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@ni.com Cc: Joe Hershberger joe.hershberger@gmail.com --- Changes for v2: - Guard with #ifdef CONFIG_CMD_LINK_LOCAL Changes for v3: - Rebased onto other changed patches
net/arp.c | 14 ++++++++++++++ 1 files changed, 14 insertions(+), 0 deletions(-)
diff --git a/net/arp.c b/net/arp.c index 908ebf5..0b0ccbb 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 NetSendPacket((uchar *)et, eth_hdr_size + ARP_HDR_SIZE); return;