Is there anything weird I should know about using ipfw on alias
smithi at nimnet.asn.au
Wed Dec 3 07:57:23 PST 2008
On Tue, 2 Dec 2008, Brett Davidson wrote:
> Ian Smith wrote:
> > On Mon, 01 Dec 2008 16:52:12 +1300 Brett Davidson <brett at net24.co.nz>
> > wrote:
> > > ifconfig shows the alias addresses correctly bound.
> > > Creating an ipfw rule and testing it from the command line works >
> > (connects out from master address, not alias)
> > > > From website on alias address, the firewall blocks the packets.
> > >
> > > The weird thing is that it tags them (in the security log) as coming >
> > from the master address (not the alias) out the correct interface. In a >
> > normal world that would mean the packet would match!!!!!
> > > > What's goin' on here Willis?
> > Difficult to tell without seeing a) ifconfig b) netstat -rn c) at least the
> > relevant firewall rule/s and d) log entries that illustrate your problem.
> > Obscure sensitive information by all means, but otherwise pretend we
> > haven't the slightest clue how your system is configured :)
> Fair enough.
> ifconfig below:
> bce1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
> inet 184.108.40.206 netmask 0xffffffe0 broadcast 220.127.116.11
> inet 18.104.22.168 netmask 0xffffffff broadcast 22.214.171.124
> inet 126.96.36.199 netmask 0xffffffff broadcast 188.8.131.52
> inet 184.108.40.206 netmask 0xffffffff broadcast 220.127.116.11
> inet 18.104.22.168 netmask 0xffffffff broadcast 22.214.171.124
> inet 126.96.36.199 netmask 0xffffffff broadcast 188.8.131.52
> inet 184.108.40.206 netmask 0xffffffff broadcast 220.127.116.11
> ether 00:1c:c4:c0:56:94
> media: Ethernet autoselect (1000baseSX <full-duplex>)
> status: active
> Relevant /etc/rc.conf entries :
> ifconfig_bce1="inet 18.104.22.168 netmask 255.255.255.224"
> ifconfig_bce1_alias0="inet 22.214.171.124 netmask 255.255.255.224"
Your first alias here is a repeat of the 'primary' address. ifonfig
seems to have resolved/merged that above, but it's not an alias.
> ifconfig_bce1_alias1="inet 126.96.36.199 netmask 255.255.255.255"
> ifconfig_bce1_alias2="inet 188.8.131.52 netmask 255.255.255.255"
> ifconfig_bce1_alias3="inet 184.108.40.206 netmask 255.255.255.255"
> ifconfig_bce1_alias4="inet 220.127.116.11 netmask 255.255.255.255"
> ifconfig_bce1_alias5="inet 18.104.22.168 netmask 255.255.255.255"
> ifconfig_bce1_alias6="inet 22.214.171.124 netmask 255.255.255.255"
I didn't spot on first reading this that the first address is in a
different subnet than all the others. I'm not entirely sure whether
that's relevant, or how, just pointing it out as being non-obvious, and
suspecting one of the 210.5.51 subnet should show a broader netmask.
> Relevant ipfw rules :
> ipfw -q add 02012 allow tcp from any to 126.96.36.199 80 out via bce1 setup
> ipfw -q add 02012 allow tcp from any to 188.8.131.52 443 out via bce1 setup
netstat -finet -rn (or -rna) please? unclear where your default route
goes, or how the 210.5.51 subnet is routed or its netmask, but assume
that 184.108.40.206 is probably accessed via the default route ..
> Interesting entries in /var/log/security :
> Dec 1 16:42:25 <servername> kernel: ipfw: 9999 Deny TCP 220.127.116.11:49708
> 18.104.22.168:80 out via bce1
Did that occur =after= the above rules were installed? Just the one?
Seems odd on face value, but without knowing what your other rules do.
> What makes this interesting is that I can connect to that port via the
> command line.
You mean like with 'telnet 22.214.171.124 80' ? With 126.96.36.199 as
source address? tcpdump output may help understand or explain this.
> It's the website that lives on 188.8.131.52 that is having problems. Why, if
> the rule is valid enough for the command line is it having problems from an
> aliased address?
Hang on; do you mean you're having a webserver on 184.108.40.206 trying to
connect out to another webserver on 220.127.116.11 ? If not, what?
I guess you have rules allowing inbound port 80 access to 18.104.22.168 ?
And that your upstream is routing 22.214.171.124/something to 126.96.36.199 ?
> This MUST have something to do with the way ipfw is working with aliased
> addresses but I'm blowed if I know what is wrong.
ipfw doesn't do anything different with any address in particular except
when using the forward action. ipfw certainly has no concept of primary
or alias addresses, it just applies the addresses/masks you specify.
Nor does ipfw know or care (even when forwarding) whence the stack is
next going to route outbound packets .. but netstat -rn will tell us.
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