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Re: What is the most standard subnet length on internet


From: Brett Frankenberger <rbf+nanog () panix com>
Date: Wed, 24 Dec 2008 13:02:17 -0600

On Tue, Dec 23, 2008 at 08:25:40AM -0600, Alex H. Ryu wrote:
Also one of the reason why not putting default route may be because of
recursive lookup from routing table.
If you have multi-homed site within your network with static route, and
if you use next-hop IP address instead of named interface, you will see
the problem when you have default route in routing table.
For an example, if you have "ip route 1.0.0.0 255.0.0.0 2.2.2.2".
If the interface for 2.2.2.2 is down, 1.0.0.0/8 will be still be in the
routing table because 2.2.2.2 can be reached via default route
(0.0.0.0/0) from routing table recursive lookup.
Therefore the traffic for 1.0.0.0/8 will be forwarded to "0.0.0.0/0"
next-hop ip address, and customer fail-over scenario will not be working
at all.

Only way to resolve this problem is... Actually three...
1) Use named interface such as "serial 1/0" instead of "x.x.x.x" IP
next-hop address.
But sometimes this is not an option if you use ethernet circuit or
something like Broadcast or NBMA network.

ip route 1.0.0.0 255.0.0.0 fa0/0 2.2.2.2

     -- Brett


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