Removing DAD in IPv6

Removing DAD in IPv6

[Xia Yang]

Hi all,

I am new to this list, so please forgive me if I say anything
inappropriate.

I am working on a mobility testbed based on IPv6. In order to improve
the performance, I would like to remove the DAD process during the
auto-configuration process of an IPv6 address for my testbed. 

During my experiment, I observed that when an address is configured
based on a router advertisement, the outgoing packets can be sent out
immediately. But the packets destined to local node can only be received
after some time (about 1 sec). I found the lost packets are discarded in
the kernel and never make it to the transport layer. I suspect it is
caused by the DAD process.

I would like to ask for help on how to remove or disable the DAD process
properly, as long as the node can send, receive and forward packets
immediately after a new IPv6 address is generated. Any pointer is
appreciated. Thanks a lot in advance!

Best Regards,

Xia Yang

Re: Removing DAD in IPv6

[YOSHIFUJI Hideaki / 吉藤英明]

In article <1191210807.25398.18.camel@orbit6> (at Mon, 01 Oct 2007 11:53:27 +0800), Xia Yang <xiayang@ntu.edu.sg> says:

> I would like to ask for help on how to remove or disable the DAD process
> properly, as long as the node can send, receive and forward packets
> immediately after a new IPv6 address is generated. Any pointer is
> appreciated. Thanks a lot in advance!

IFA_F_NODAD address flag might help this.

--yoshfuji

Re: Removing DAD in IPv6

[Xia Yang]

Hi,

I just find out this IFA_F_NODAD was not in the kernel used in my test
bed which is 2.6.17. So I tried to modify the code in ipv6/addrconf.c by
myself to remove the DAD:

			if (!max_addresses ||
			    ipv6_count_addresses(in6_dev) < max_addresses)
				ifp = ipv6_add_addr(in6_dev, &addr, pinfo->prefix_len,
						    addr_type&IPV6_ADDR_SCOPE_MASK, 0);

			if (!ifp || IS_ERR(ifp)) {
			    in6_dev_put(in6_dev);
			    return;
			}
// --------New code ----------------
			if (!IS_ERR(ifp)) {
			    spin_lock_bh(&ifp->lock);
			    ifp->flags &= ~IFA_F_TENTATIVE;
			    spin_unlock_bh(&ifp->lock);
			
			    addrconf_join_solict(ifp->idev->dev, &ifp->addr);
			    ipv6_ifa_notify(RTM_NEWADDR, ifp);
			    //in6_ifa_put(ifp);
			    printk("New address configured.\n");
			}
// ----------end -------------------
			update_lft = create = 1;
			ifp->cstamp = jiffies;

			// addrconf_dad_start(ifp, RTF_ADDRCONF|RTF_PREFIX_RT);

However, even the new address is generated and assigned to the
interface, and I can read the address from the /proc interface, my first
few packets are eaten by the kernel. Only until after about 1 second,
then my packet can make its way out. Is kernel doing anything that
blocks the sending and receiving of packets during the time of DAD?
Thanks a lot!

Best Regards,

Xia Yang



On Mon, 2007-10-01 at 20:44 +0900, YOSHIFUJI Hideaki / 吉藤英明 wrote:
> In article <1191210807.25398.18.camel@orbit6> (at Mon, 01 Oct 2007 11:53:27 +0800), Xia Yang <xiayang@ntu.edu.sg> says:
> 
> > I would like to ask for help on how to remove or disable the DAD process
> > properly, as long as the node can send, receive and forward packets
> > immediately after a new IPv6 address is generated. Any pointer is
> > appreciated. Thanks a lot in advance!
> 
> IFA_F_NODAD address flag might help this.
> 
> --yoshfuji