________________________________
From: Linda Dunbar [mailto:ldunbar at huawei.com]
Sent: Wednesday, September 23, 2009 10:10 AM
To: Shahram Davari; rtg-bfd at ietf.org; dkatz at juniper.net; dward at cisco.com
Subject: RE: How to enforce BFD to be sent over different paths
between two
systems?
Hi Shahram,
Thank you very much for the answers.
Maybe some wording can be improved. For example, if the text says
“transmitting BFD” over multiple paths, it is better to define
what “path”
means. To many people, especially people with transport network
background,
paths mean physical paths. Different LDP or LSP paths between two
systems
may not traverse all the paths between two systems.
I understand that the intent of BFD is to let BFD run over
various media.
But the description of the protocol is under the assumption that
BFD is
running over a path which source can control, like LSP or LDP.
For IP
forwarding, the source can’t control which path to traverse from
A to B. It
is up to intermediate nodes to choose a path.
Linda Dunbar
________________________________
From: Shahram Davari [mailto:davari at broadcom.com]
Sent: Wednesday, September 23, 2009 11:53 AM
To: Linda Dunbar; rtg-bfd at ietf.org; dkatz at juniper.com; dward at cisco.com
Subject: RE: How to enforce BFD to be sent over different paths
between two
systems?
Hi Linda,
I am sure Dave will answer these questions better that I do, but
let me give
you my 2c inline.
Regards,
Shahram
________________________________
From: rtg-bfd-bounces at ietf.org [mailto:rtg-bfd-bounces at ietf.org]
On Behalf
Of Linda Dunbar
Sent: Wednesday, September 23, 2009 9:35 AM
To: rtg-bfd at ietf.org; dkatz at juniper.com; dward at cisco.com
Subject: How to enforce BFD to be sent over different paths
between two
systems?
Dave,
I have some questions on “draft-ietf-bfd-base-09.txt”. Hope you
can help.
1. Section 3: 3rd line of the first paragraph states “A pair
of systems
transmit BFD packets periodically over each path between the two
systems”.
Question: when there are multiple paths between two systems, do
you mean to
have multiple BFD sessions between those two systems, with each
session
covering individual path? How to enforce each path being traversed?
SD> For example there can be multiple LSPs between two systems
and you need
to run BFD separately on each LSP.
2. The Echo function is pretty much like “Ping”. Each system
can
initiate a “Ping” to another system. Is “periodic Ping” an accurate
description of the “Echo function”?
SD> Your understanding is correct. But note that Echo packets are
not BFD
packets. BFD just negotiates the Echo interval.
3. Section 4.1 under the “Control Plane Independent” sub-
section:
The first paragraph states “if clear, the transmitting system’s BFD
implementation share fate with its control plane”.
Question: When the transmitting system is running multiple routing
protocols, more than one signaling schemes for different
services, is it
necessary to indicate which routing protocol and which signaling
protocol?
Actually, BFD is to test connectivity which can be up when the
corresponding control plane is done. What is the reason to have
BFD share
fate with its transmitting system’s control plane?
SD> Every LSP or PW or tunnel that runs BFD could be setup using
an instance
of control plane. We don't care about the control plane of the
client or
server layers. What this bit indicates is the control-plane for
the layer
you are running the BFD on.
4. The BFD’s Control Packet Format described in Section 4.1
has a bit
field for Demand mode. Why not having a bit field for the other
two modes
(Async and Echo)?
SD> If D=0 it means Async mode. For Echo, if a system does not
want to
receive Echo it can set "Required Min Echo RX Interval " = 0 .
And there is
not need to signal that you want to Tx Echo.
5. Is the Discriminator field of the BFD’ Control Packet
Format same as
unique identifier for particular BFD session from one system? Why
not call
it Identifier? Is it negotiated between the two systems?
SD> the Discr is a locally unique number (not globally) very
similar to
an LSP MPLS label that is distributed from a downstream node. It
it not
negotiated.
6. Section 6.18.17 Concatenated Paths
In transport network, Concatenated paths mean to combine (or
bundle)
multiple paths to form a bigger path which has higher bandwidth.
Therefore,
failure on one of the paths concatenated together will not cause
connectivity problem for the two systems exchanging BFD. This
failure will
only cause the bandwidth of the concatenated path to be smaller.
Do you mean
that when one of the paths within a concatenated path fail, the
BFD should
indicate this partial failure of the concatenated path?
SD> As far as I know concatenated paths in transport networks
mean stitching
two connections such as two LSPs.
7. Editorial: Section 2 Design: 6th line of the first
paragraph:
“making it useful in concert with”? Is it a typo?
Thank you very much for helping me.
Best Regards, Linda Dunbar
Advanced Technology Dept, Wireline Networks,
Huawei Technologies, Inc.
