答复: [PATCH] net: Fix the arp error in some cases

["Guodeqing (A)" <geffrey.guo@huawei.com>]

-----邮件原件-----
发件人: David Ahern [mailto:dsahern@gmail.com] 
发送时间: Saturday, June 13, 2020 22:32
收件人: Guodeqing (A) <geffrey.guo@huawei.com>; davem@davemloft.net
抄送: kuznet@ms2.inr.ac.ru; netdev@vger.kernel.org; dsa@cumulusnetworks.com; kuba@kernel.org
主题: Re: [PATCH] net: Fix the arp error in some cases

On 6/13/20 12:49 AM, guodeqing wrote:
> ie.,
> $ ifconfig eth0 6.6.6.6 netmask 255.255.255.0
> 
> $ ip rule add from 6.6.6.6 table 6666

without a default entry in table 6666 the lookup proceeds to the next table - which by default is the main table. 

---yes，if without the rule，this problem will not happen. 
  Follow the steps:
  $ ifconfig eth0 6.6.6.6 netmask 255.255.255.0
  $ ip route add 9.9.9.9 via 6.6.6.6
  $ ping -I 6.6.6.6 9.9.9.9
  And The arp request address is 9.9.9.9 and is right.(" gateway can be actually local interface address,
 *    so that gatewayed route is direct")

> 
> $ ip route add 9.9.9.9 via 6.6.6.6
> 
> $ ping -I 6.6.6.6 9.9.9.9
> PING 9.9.9.9 (9.9.9.9) from 6.6.6.6 : 56(84) bytes of data.
> 
> ^C
> --- 9.9.9.9 ping statistics ---
> 3 packets transmitted, 0 received, 100% packet loss, time 2079ms
> 
> $ arp
> Address     HWtype  HWaddress           Flags Mask            Iface
> 6.6.6.6             (incomplete)                              eth0
> 
> The arp request address is error, this problem can be reproduced easily.
> 
> Fixes: 3bfd847203c6("net: Use passed in table for nexthop lookups")
> Signed-off-by: guodeqing <geffrey.guo@huawei.com>
> ---
>  net/ipv4/fib_semantics.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c index 
> e53871e..1f75dc6 100644
> --- a/net/ipv4/fib_semantics.c
> +++ b/net/ipv4/fib_semantics.c
> @@ -1109,7 +1109,7 @@ static int fib_check_nh_v4_gw(struct net *net, struct fib_nh *nh, u32 table,
>  		if (fl4.flowi4_scope < RT_SCOPE_LINK)
>  			fl4.flowi4_scope = RT_SCOPE_LINK;
>  
> -		if (table)
> +		if (table && table != RT_TABLE_MAIN)
>  			tbl = fib_get_table(net, table);
>  
>  		if (tbl)
> 

how does gateway validation when the route is installed affect arp resolution?

you are missing something in explaining the problem you are seeing.

-- This problem can only happen in some cases,this 3bfd847203c6 patch will do the main table lookup error in some cases, and I think it should not do the main table lookup because the next function fib_lookup does the maintable lookup.