netdev - Re: Should linux send netlink message as it is deleting that routing entry?

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Message-ID: <20140411113042.4328c39c@nehalam.linuxnetplumber.net>
Date:	Fri, 11 Apr 2014 11:30:42 -0700
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	zhuyj <zyjzyj2000@...il.com>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	ebiederm@...ssion.com, ja@....bg,
	"Yang, Zhangle (Eric)" <Zhangle.Yang@...driver.com>,
	"Tao, Yue" <Yue.Tao@...driver.com>,
	"Zadoyan, Grant" <Grant.Zadoyan@...driver.com>,
	eric.dumazet@...il.com, socketcan@...tkopp.net,
	hannes@...essinduktion.org, cwang@...pensource.com
Subject: Re: Should linux send netlink message as it is deleting that
 routing entry?

On Fri, 11 Apr 2014 17:15:48 +0800
zhuyj <zyjzyj2000@...il.com> wrote:

> > With ubuntu 12.04, I run the following to reproduce this defect.
> >
> > 1) Configure an interface
> > ifconfig eth1 150.0.0.1/24 up
> >
> > 2) Add routing entry via that interface address
> > route add -net 200.0.0.0/24 gw 150.0.0.1
> >
> > 3) Change the ip address on that interface as shown below.
> > ifconfig eth1 151.0.0.1/24 up
> >
> > 4) Check netlink messages with "ip monitor all". There is no route 
> > delete netlink message.
> >

With IPv4 there are several cases where there is a non-notified
implicit route withdrawal. This is not something that can be fixed.
There are two issues:
 1. with large backbone size route tables (ie 1M routes), the number
    of notification messages becomes a bottleneck and would be unreliable
 2. the existing routing daemons (quagga, bird, etc) all understand/expect
    the existing semantics

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