netdev - Re: iproute2 - modifying routes in place

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Message-ID: <7b4fac83-210f-2e91-5e56-6a381bd2a5ba@gmail.com>
Date:   Mon, 14 May 2018 12:49:38 -0600
From:   David Ahern <dsahern@...il.com>
To:     Ryan Whelan <rcwhelan@...il.com>
Cc:     netdev@...r.kernel.org
Subject: Re: iproute2 - modifying routes in place

On 5/14/18 12:40 PM, Ryan Whelan wrote:
> Same behavior:
> 
> 
> root@...elan-linux ~
> # ip -6 route
> ::1 dev lo proto kernel metric 256 pref medium
> fd9b:caee:ff93:ceef:3431:3831:3930:3031 dev internal0 proto kernel metric
> 256 pref medium
> fd9b:caee:ff93:ceef:3431:3831:3930:3032 dev internal0 src
> fd9b:caee:ff93:ceef:3431:3831:3930:3031 metric 1024 pref medium
> fe80::/64 dev enp0s3 proto kernel metric 256 pref medium
> fe80::/64 dev enp0s8 proto kernel metric 256 pref medium
> fe80::/64 dev internal0 proto kernel metric 256 pref medium
> 
> root@...elan-linux ~
> # ip -6 route change fd9b:caee:ff93:ceef:3431:3831:3930:3032 dev internal0
> src fd9b:caee:ff93:ceef:3431:3831:3930:3031 metric 10
> RTNETLINK answers: No such file or directory

'change' only sets NLM_F_REPLACE. Since NLM_F_CREATE is not set ('ip ro
replace') it does not add a new route and expects one to exist. Your
table above shows the prefix with metric 256 not metric 10 so the route
does not match. You should be seeing a message in dmesg to this effect.

> 
> root@...elan-linux ~
> # ip -6 route replace fd9b:caee:ff93:ceef:3431:3831:3930:3032 dev internal0
> src fd9b:caee:ff93:ceef:3431:3831:3930:3031 metric 10

Adds a new entry because of NLM_F_CREATE.

> 
> root@...elan-linux ~
> # ip -6 route
> ::1 dev lo proto kernel metric 256 pref medium
> fd9b:caee:ff93:ceef:3431:3831:3930:3031 dev internal0 proto kernel metric
> 256 pref medium
> fd9b:caee:ff93:ceef:3431:3831:3930:3032 dev internal0 src
> fd9b:caee:ff93:ceef:3431:3831:3930:3031 metric 10 pref medium
> fd9b:caee:ff93:ceef:3431:3831:3930:3032 dev internal0 src
> fd9b:caee:ff93:ceef:3431:3831:3930:3031 metric 1024 pref medium
> fe80::/64 dev enp0s3 proto kernel metric 256 pref medium
> fe80::/64 dev enp0s8 proto kernel metric 256 pref medium
> fe80::/64 dev internal0 proto kernel metric 256 pref medium
> 
> root@...elan-linux ~
> # uname -a
> Linux rwhelan-linux 4.17.0-rc3-ipv6-route-bugs+ #2 SMP Mon May 14 11:30:38
> EDT 2018 x86_64 x86_64 x86_64 GNU/Linux
> On Sat, May 12, 2018 at 1:01 PM David Ahern <dsahern@...il.com> wrote:
> 
>> On 5/11/18 4:42 AM, Ryan Whelan wrote:
>>> `ip route` has 2 subcommands that don't seem to work as expected and i'm
>>> not sure if its a bug, or if i'm misunderstanding the semantics.
> 
>> Can you try with ipv6/route-bugs branch in
>> https://github.com/dsahern/linux