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Hi
Linda,
That
is correct. For IP there is only one path (shortest path) between two
systems.
Regards,
Shahram 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] 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 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 “ 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. |