Kernel NAT issues

Nathan Aherne nathan at reddog.com.au
Fri Nov 20 23:12:23 UTC 2015


I am not exactly sure how to draw the setup so it doesn’t confuse the situation. The setup is extremely simple (I am not running vimage), jails running on the 10.0.0.0/16 (cloned lo1 interface) network or with public IPs. The jails with private IPs are the HTTP app jails. The Host runs a HTTP Proxy (nginx) and forwards traffic to each HTTP App jail based on the URL it receives. The jails with public IPs are things like database jails which cannot be proxied by the Host.

I can happily communicate with any jail from my laptop (externally) but when I want one jail to communicate with another jail (for example an App Jail communicating with the database jail) the traffic shows as backwards (destination:port -> source:port) in the IPFW logs (tshark shows the traffic correctly source:port -> destination:port). The jail to jail traffic tries to go over the lo1 interface (backwards) and is blocked. Below is some IPFW logs of an App jail (10.0.0.25) communicating with the database jail (aaa.bbb.ccc.ddd)

IPFW logs. The lines labelled UNKNOWN is the check-state rule (everything is labelled UNKNOWN even if it is KNOWN traffic)

Nov 21 08:49:07 host5 kernel: ipfw: 101 UNKNOWN TCP eee.fff.gg.hhh:5432 10.0.0.25:42957 out via lo1
Nov 21 08:49:07 host5 kernel: ipfw: 65501 Deny TCP eee.fff.gg.hhh:5432 10.0.0.25:42957 out via lo1
Nov 21 08:49:10 host5 kernel: ipfw: 101 UNKNOWN TCP eee.fff.gg.hhh:5432 10.0.0.25:42957 out via lo1
Nov 21 08:49:10 host5 kernel: ipfw: 65501 Deny TCP eee.fff.gg.hhh:5432 10.0.0.25:42957 out via lo1
Nov 21 08:49:13 host5 kernel: ipfw: 101 UNKNOWN TCP eee.fff.gg.hhh:5432 10.0.0.25:42957 out via lo1
Nov 21 08:49:13 host5 kernel: ipfw: 65501 Deny TCP eee.fff.gg.hhh:5432 10.0.0.25:42957 out via lo1
Nov 21 08:49:16 host5 kernel: ipfw: 101 UNKNOWN TCP eee.fff.gg.hhh:5432 10.0.0.25:42957 out via lo1
Nov 21 08:49:16 host5 kernel: ipfw: 65501 Deny TCP eee.fff.gg.hhh:5432 10.0.0.25:42957 out via lo1

tshark output (loopback and wan interface capture for port 5432)

Capturing on 'Loopback' and 'bce0'
  1   0.000000    10.0.0.25 -> eee.fff.gg.hhh TCP 64 42957→5432 [SYN] Seq=0 Win=65535 Len=0 MSS=16344 WS=64 SACK_PERM=1 TSval=142885525 TSecr=0
  2   3.013905    10.0.0.25 -> eee.fff.gg.hhh TCP 64 [TCP Retransmission] 42957→5432 [SYN] Seq=0 Win=65535 Len=0 MSS=16344 WS=64 SACK_PERM=1 TSval=142888539 TSecr=0
  3   6.241658    10.0.0.25 -> eee.fff.gg.hhh TCP 64 [TCP Retransmission] 42957→5432 [SYN] Seq=0 Win=65535 Len=0 MSS=16344 WS=64 SACK_PERM=1 TSval=142891767 TSecr=0
  4   9.451516    10.0.0.25 -> eee.fff.gg.hhh TCP 64 [TCP Retransmission] 42957→5432 [SYN] Seq=0 Win=65535 Len=0 MSS=16344 WS=64 SACK_PERM=1 TSval=142894976 TSecr=0
  5  12.654656    10.0.0.25 -> eee.fff.gg.hhh TCP 64 [TCP Retransmission] 42957→5432 [SYN] Seq=0 Win=65535 Len=0 MSS=16344 WS=64 SACK_PERM=1 TSval=142898180 TSecr=0
  6  15.863900    10.0.0.25 -> eee.fff.gg.hhh TCP 64 [TCP Retransmission] 42957→5432 [SYN] Seq=0 Win=65535 Len=0 MSS=16344 WS=64 SACK_PERM=1 TSval=142901389 TSecr=0
  7  22.076655    10.0.0.25 -> eee.fff.gg.hhh TCP 64 [TCP Retransmission] 42957→5432 [SYN] Seq=0 Win=65535 Len=0 MSS=16344 WS=64 SACK_PERM=1 TSval=142907602 TSecr=0


> If so, what sort of routing is setup on both host and jails?

Routing is what would be added by default (whatever the host system adds when adding an IP), there is no custom routing. I have wondered if I need to modify the routing table to get this to work. 

Below is the output of netstat -rn

www.xxx.yy.zzz is the gateway address
eee.fff.gg.hhh is the database jail public IP
aaa.bbb.cc.ddd is the public IP for NAT
lll.mmm.nn.ooo is the Hosts public IP


Routing tables

Internet:
Destination        Gateway            Flags      Netif Expire
default            www.xxx.yy.zzz     UGS        bce0
10.0.0.1           link#6             UH          lo1
10.0.0.2           link#6             UH          lo1
10.0.0.3           link#6             UH          lo1
10.0.0.4           link#6             UH          lo1
10.0.0.5           link#6             UH          lo1
10.0.0.6           link#6             UH          lo1
10.0.0.7           link#6             UH          lo1
10.0.0.8           link#6             UH          lo1
10.0.0.9           link#6             UH          lo1
10.0.0.10          link#6             UH          lo1
10.0.0.11          link#6             UH          lo1
10.0.0.12          link#6             UH          lo1
10.0.0.13          link#6             UH          lo1
10.0.0.14          link#6             UH          lo1
10.0.0.15          link#6             UH          lo1
10.0.0.16          link#6             UH          lo1
10.0.0.17          link#6             UH          lo1
10.0.0.18          link#6             UH          lo1
10.0.0.19          link#6             UH          lo1
10.0.0.20          link#6             UH          lo1
10.0.0.21          link#6             UH          lo1
10.0.0.22          link#6             UH          lo1
10.0.0.23          link#6             UH          lo1
10.0.0.24          link#6             UH          lo1
10.0.0.25          link#6             UH          lo1
10.0.0.26          link#6             UH          lo1
www.xxx.yy.zzz/25  link#1             U          bce0
eee.fff.gg.hhh     link#1             UHS         lo0
eee.fff.gg.hhh/32  link#1             U          bce0
aaa.bbb.cc.ddd     link#1             UHS         lo0
aaa.bbb.cc.ddd/32  link#1             U          bce0
lll.mmm.nn.ooo     link#1             UHS         lo0
127.0.0.1          link#5             UH          lo0

Internet6:
Destination                       Gateway                       Flags      Netif Expire
::/96                             ::1                           UGRS        lo0
::1                               link#5                        UH          lo0
::ffff:0.0.0.0/96                 ::1                           UGRS        lo0
fe80::/10                         ::1                           UGRS        lo0
fe80::%lo0/64                     link#5                        U           lo0
fe80::1%lo0                       link#5                        UHS         lo0
ff01::%lo0/32                     ::1                           U           lo0
ff02::/16                         ::1                           UGRS        lo0
ff02::%lo0/32                     ::1                           U           lo0

> Anything like ?
> http://kb.juniper.net/InfoCenter/index?page=content&id=KB24639&actp=search <http://kb.juniper.net/InfoCenter/index?page=content&id=KB24639&actp=search>
Yes just like that.

Regards,

Nathan

> On 19 Nov 2015, at 2:46 am, Ian Smith <smithi at nimnet.asn.au> wrote:
> 
> On Wed, 18 Nov 2015 22:17:29 +0800, Julian Elischer wrote:
>> On 11/18/15 8:40 AM, Nathan Aherne wrote:
>>> For some reason hairpin (loopback nat or nat reflection) does not seem to
>>> be working, which is why I chose IPFW in the first place.
> 
>> it would be good to see a diagram of what this actually means.
> 
> Anything like ?
> http://kb.juniper.net/InfoCenter/index?page=content&id=KB24639&actp=search
> 
> Was this so one jail can only access service/s provided by other jail/s, 
> both/all with internal NAT'd addresses, by using only the public address 
> and port of the 'router', which IIRC this is a single system with jails?
> 
> If so, what sort of routing is setup on both host and jails?
> 
> (blindfolded, no idea where I've pinned the donkey's tail :)
> 
> cheers, Ian



More information about the freebsd-ipfw mailing list