HP TMS zl Module Security Administrator's Guide

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Configuring a VPN on the HP TMS zl Module
GRE Tunnels
13. To enable the keepalive feature for the GRE tunnel, select Tunnel Keepal-
ive.
a. For Period, type the interval, in seconds, between sending keepalives.
This interval can be a short as 1 second or as long as 3600 seconds (1
hour).
b. For Retry, type the number of keepalives for which the TMS zl Module
can fail to receive a reply before it declares the tunnel to be “down”
(1-255).
Figure 4-246. Manage GRE Wizard > Configure GRE Tunnel Parameters Window
Note The TMS zl Module’s GRE functionality may not properly detect GRE keepal-
ives if a non-TMS endpoint specifies GRE options such as a Checksum or
Sequencing. Normal GRE traffic can be received with these options present,
but GRE keepalives with these options are not handled properly. This results
in the GRE tunnel being detected as down by the non-TMS endpoint of
the GRE tunnel. Please note that the TMS zl Module does not currently include
GRE options such as these, so they cannot be configured for transmission
of GRE traffic from the TMS zl Module.