[U-Boot] [PATCH v2 3/3] net: Work-around for brain-damaged Cisco equipment with arp-proxy

[Simon Glass]

Hi Joe,

On Tue, Mar 27, 2012 at 4:43 PM, Joe Hershberger <joe.hershberger at ni.com> wrote:
> Cisco's arp-proxy feature fails to ignore the link-local address range
> This means that a link-local device on a network with this Cisco
> equipment will reply to ARP requests for our device (in addition to
> our reply).
> If we happen to reply first, the requester's ARP table will be
> populated with our MAC address, and one packet will be sent to us...
> shortly following this, the requester will get an ARP reply from the
> Cisco equipment telling the requester to send packets their way
> instead of to our device from now on.
> This work-around detects this link-local condition and will delay
> replying to the ARP request for 5ms so that the first packet is sent
> to the Cisco equipment and all following packets are sent to our
> device.
>
> Signed-off-by: Joe Hershberger <joe.hershberger at ni.com>
> Cc: Joe Hershberger <joe.hershberger at gmail.com>
> Cc: Simon Glass <sjg at chromium.org>
> Cc: Mike Frysinger <vapier at gentoo.org>
> ---
> Changes for v2:
>   - Guard with #ifdef CONFIG_CMD_LINK_LOCAL
>
>  net/arp.c |   14 ++++++++++++++
>  1 files changed, 14 insertions(+), 0 deletions(-)
>
> diff --git a/net/arp.c b/net/arp.c
> index 7599d30..56c5da8 100644
> --- a/net/arp.c
> +++ b/net/arp.c
> @@ -169,6 +169,20 @@ void ArpReceive(struct Ethernet_hdr *et, struct IP_UDP_hdr *ip, int len)
>                NetCopyIP(&arp->ar_tpa, &arp->ar_spa);
>                memcpy(&arp->ar_sha, NetOurEther, ARP_HLEN);
>                NetCopyIP(&arp->ar_spa, &NetOurIP);
> +
> +#ifdef CONFIG_CMD_LINK_LOCAL
> +               /*
> +                * Work-around for brain-damaged Cisco equipment with
> +                *   arp-proxy enabled.
> +                *
> +                *   If the requesting IP is not on our subnet, wait 5ms to
> +                *   reply to ARP request so that our reply will overwrite
> +                *   the arp-proxy's instead of the other way around.
> +                */
> +               if ((NetReadIP(&arp->ar_tpa) & NetOurSubnetMask) !=
> +                   (NetReadIP(&arp->ar_spa) & NetOurSubnetMask))
> +                       udelay(5000);
> +#endif

I'm sure this solves the problem, but is 5ms enough, and should we
make this a CONFIG option so it can be turned off if needed?

>                NetSendPacket((uchar *)et, eth_hdr_size + ARP_HDR_SIZE);
>                return;
>
> --
> 1.6.0.2
>

Regards,
Simon