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Re: DNAT + ADSL... to reduce MTU of the network

ronan lopes wrote:
I am having problems to use DNAT in one gateway with external interface ppp0 and internal interface eth1 Already I placed MTU low 890 of eth0 very; but ppp0 only connects with MTU 1492 would like to reduce this MTU, therefore when I use the rule:
iptables -A FORWARD -p tcp -m tcp --tcp-flags \
SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu


iptables -t nat -I PREROUTING -p tcp --dport 3389 \
-j DNAT --to

    it does not function!
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I think, if I remember you don't need to touch the MTU of eth0... only ppp0 need to be set to 1492 or less if using any type of VPN...

I also think, if I remember that you don't need the iptables rule with clamp-mss-to-pmtu if you change the MTU manually !

For the DNAT, after the DNAT rule, you need to allow the traffic in the table "filter" with a rule like that:
iptables -t filter -A FORWARD -m state --state NEW \
-i <external interface> -o eth1 -d --dport 3389 -j ACCEPT

I'm sure about this point.... after a DNAT, you MUST allow the traffic in table "filter"


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