[110103] in North American Network Operators' Group
Re: What is the most standard subnet length on internet
daemon@ATHENA.MIT.EDU (Brett Frankenberger)
Wed Dec 24 14:02:52 2008
Date: Wed, 24 Dec 2008 13:02:17 -0600
From: Brett Frankenberger <rbf+nanog@panix.com>
To: "Alex H. Ryu" <r.hyunseog@ieee.org>
In-Reply-To: <4950F4E4.2080401@ieee.org>
Cc: nanog list <nanog@nanog.org>, Grzegorz Janoszka <Grzegorz@Janoszka.pl>
Errors-To: nanog-bounces@nanog.org
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
