JOHN@heap.cisco.com (John Wright) (12/01/90)
Over the past few weeks a handful of people have run into an undocumented side effect of the way IP UNNUMBERED works on serial interfaces. The documentation will point this out in the future, we are sending this now to this list to save sites trying to use this the time/grief of discovering this on their own. Interface ether 0 ip address 131.108.4.1 255.255.255.0 ip broadcast 131.108.4.255 Interface serial 0 ip unnumbered ether0 --------remote side examples remote class C remote on same Class B Interface ether 0 Interface ether 0 ip address 192.31.7.27 255.255.255.240 ip address 131.108.5.1 255.255.255.0 ip broadcast 192.31.7.31 ip broadcast 131.108.5.255 Interface serial 0 Interface serial 0 ip unnumbered ether0 ip unnumbered ether0 The above will NOT work, the broadcast addresses associated with the serial interface (those of the tied ethernets) MUST match. In the class C example the broadcast on both sides would need to be 255.255.255.255, in the class B example 131.108.255.255 on both sides would work. The default broadcast is 255.255.255.255 on cisco interfaces without specific ip broadcasts configured. John Wright Customer Engineering cisco Systems, Inc. -------