[Ns-bugs] [Bug 188] global routing does not handle ip aliasing

[bugzilla-daemon@nsnam-www.ece.gatech.edu]

http://www.nsnam.org/bugzilla/show_bug.cgi?id=188





------- Comment #5 from craigdo at ee.washington.edu  2008-06-10 11:32 -------
The test case uses the Ipv4AddressHelper to try and create two virtual
networks on a csma channel.  There are three nodes and it tries to assign
two interfaces with different network/address combinations to the first
node/device.  The second node is supposed to get an interface on a
network/address corresponding to one of the first node's (virtual) networks,
and the third node gets a network/address on the other.

What happens here is that the first set of IP address assignments using
Ipv4AddressHelper::Assign() on a collection of two net devices works as
expected.  The second assignment is expected to add a second interface to
the first node, but the helper uses FindInterfaceForDevice to determine if
there already exists an interface talking to the device.  There is an
existing interface in this case, so a new one is not created and the helper
simply changes/overwrites the old IP address with the new one.  

The end result is a network with two nodes on one network number and one
node on another.

The next problem is that the global router code is run.  All of the router
LSAs are exported correctly (but recall the first node only has one
interface, not two).  In the router code, it needs to elect a designated
router for a broadcast network segment.  It does this by walking the channel
and looking for the lowest numbered IP address on the channel.  This, in
turn is done by getting each device from the channel, then doing a
FindIfIndexForDevice() and then a GetAddress().  Yes, since the concept of
one interface per device is implicitly assumed here, the designated router
for network segment 10.1.2.0 is 10.1.1.0 which doesn't make a whole lot of
sense ;-)

Eventually when we're calculating the shortest paths, the confusion comes
back to bite us and when we try to make sense of a nonsensical router ID/IP
address combination the router asserts (it's not a crash,
GetIfIndexByAddress eventually asserts, which is the subject of yet another
bug).

Discussion regarding how to resolve, requirements for new feature, etc.,
required


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