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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. |