netdev - Re: [PATCHv4 net-next] vxlan: virtual extensible lan

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Message-ID: <CAEP_g=_PQSx_OVcU47OJFKgO_MpWSKStmGnVB76vSm=Z7r6mvg@mail.gmail.com>
Date:	Tue, 25 Sep 2012 14:55:13 -0700
From:	Jesse Gross <jesse@...ira.com>
To:	Stephen Hemminger <shemminger@...tta.com>
Cc:	Chris Wright <chrisw@...hat.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCHv4 net-next] vxlan: virtual extensible lan

On Mon, Sep 24, 2012 at 2:50 PM, Stephen Hemminger
<shemminger@...tta.com> wrote:
> +static netdev_tx_t vxlan_xmit(struct sk_buff *skb, struct net_device *dev)
[...]
> +       /* Do PMTU */
> +       if (skb->protocol == htons(ETH_P_IP)) {
> +               df |= old_iph->frag_off & htons(IP_DF);
> +               if (df && mtu < pkt_len) {
> +                       icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
> +                                 htonl(mtu));
> +                       ip_rt_put(rt);
> +                       goto tx_error;
> +               }
> +       }
> +#if IS_ENABLED(CONFIG_IPV6)
> +       else if (skb->protocol == htons(ETH_P_IPV6)) {
> +               if (mtu >= IPV6_MIN_MTU && mtu < pkt_len) {
> +                       icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);
> +                       ip_rt_put(rt);
> +                       goto tx_error;
> +               }
> +       }
> +#endif

Won't this black hole packets if we need to generate ICMP messages?
Since we're doing switching and not routing here icmp_send() doesn't
necessarily have a route to the relevant endpoint.  It looks like
Ethernet over GRE has this issue as well.
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