Re: nft chain route hook prerouting / postrouting

[Pablo Neira Ayuso <pablo@netfilter.org>]

Hi,

On Thu, Jun 16, 2016 at 10:44:10AM +0200, Dan Rimal wrote:
> Hello,
> 
> I am trying to rewrite some our firewalls from iptables to nft and i am
> stucked on some iptables features.
> 
> We have two uplinks from different ISP, so we have 2 different public IP
> adresses and LAN with NAT configuration.
> 
> Now, we mark packets on input to distinguish where packet come from to
> our servers, and use this mark on "ip rule" to select appropriate
> routing table, when packet goes back to internet. First routing table
> have default route via ISP1, second routing table have default via ISP2,
> because we can not send SRC IP1 via ISP2 and vice versa (uRPF).
> 
> Iptables do desired marking in this way:
> 
> ## mark packet on input
> iptables -t mangle -A PREROUTING -i $INET_IFACE -j MARK --set-mark 100
> iptables -t mangle -A PREROUTING -i $INET2_IFACE -j MARK --set-mark 101
> 
> ## save mark to conntrack when packet goes to LAN
> iptables -t mangle -A POSTROUTING -j CONNMARK --save-mark
> ## restore mark to response when packet goes to the internet
> iptables -t mangle -A PREROUTING -j CONNMARK --restore-mark
> 
> 
> On some routers, we even mark packet with mask, to preserve some qos
> information saved on mark by TC, for example:
> 
> 
> iptables -t mangle -A PREROUTING -i $INET_IFACE -j MARK --set-mark 201/0xff
> 
> iptables -t mangle -A PREROUTING -j CONNMARK --restore-mark --mask 0xff
> 
> 
> Is there any way, how to implement this behaviour in nftables? I tryied
> to create chain type route hook prerouting/postrouting, but i have got:
> 
> ./fw-base.nft:39:1-73: Error: Could not process rule: Operation not
> supported
> add chain ip route prerouting { type route hook prerouting priority 0; }
>
> I tryied other hook and looks like only output hook is available for
> now. Is it not implemented yet?

Please, use a plain filter chain type instead, eg.

        add chain ip route prerouting { type filter hook prerouting priority 0; }
                                             ^^^^^^

The iptables mangle table only triggers the reroute semantics in the
output chain, ie. in other chains, mangle chains are behaving just
like filter chains.