I have updated the draft to reflect its goal of providing better
identification of the receiving interface to aid in troubleshooting
with traceroute.
There are a few common scenarios that this draft is intended to help
with.
First, the receiving interface may be different than the outgoing
interface (which gives the source IP address in the ICMP packet)
because of either asymmetric link costs or ECMP.
Second, the receiving interface may be unnumbered, so that the source
IP address can't identify the interface. This is a problem for
troubleshooting when there are parallel unnumbered links.
I would welcome any comments or discussion on this draft.
Thanks,
Alia
On 5/15/07, *Alia Atlas* <akatlas at gmail.com
<mailto:akatlas at gmail.com>> wrote:
On 5/14/07, *Pekka Savola* <pekkas at netcore.fi
<mailto:pekkas at netcore.fi>> wrote:
On Mon, 14 May 2007, Alia Atlas wrote:
> In general, I find the specification having features that I
don't see
>> necessary. Reporting ifIndex is not necessary (and the
index is not
>> very useful as is to a human) if ifName is
reported. Addresses are
>> already known from the source address though somewhat less
reliably so
>> those need not be reported for outgoing interface use, and
could also
>> result in reporting IPv6 link-local addresses (or IPv4
private
>> addresses) which wouldn't necessarily be useful or desired.
>
> The idea with reporting the ifIndex is to provide the easy
ability
> to correlate that to MIB data. It is a common look-up key
and I
> believe it to be useful.
>
> Using simply the source address doesn't handle topologies with
> parallel links between routers. In that case, knowing the
exact
> outgoing link for troubleshooting is useful. ...
(A potentially interesting note: at least one implementation
has an
internal 'interface index' which is different from 'SNMP
ifIndex'.
The intent should be clear in the spec.)
Do you have improved phrasing you might suggest?
If ifName is reported, is there significant benefit in reporting
ifIndex as well?
It could be more easily used for correlation, but that's only
useful
for the operators of the network who could know the ifIndexes
on the
routers, not outsiders. On the other hand, those network
operators
can very well map the ifName to ifIndex using SNMP or similar
tools as
well.
True - I guess some of it depends whether the name or ifIndex is
more private
and how many steps an operator has to take to get decent results.
On the other hand, normal traceroute gives both the IP address and
the DNS
name, if any. I was looking to provide the equivalent.
I'm not strongly against being able to report ifIndex (but I'd
rather
that it doesn't get reported by default, at least to
everyone), but it
seems like a feature that's more likely to clutter the traceroute
output with little added value: ifName should already provide
the same
benefits and is a more generic mechanism.
All of the additional info is optional and an operator could
determine what
to show based upon the incoming IP address or such.
Again, I was going for duplicating the information provided if an
IP address existed.
Alia
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