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The way HP-UX 11.23 chooses a route

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Occasional Collector

The way HP-UX 11.23 chooses a route

Dear all,


We have an Itanium machine with HP-UX 11.23.  The routing table is the following:


Destination           Gateway            Flags   Refs Interface  Pmtu
localhost             localhost          UH        0  lo0        4136
L5SVA                 L5SVA              UH        0  lan5       4136
L2SVA                 L2SVA              UH        0  lan2       4136
server1               server1            UH        0  lan0       4136
L1SVA                 L1SVA              UH        0  lan1       4136
L4SVA                 L4SVA              UH        0  lan4       4136
L3SVA                 L3SVA              UH        0  lan3       4136      UGH       0  lan0          0      UGH       0  lan0          0      UGH       0  lan0          0      UGH       0  lan0          0           L1SVA              U         2  lan1       1500           L2SVA              U         2  lan2       1500          L3SVA              U         2  lan3       1500          L4SVA              U         2  lan4       1500          L5SVA              U         2  lan5       1500         server1            U         2  lan0       1500
loopback              localhost          U         0  lo0           0
default             UG        0  lan1          0


But when we traceroute it selects LAN3 somehow? 

server1,sys,root # traceroute
traceroute: Warning: Multiple interfaces found; using @ lan3 traceroute to (, 30 hops max, 40 byte packets
 1  * * *
 2  * * *


Could you help to understand why???



Duncan Edmonstone
Honored Contributor

Re: The way HP-UX 11.23 chooses a route

A "netstat -rn" would be easier to interpret than just "netstat -r"


Honored Contributor

Re: The way HP-UX 11.23 chooses a route

The HP-UX traceroute does not use the routing table at all. If you don't use the one of the options "-i <interface>" or "-s <source-IP>", it simply uses the first network interface it sees.


"man traceroute" says:

Note: On a multi-homed host, if traceroute is invoked without the -s
or -i options, the source address used for the probe packets may not
be the same as the address of the interface through which they are
sent out.  As a result, the destination or the next hop may not be
able to reply to the probe and traceroute(1) may not display the route
to the destination properly.  Thus, in the multi-homed host case, use
the -s or -i options to explicitly specify the appropriate source
address for probes.

 So when you have a multi-homed host (two or more non-APA network interfaces) you should use the -i or -s options with traceroute to make sure it uses the right interface for the trace.