netdev - Re: VRF Issue Since kernel 5

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Date:   Wed, 11 Sep 2019 11:19:06 +0000
From:   Gowen <gowen@...atocomputing.co.uk>
To:     David Ahern <dsahern@...il.com>, Alexis Bauvin <abauvin@...ine.net>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: VRF Issue Since kernel 5

Hi there,

Your perf command:

  isc-worker0000 20261 [000]  2215.013849: fib:fib_table_lookup: table 10 oif 0 iif 0 proto 0 0.0.0.0/0 -> 127.0.0.1/0 tos 0 scope 0 flags 0 ==> dev eth0 gw 10.24.12.1 src 10.24.12.10 err 0
  isc-worker0000 20261 [000]  2215.013915: fib:fib_table_lookup: table 10 oif 4 iif 1 proto 17 0.0.0.0/52138 -> 127.0.0.53/53 tos 0 scope 0 flags 4 ==> dev eth0 gw 10.24.12.1 src 10.24.12.10 err 0
  isc-worker0000 20261 [000]  2220.014006: fib:fib_table_lookup: table 10 oif 4 iif 1 proto 17 0.0.0.0/52138 -> 127.0.0.53/53 tos 0 scope 0 flags 4 ==> dev eth0 gw 10.24.12.1 src 10.24.12.10 err 0

Also I set all iptables to policy ACCEPT and flushed the rules, enabled forwarding, checked the sysctl settings are all '1'. I've looked at tracing DNS through the iptables and I see that DNS uses a loopback interface as source and destination - this would be odd on a Cisco box but having looked around this appears to be normal?

I also gathered an strace of updating the package cache as well as a perf of the same command - will send if interested (is more verbose and not sure if the spam filter will block it)

Gareth

From: Gowen

Sent: 11 September 2019 06:09

To: David Ahern <dsahern@...il.com>; Alexis Bauvin <abauvin@...ine.net>

Cc: netdev@...r.kernel.org <netdev@...r.kernel.org>

Subject: RE: VRF Issue Since kernel 5

Thanks for the link - that's really useful. I did re-order ip rules Friday (I think) - no change

-----Original Message-----

From: David Ahern <dsahern@...il.com> 

Sent: 10 September 2019 17:36

To: Alexis Bauvin <abauvin@...ine.net>; Gowen <gowen@...atocomputing.co.uk>

Cc: netdev@...r.kernel.org

Subject: Re: VRF Issue Since kernel 5

On 9/9/19 1:01 PM, Alexis Bauvin wrote:

> Could you try swapping the local and l3mdev rules?

> 

> `ip rule del pref 0; ip rule add from all lookup local pref 1001`

yes, the rules should be re-ordered so that local rule is after l3mdev rule (VRF is implemented as policy routing). In general, I would reverse the order of those commands to ensure no breakage.

Also, 5.0 I think it was (too many kernel versions) added a new l3mdev sysctl (raw_l3mdev_accept). Check all 3 of them and nmake sure they are set properly for your use case.

These slides do not cover 5.0 changes but are still the best collection of notes on VRF:

http://schd.ws/hosted_files/ossna2017/fe/vrf-tutorial-oss.pdf