Date: Tue, 12 Mar 2019 20:05:34 +0000 From: Grzegorz Junka <list1@gjunka.com> To: James Gritton <jamie@gritton.org>, freebsd-jail@freebsd.org Subject: Re: exec.fib and a jail in two subnets Message-ID: <e25f8982-2739-1622-0fac-c3548a7f2255@gjunka.com> In-Reply-To: <6a245a1f51270c71d1da07c55ef51113@gritton.org> References: <eae383df-72d4-0fe8-6613-cf34417e2260@gjunka.com> <6a245a1f51270c71d1da07c55ef51113@gritton.org>
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On 12/03/2019 19:19, James Gritton wrote:
> On 2019-03-10 13:40, Grzegorz Junka wrote:
>> Hi,
>>
>> I am not sure if this question fits better to net or jail list so
>> please delete one crosspost when replying.
>>
>> I have two routers in separate subnets (say 10.0.0.0/16 and
>> 172.16.0.0/16). I have enabled multiple fibs on the host and I am
>> trying to setup a jail so that packets from one router are returned to
>> the same router. The second subnet is configured like this:
>>
>> setfib 1 route add -net 172.16.0.0/16 -iface lagg0
>> setfib 1 route add default 172.16.0.1
>>
>> When the jail configuration is (differences in red):
>>
>> mta {
>> exec.fib=1;
>> ip4.addr = 172.16.0.2;
>> interface = lagg0;
>> }
>>
>> router 172.16.0.1 is able to send to and receive packets from the jail
>> as expected.
>>
>> When the jail configuration is:
>>
>> mta {
>> ip4.addr = 10.0.0.2,172.16.0.2;
>> interface = lagg0;
>> }
>>
>> then router 10.0.0.1 is also able to send and receive packets from the
>> jail as expected.
>>
>> However, when the configuration is:
>>
>> mta {
>> exec.fib=1;
>> ip4.addr = 10.0.0.2,172.16.0.2;
>> interface = lagg0;
>> }
>>
>> then router 172.16.0.1 is no longer able to receive a response from
>> the jail. The router's event log shows entry similar to the following
>> two about 2 minutes apart:
>>
>> IN: ACCEPT [54] Connection opened (Port Forwarding: TCP
>> [172.16.0.2]:80 <--> [212.159.95.213]:80 - - -
>> [111.202.101.2]:34172 CLOSED/SYN_SENT ppp3 NAPT)
>> IN: ACCEPT [57] Connection closed (Port Forwarding: TCP
>> [172.16.0.2]:80 <--> [212.159.95.213]:80 - - -
>> [111.202.101.2]:34172 CLOSED/SYN_SENT ppp3 NAPT)
>>
>> My question is why the 10.0.0.1 router is able to communicate with the
>> jail in the second configuration but 172.16.0.1 is not able to
>> communicate with the jail in the third configuration. Is it because of
>> order of IPs in ip4.addr?
>>
>> When the jail is started jls shows only the first IP from either of
>> the configuration list above (i.e. 10.0.0.2 even if exec.fib is set to
>> 1). So my guess is that the first IP is somehow a default IP?
>>
>> Then my additional question is if it's possible for a jail to be in
>> two subnets at the same time, i.e. so that when the jail responds to a
>> packet received from router 10.0.0.1 it sends it to the default route
>> from fib0 and when it responds to a packet received from 172.16.0.1 it
>> sends it to the default route from fib1. What exec.fib should be in
>> such a case?
>>
>> Any help would be greatly appreciated. Thanks!
>
> You're correct in your assumption that a jail's first IP address is
> its default: in the absence of binding a particular address for an
> outgoing connection, the first-listed address will be used. So then
> the problem with the third jail is you have a packing being sent from
> 10.0.0.2 with only the routing table that doesn't include 10.0/16. I
> can't say exactly why your second example *does* work, but at least
> from the jail side it has a default address that's reachable in its
> routing table. I'm thinking you're saying that the second jail works
> not only with 10.0 but also with 172.16 (it's the 172.16 part I'm
> unsure about).
>
> To answer your last question: sure, a jail can be in two subnets - but
> it will still use its first address by default for any outbound
> packets. Note that the FIB associated with the jail isn't *really*
> associated with the jail, but with the processes jail(8) starts for it
> - the reason for the "exec" in "exec.fib". You're still free to call
> setfib from inside the jail to access a different table.
>
> I haven't tried using two different routing tables in one jail at the
> same time; the closest I've come is one jail that routed on the
> non-default network. Outside of the jail world, I believe multiple
> routing tables implies multiple instances of servers, and that would
> be the same for inside a jail. Your router log shows port 80, so that
> would imply two different apache (or whatever) processes running the
> jail, each pointing to its own address, and rung under its own routing
> table.
>
Many thanks for your response. The second example works with 10.0.0.1
but not with 172.16.0.1, otherwise there would be no post. Following on
your response, lets assume that a process (e.g. nginx) listens on both
IPs, 10.0.0.2,172.16.0.2. Is it possible to configure fibs or default
routes or whatever so that when a packet arrives from 10.0.0.1 it is
send back to 10.0.0.1 and if it arrives from 172.16.0.1 it is send back
to 172.16.0.1 (thus using default routes from either fib0 or fib1
depending if the packet came from a router in one of those network)? If
not, would it be possible to do this with some iptables/pf rules (which
I understand in FreeBSD 12 should work in a jail with VNET)?
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