netdev - Re: [PATCH] net: Fix the arp error in some cases

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Date:   Sat, 13 Jun 2020 08:31:54 -0600
From:   David Ahern <dsahern@...il.com>
To:     guodeqing <geffrey.guo@...wei.com>, davem@...emloft.net
Cc:     kuznet@....inr.ac.ru, netdev@...r.kernel.org,
        dsa@...ulusnetworks.com, kuba@...nel.org
Subject: 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.

> 
> $ 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@...wei.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.