3Com 4007, Implementation Manual, Page: 442 / 684

442 C
HAPTER
18: IP M
ULTICAST
R
OUTING
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You must define the tunnel on both end points — that is, on both the
local module and the remote system — even though you specify the
address of the remote router interface in the local module.
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DVMRP interfaces and tunnels have similar characteristics (metric and
TTL threshold), but the tunnel characteristics do not have to match the
interface characteristics.
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If you try to remove an IP interface, and you have a tunnel defined on
that interface, the module warns you with an error message. You
must remove the tunnel before you can remove the IP interface.
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You can define multiple multicast tunnel end points on the same local
routing interface, but each must lead to different remote end points.
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When you define a tunnel, the module assigns a tunnel index number
to it. The multicast tunnel display lists tunnels in ascending order by
the tunnel index number. Tunnel index numbers provide a way to
identify and remove individual tunnels, which is especially useful when
multiple tunnel end points are configured on the same routing
interface.
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When you remove a tunnel, the module does not dynamically reorder
remaining tunnels in the multicast tunnel display. For example, if you
had three tunnels with tunnel index numbers 1, 2, and 3 and you then
removed tunnel 2, the multicast tunnel display lists the remaining
tunnels and identifies them with their original tunnel index numbers
(1 and 3). The module does not dynamically reassign tunnel index
numbers (does not change 3 to 2). In this example, the module
assigns tunnel index 2 to the next
new tunnel that you define. After
the modules uses index 2, it can assign index 4 to the next new
tunnel, and so on.
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Removing a tunnel end point on one system destroys that tunnel’s
functionality, but 3Com recommends that you remove the tunnel
configuration from both systems.