[Nfd-dev] Expiration time of the RIB entry at the NDN nodes

Junxiao Shi shijunxiao at email.arizona.edu
Fri Feb 3 18:41:28 PST 2017


Hi Jongdeog

  So I guess if the pingserver is not idle, the prefix at the Illinois node
> would not be expired, right?
>

If the connection between end host and gateway router is good, and there's
no problem with certificate retrieval, the prefix registered on Illinois
node should not disappear, regardless of whether the pingserver is idle or
not.

Routes registered via auto prefix propagation are set to "never expire", so
that they will not appear as long as the face does not appear.
A UDP on-demand face has a default idle timeout of 600 seconds (router's
nfd.conf face_system.udp.idle_timeout key), which means your end host must
send something to the router at least once every 600 seconds. If everything
else is idle, auto prefix propagation can still fulfill this requirement by
sending a prefix registration command once every 300 seconds (end host's
nfd.conf rib.auto_prefix_propagate.refresh_interval key).

However, there are two possible reasons that can cause the face to
disappear.

First, if there is a network connectivity problem that causes either end to
receive an ICMP error, the face disappears on that end.
On end host side, you can prevent this situation by creating the face with
persistency set to permanent. The command is nfdc create -P udp4://
192.0.2.1:6363 for NFD 0.5.1 or below, and nfdc face create udp4://
192.0.2.1:6363 permanent for upcoming NFD version.
In case the face disappears on router side, the next prefix registration
command will create a new face on the router and add the prefix again.

Second, if there is a certificate retrieval problem, or any other reason
that causes the prefix registration command sent by auto prefix propagation
to fail, the exponential back-off retrying algorithm in auto prefix
propagation will kick in. The base retry wait is 50 seconds, and the
maximum retry wait is as long as 3600 seconds (end host's nfd.conf
rib.auto_prefix_propagate section). This means, if prefix registration
command has failed four times, the retry wait would increase to 800 seconds
which is greater than UDP on-demand face's idle timeout, and then you'll
observe the end host's face appear and disappear on the router one time or
another.

But if there's no ICMP error and no error during prefix registration, none
of these would happen.

Yours, Junxiao
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