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Dave and David, Forgive me for not aware of the
history of the BFD development. Reading through the “BFD for IPv4 and
IPv6 (Single Hop)” (draft-ietf-bfd-v4v6-1hop-10.txt), I am not clear why
single hop BFD is needed, especially for two immediately connected neighbors.
There is Hello message between two immediate neighbors. If two immediate
neighbors need logical layer to detect any failure between the two immediate
neighbors, they can use the Hello message to achieve this purpose. Even though
Hello message is from control Plane, it would be much less work for
routers/LSRs to monitor the Hello messages than creating a new BFD session. Any physical media, like 802.3,
SONET, DWDM wavelength all have physical failure indication. Each neighbor can
also use the physical failure indication to declare the connectivity between
two immediate neighbors, which is much faster than a BFD session, isn’t
it? It also needs less processing on the router/LSR, there won’t be any
proactive periodical sending BFD over the link anymore. Can you explain (or add to the
document) what is the reason for having single hop BFD? Is single Hop BFD only for the Tunnel scenario? In Section 2 (Application and Limitation), the last
paragraph does indicate that the transmitted packets are immediately routed
back towards the sender on the interface over which they where sent if BFD Echo
function is used. But when Link Aggregation is used to bundle the multiple
parallel links between two neighbors, how does the network layer enforce which
link to send back the “echo” message? Even if BFD ECHO can be enforced to be sent back on the same
interface port so that the individual link’s failure can be detected,
what can this fault do when this fault can’t affect the connectivity
between the two immediate neighbors in control plane’s view? All
the links are bundled and two immediate neighbors are still connected? Thank you very much, Linda Dunbar Advanced Technology Dept, Wireline
Networks, Huawei Technologies, Inc. |