[c-nsp] 3750 CEF and equal cost multihoming

[Matt Bazan]

Have a mystery I'd like to solve:  On one of my 3750 switches I've setup
two static routes with equal metrics (on two separate routed ports) via
their respected interfaces (gi1/0/19, gi1/0/21) to a /27 network.  So,
I've got two routes in my routing table that look like this:

 XX.XXX.XXX.XXX/27 is directly connected, GigabitEthernet1/0/19
                   is directly connected, GigabitEthernet1/0/21

Problem is, when I try to ping one of the machines on this block half of
the pings timeout.  From looking at a sniff of the traffic I'm seeing
that both interfaces will arp for the address in question and when the
reply comes back the router seems to hang for a couple seconds
(corresponding to the ping timeout).  Finally a couple ping requests
will go through.  At some point in this process the arp entry will be
linked to one of the interfaces.  What appears to happen, however, is
that the router, seeing it has two routes for this block and that one of
the ints does not have an arp mapping for this address, will proceed to
arp down the interface that doesnt have the mapping.  This again causes
the router to hang.

In looking at the FIB I see that there are two entries, one for the
interface routes and one for the host address.  Is this causing a
problem?  I know this is not the preferred way of going about this but
I'd like to get this working, if possible.  

Is it possible to have the router only use the interface that has the
arp entry mapped to it?

Thanks for the help.

  Matt