________________________________
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.
