Date: Tue, 12 Mar 2019 13:19:21 -0600 From: James Gritton <jamie@gritton.org> To: freebsd-jail@freebsd.org Subject: Re: exec.fib and a jail in two subnets Message-ID: <6a245a1f51270c71d1da07c55ef51113@gritton.org> In-Reply-To: <eae383df-72d4-0fe8-6613-cf34417e2260@gjunka.com> References: <eae383df-72d4-0fe8-6613-cf34417e2260@gjunka.com>
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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.
- Jamie
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