Re: help programming NAT

From: Tauno Voipio (tauno.voipio_at_iki.fi.NOSPAM.invalid)
Date: 09/09/05

  • Next message: Damir Galič: "help with routing" 
    Date: Fri, 09 Sep 2005 21:08:45 GMT

    Giacomo wrote:
    > Good morning.
    > I'm writing a nat module for study purposes in linux kernel.
    >
    > I do NAT, changing addresses and port in network packets (outgoing and
    > coming back)
    > Then i recalculate checksum.
    >
    > i don't mangle payload (not interested in ftp).
    >
    > Should i do any other adjustment? (TCP window, seq/ack) ?
    >
    > I think it should be enough, since process should be transparent to hosts
    > behind nat machine,
    > the fact is that in some networks it works fine, in other networks
    > communication fails.
    >
    > Tried changing mtu and clamp-tcpmss-to-pmtu with no effect.

    Did you remember to change both the IP checksum and the TCP
    header checksum?

    Get Ethereal and have a look at the mangled packets. It
    will tell you which part is not right. 

    -- 
Tauno Voipio
tauno voipio (at) iki fi
  • Next message: Damir Galič: "help with routing"

    Relevant Pages

    • Re: help programming NAT
      ... > I'm writing a nat module for study purposes in linux kernel. ... No, you should not, the TCP/UDP checksum is the only thing you have to ... change if you change source/destination port. ... > the fact is that in some networks it works fine, ...
      (comp.os.linux.networking)
    • Re: help programming NAT
      ... tcpdump / ethereal tell checksum is always true. ... tcp segment loss appears also when disabling my module and using ... >> I'm writing a nat module for study purposes in linux kernel. ... >> the fact is that in some networks it works fine, ...
      (comp.os.linux.networking)
    • Re: Linksys WRT54G and Firewall software
      ... but, if you take your laptop to other networks it ... The NAT does block incoming connections. ... The XP SP2 firewall does block all incoming connections when configured with no exceptions. ... That does not explain why the computer would need another firewall from the XP SP2 FW when it is connected to other networks. ...
      (comp.security.firewalls)
    • Re: NAT router info please
      ... IP masquerading ... used subset of NAT nowadays. ... communication between networks. ...
      (comp.security.firewalls)
    • Re: newbie to home network dhcp worries
      ... >> networks you are fine. ... you MUST run NAT on at least the Modem(the ... your setup is not much ... >> and IP from the ADSL unit, and the computers get an IP from the BEFSR. ...
      (microsoft.public.win2000.networking)