Subject: Re: [PATCH 2/3] IPVS: make friends with nf_conntrack

From: Patrick McHardy <[email-masked]>
Date: Wed, 02 Sep 2009 16:56:08 +0200

Hannes Eder wrote:
> Update the nf_conntrack tuple in reply direction, as we will see
> traffic from the real server (RIP) to the client (CIP).  Once this is
> done we can use netfilters SNAT in POSTROUTING, especially with
> xt_ipvs, to do source NAT, e.g.:
> 
> % iptables -t nat -A POSTROUTING -m ipvs --vaddr 192.168.100.30/32 --vport 8080 \
>> -j SNAT --to-source 192.168.10.10
> 

> +static void
> +ip_vs_update_conntrack(struct sk_buff *skb, struct ip_vs_conn *cp)
> +{
> +	struct nf_conn *ct = (struct nf_conn *)skb->nfct;
> +
> +	if (ct == NULL || ct == &nf_conntrack_untracked ||
> +	    nf_ct_is_confirmed(ct))
> +		return;
> +
> +	/*
> +	 * The connection is not yet in the hashtable, so we update it.
> +	 * CIP->VIP will remain the same, so leave the tuple in
> +	 * IP_CT_DIR_ORIGINAL untouched.  When the reply comes back from the
> +	 * real-server we will see RIP->DIP.
> +	 */
> +	ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.u3 = cp->daddr;
> +	/*
> +	 * This will also take care of UDP and other protocols.
> +	 */
> +	ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.u.tcp.port = cp->dport;
> +}

How does IPVS interact with conntrack helpers? If it does actually
intend to use them (which will happen automatically), it might make
sense to use nf_conntrack_alter_reply(), which will perform a new
helper lookup based on the changed tuple.