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

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Message-ID: <55929b71c9b24aeeba760585fc59497f@huawei.com>
Date:   Wed, 17 Jun 2020 03:38:11 +0000
From:   "Guodeqing (A)" <geffrey.guo@...wei.com>
To:     David Ahern <dsahern@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     "kuznet@....inr.ac.ru" <kuznet@....inr.ac.ru>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "dsa@...ulusnetworks.com" <dsa@...ulusnetworks.com>,
        "kuba@...nel.org" <kuba@...nel.org>
Subject: 答复: [PATCH] net: Fix the arp error in some cases

rt_set_nexthop in __mkroute_output will check the nh->nh_scope value to determine whether to use the gw or not.
		if (nh->nh_gw && nh->nh_scope == RT_SCOPE_LINK) {
			rt->rt_gateway = nh->nh_gw;
			rt->rt_uses_gateway = 1;
		}

(ip_route_output_key_hash-> ip_route_output_key_hash_rcu-> __mkroute_output-> rt_set_nexthop)

-----邮件原件-----
发件人: David Ahern [mailto:dsahern@...il.com] 
发送时间: Wednesday, June 17, 2020 11:10
收件人: Guodeqing (A) <geffrey.guo@...wei.com>; davem@...emloft.net
抄送: kuznet@....inr.ac.ru; netdev@...r.kernel.org; dsa@...ulusnetworks.com; kuba@...nel.org
主题: Re: [PATCH] net: Fix the arp error in some cases

On 6/16/20 8:07 PM, guodeqing wrote:
> ie.,
> $ ifconfig eth0 6.6.6.6 netmask 255.255.255.0
> 
> $ ip rule add from 6.6.6.6 table 6666
> 
> $ 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.
> 
> 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 is because fib_table_lookup in 
> fib_check_nh lookup the destnation 9.9.9.9 nexthop, the scope of the 
> fib result is RT_SCOPE_LINK,the correct scope is RT_SCOPE_HOST.
> Here I add a check of whether this is RT_TABLE_MAIN to solve this problem.

fib_check_nh* is only used when the route is installed into the FIB to verify the gateway is legit. It is not used when processing arp requests. Why then, do you believe this fixes something?