5102#section-5.7.3

There are obvious cases where the next hop may only have link local
address, if example it's only configured that way. But in other cases
where it may have both a link local and global address it's often the
case that routing protocols may use local addresses to setup the
forwarding plane where traffic is being observed. Thus at the point in
the forwarding path that traffic is being observed this all that is
available, and it's not apparent that a mapping from link local address
to global address (where is exists) can be done.

Cheers,
Nick

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From: Brian Trammell <[email-masked]>
Date: Thu, 4 Jun 2015 15:47:21 +0200

> On 04 Jun 2015, at 13:07, Nick Brown <[email-masked]> wrote:
> 
> Hi All,
> 

First, the proper reference for the definitions of IEs in the IPFIX information model is http://www.iana.org/assignments/ipfix/ipfix.xhtml; per 7012, 5102 is no longer considered authoritative for IE definitions.

(In this case, though, this is an admittedly pedantic distinction; the content is identical).

> to global address (where is exists) can be done.

The way I read this, if the address is not being changed as part of the packet handing (on which see the fifth point in section 2.3 of RFC 7012), the address to report is the address the packets are sent to in the context of the egress interface. If the connection between the device the MP is on and the next hop has link-local addresses only, then the link-local address is the correct one to export.

Cheers,

Brian

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From: Nick Brown <[email-masked]>
Date: Mon, 8 Jun 2015 13:04:21 +0000

> The way I read this, if the address is not being changed as part of the packet handing (on which see the fifth point in section 2.3 of RFC 7012), the address to report is the address the packets ar…

ipNextHopIPv6Address is a derived field, derived from the treatment of
the packet by the switching path that constitutes our Observation point.
While at the global network level and possibly at the configuration
level of the IPFIX Device's Metering Process the interface of the Next
Hop may have both a link local IPV6 address and global IPV6 address, the
only one readily available to the Metering Process is the link local
address used by the switching path to do it's work, so that is what we
report.

Cheers,
Nick