Subject: Re: [mif] Five additional problem statements for mif----Different metric measurements

From: Min Hui <[email-masked]>
Date: Wed, 18 Mar 2009 11:52:21 +0800

Hi, all

This is the third one: Different metric measurements

Metrics are used to measure the performance of routings, the lower
metric it owns, the higher priority it has. For example, the default
gateway is chosen based on the metric rule as RFC1122 description, The
one have the lowest metric value becomes to the default gateway among
several connected gateways, and the interface correspond to this
gateway turns to be the default interface.
Metric rules are different depending on the access technology and
routing protocol, if the multiple interfaces connect to multiple
access networks which have different measurements of metrics, the
comparing of metrics will be meaningless. However, the current
operating system really does this to choose routing among several
different networks in multiple interfaces situation. For example,
current metric rules define the 100M bps Ethernet network card to be
20 and 10M bps to be 30, but the CDMA data card set its metric value
as 1, although its speed is lower than 100M bps Ethernet network card,
and the host will choose the CDMA data card as the default network
card. This problem confuses the selection of routing in multiple
interfaces situation.

- Hui Min

2009/3/18 Min Hui <[email-masked]>:
> Hi, all mif fans
>
> I have viewed the agenda of mif bof, and I notice some problem
> statements for mif are not concluded in the current ps documents which
> will be discussed in the meeting.
> So I post these additional problems in the mail list for discussion,
> all of them come from the draft
> "draft-hui-ip-multiple-connections-ps-02" with some modifications
> according to the comments received recently.
> There are five problems in addition, which will be proposed in five
> separated mails in order to have sufficient discussion for each of
> them.
> Five mails will be sent out following this mail, the structure is:
> 1. Host routing
> 2. DNS selection
> 3. Different metric measurements
> 4. Source address selection for IPv4
> 5. TOS consideration
>
> Any comment is welcomed, and thanks for your notice.
>
> BR,
> - Hui Min
>

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From: Lars Eggert <[email-masked]>
Date: Tue, 17 Mar 2009 21:20:07 -0700

Hi,

> gateway turns to be the default interface.

RFC1122 Section 3.3.4.3 only talks very broefly about using  
"preference" as a tie breaker and doesn't talk about metrics. Did you  
mean to point to a different RFC?

> card. This problem confuses the selection of routing in multiple

See above - I don't think what you describe is actually defined in  
RFC1122 (or at least, I can't find it there). Is this something that  
we have an RFC about, or is this something you have observed in some  
stack implementations?

Thanks,
Lars

> _______________________________________________
> mif mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/mif

---

From: Min Hui <[email-masked]>
Date: Wed, 18 Mar 2009 18:37:33 +0800

Hi, Lars

Please see my inline reply, thanks.

-Hui Min

2009/3/18 Lars Eggert <[email-masked]>:
> RFC1122 Section 3.3.4.3 only talks very broefly about using "preference" as
> a tie breaker and doesn't talk about metrics. Did you mean to point to a
> different RFC?

It's true RFC1122 only points out the preference. It is the
implementation level solution that the default gateway is chosen
according to metrics which is a form of preference , it can be
observed in Windows operating system.

> See above - I don't think what you describe is actually defined in RFC1122
> (or at least, I can't find it there). Is this something that we have an RFC
> about, or is this something you have observed in some stack implementations?

It's not be defined in any RFC, it is implementation related and can
be observed in Windows operating system, and the reference technical
document can be found in Microsoft web site
http://technet.microsoft.com/en-us/library/bb878104.aspx.
In addition, Linux has different implementation of metrics with
Window, for the same network card will appear different metrics in
these two operating systems.