Tom Eastep wrote:
> Trent O'Callaghan wrote:
>> MASQ/SNAT and ARP are interacting in a way that is causing outbound
>> connectivity issues in periods of low traffic (when ARP entries timeout). 
>> Tcpdump of ARP packets shows who-has packets with the SNAT IP address when I
>> need them to have the Firewall's Interface IP address as their source.
>>
>> I have modified MASQ to SNAT to the Firewall's Interface IP address for the
>> Peering network (via 198.32.212.73), but outbound traffic is normally to
>> more distant networks and my default route is to the Paid Internet (via
>> 121.200.226.210).
>>
>> I have seen some have scripted ARP watchers that could assist but I believe
>> this is something Shorewall can cope with, but I am lacking in the
>> knowledge.
>>
>> r...@per-r1:/etc/shorewall# ifconfig -a
>> eth0      Link encap:Ethernet  HWaddr 00:15:17:cc:dd:90
>>           inet addr:121.200.226.210  Bcast:121.200.226.211
>> Mask:255.255.255.252
>> eth0:1    Link encap:Ethernet  HWaddr 00:15:17:cc:dd:90
>>           inet addr:198.32.212.73  Bcast:198.32.212.255  Mask:255.255.255.0
>> eth0:2    Link encap:Ethernet  HWaddr 00:15:17:cc:dd:90
>>           inet addr:180.233.131.7  Bcast:180.233.131.255  Mask:255.255.255.0
>> eth1      Link encap:Ethernet  HWaddr 00:15:17:cc:dd:91
>>           inet addr:10.240.0.1  Bcast:10.240.0.255  Mask:255.255.255.0
>>
>> r...@per-r1:/etc/shorewall# ip route show table main | grep -v zebra
>> 121.200.226.208/30 dev eth0  proto kernel  scope link  src 121.200.226.210
>> 198.32.212.0/24 dev eth0  proto kernel  scope link  src 198.32.212.73
>> 180.233.131.0/24 dev eth0  proto kernel  scope link  src 180.233.131.7
>> 10.240.1.0/24 dev eth1  proto kernel  scope link  src 10.240.1.1
>> default via 121.200.226.209 dev eth0  metric 100
>>
>> #
>> # Shorewall version 4 - Masq file
>> #
>> eth0:!198.32.212.0/24   eth1:!10.240.1.7        180.233.131.7
> 
> Ah! I took one more look at your report and I seriously doubt that the
> above rule does what you expect. Rewrite it as:
> 
> eth0:!198.32.212.0/24    10.240.0.0/24!10.240.1.7

In fact, the current version of Shorewall (4.4.6) rejects that type of rule:

gateway:/etc/shorewall# shorewall check
Compiling...
   WARNING: Using an interface as the masq SOURCE requires the interface
to be up and configured when Shorewall starts/restarts :
/etc/shorewall/masq (line 7)
   ERROR: SOURCE interface may not be specified with a source IP address
in the POSTROUTING chain : /etc/shorewall/masq (line 7)
gateway:/etc/shorewall#

Are you still using Shorewall-shell? If so, I highly recommend migrating
to Shorewall-perl at the first opportunity. It does a much better job of
validating the configuration at compile-time (and it does it much faster
as well).

-Tom
-- 
Tom Eastep        \ When I die, I want to go like my Grandfather who
Shoreline,         \ died peacefully in his sleep. Not screaming like
Washington, USA     \ all of the passengers in his car
http://shorewall.net \________________________________________________

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