linux-kernel - Re: [PATCH net v2] net: vrf: Fix ping failed when vrf mtu is set to 0

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Message-ID: <18b082d4-cef9-bb39-0680-8187f6951bbc@cumulusnetworks.com>
Date:   Sun, 7 Apr 2019 07:30:29 -0700
From:   David Ahern <dsa@...ulusnetworks.com>
To:     linmiaohe <linmiaohe@...wei.com>,
        Shrijeet Mukherjee <shrijeet@...il.com>, davem@...emloft.net,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Mingfangsen <mingfangsen@...wei.com>
Subject: Re: [PATCH net v2] net: vrf: Fix ping failed when vrf mtu is set to 0

On 4/6/19 11:46 PM, linmiaohe wrote:
> diff --git a/drivers/net/vrf.c b/drivers/net/vrf.c
> index 7c1430ed0244..4d35d37f225a 100644
> --- a/drivers/net/vrf.c
> +++ b/drivers/net/vrf.c
> @@ -43,6 +43,12 @@
> 
>  #define FIB_RULE_PREF  1000       /* default preference for FIB rules */
> 
> +/* The MTU is really irrelevant for VRF except for odd cases, so limit it
> + * to a reasonable range which both works for IPV4 and IPV6.
> + */
> +#define VRF_MIN_MTU	1280      /* same as IPV6_MIN_MTU */
> +#define VRF_MAX_MTU	0xFFFFU   /* same as IP_MAX_MTU */

Since VRF does not care about MTU, there is no reason for VRF specific
macros.

> +
>  static unsigned int vrf_net_id;
> 
>  struct net_vrf {
> @@ -1274,8 +1280,8 @@ static void vrf_setup(struct net_device *dev)
>  	/* default to no qdisc; user can add if desired */
>  	dev->priv_flags |= IFF_NO_QUEUE;
> 
> -	dev->min_mtu = 0;
> -	dev->max_mtu = 0;
> +	dev->min_mtu = VRF_MIN_MTU;
> +	dev->max_mtu = VRF_MAX_MTU;

Set these to IPV6_MIN_MTU and ETH_MAX_MTU and add a comment that VRF
devices do not care about MTU, but if the MTU is set too low then the
ipv4 and ipv6 protocols are disabled which breaks networking.