ITEM: BD4331L

Why does this IP route add to the wrong interface?

Question:

And what do they mean, all IP interfaces in a machine
must use the same netmask?

I have seen problems when a machine has two interfaces
of this sort:

IP Address      Netmask          Interface
9.1.1.1         255.0.0.0        en0
9.19.169.7      255.255.255.0    tr0

Say you add a route, to reach network 9.19.128, go to
9.19.169.202.  And this route adds perfectly, like so:

9.19.128    9.19.169.202   UG   0   0   en0

Perfectly, except "Why is it on interface en0?  That is
not where I want it routed!"

For some reason, inetd adds the route and thinks it matches
network 9.  Perhaps en0 was the first interface configured
on this machine, but I am not sure.  Definitely, inetd is
having trouble seeing network 9 as different from network
9.19.169.  The remedy is one of the following configurations:

IP Address      Netmask          Interface
10.1.1.1        255.0.0.0        en0
9.19.169.7      255.255.255.0    tr0

IP Address      Netmask          Interface
9.1.1.1         255.255.255.0    en0
9.19.169.7      255.255.255.0    tr0

In the first solution, clearly network 10 is different
from network 9.19.169.  In the second solution, clearly
network 9.1.1 is different from network 9.19.169.




Support Line: Why does this IP route add to the wrong interface? ITEM: BD4331L

Dated: January 1996 Category: N/A

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