01-23-2009
Easy way to check it to use telnet.
To check if you can communicate with a internal mail server do the following.
from external pc.
telnet (Ip address of public nic on router) 25
eg. telnet 192.168.0.55 25
for a pop3 server connection change 25 to 110 and so on.
If you look at your firewall rules there must be a rule that says something along these lines.
"Allow in coming traffic from anywhere on port 22 to local ip address."
Now i assume that your internet router has a ipaddress on the local nic and one on the ppp+ port. So lets say your internal ip address is 192.168.0.254 and the ppp+ address is 42.253.200.110 (Assigned by your isp). now to allow a connection on port 22 (ssh) from the outside world you need to make a rule in your firewall that says this.
allow tcp traffic from anywhere on port 22 to 42.253.200.110. (Not sure what router you use).
If you have a internal server with ip address 192.168.0.115 that is separate from the router running a vnc service you would do something along these lines.
allow tcp traffic from anywhere on port 5900 to internal server 192.168.0.115
Then always remember to deny everything else from coming in as the last rule.
Hope this helps
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LEARN ABOUT DEBIAN
shorewall-exclusion
SHOREWALL-EXCLUSION(5) [FIXME: manual] SHOREWALL-EXCLUSION(5)
NAME
exclusion - Exclude a set of hosts from a definition in a shorewall configuration file.
SYNOPSIS
!address-or-range[,address-or-range]...
!zone-name[,zone-name]...
DESCRIPTION
The first form of exclusion is used when you wish to exclude one or more addresses from a definition. An exclaimation point is followed by
a comma-separated list of addresses. The addresses may be single host addresses (e.g., 192.168.1.4) or they may be network addresses in
CIDR format (e.g., 192.168.1.0/24). If your kernel and iptables include iprange support, you may also specify ranges of ip addresses of the
form lowaddress-highaddress
No embedded whitespace is allowed.
Exclusion can appear after a list of addresses and/or address ranges. In that case, the final list of address is formed by taking the first
list and then removing the addresses defined in the exclusion.
Beginning in Shorewall 4.4.13, the second form of exclusion is allowed after all and any in the SOURCE and DEST columns of
/etc/shorewall/rules. It allows you to omit arbitrary zones from the list generated by those key words.
Warning
If you omit a sub-zone and there is an explicit or explicit CONTINUE policy, a connection to/from that zone can still be matched by the
rule generated for a parent zone.
For example:
/etc/shorewall/zones:
#ZONE TYPE
z1 ip
z2:z1 ip
...
/etc/shorewall/policy:
#SOURCE DEST POLICY
z1 net CONTINUE
z2 net REJECT
/etc/shorewall/rules:
#ACTION SOURCE DEST PROTO DEST
# PORT(S)
ACCEPT all!z2 net tcp 22
In this case, SSH connections from z2 to net will be accepted by the generated z1 to net ACCEPT rule.
In most contexts, ipset names can be used as an address-or-range. Beginning with Shorewall 4.4.14, ipset lists enclosed in +[...] may also
be included (see shorewall-ipsets[1] (5)). The semantics of these lists when used in an exclusion are as follows:
o !+[set1,set2,...setN] produces a packet match if the packet does not match at least one of the sets. In other words, it is like NOT
match set1 OR NOT match set2 ... OR NOT match setN.
o +[!set1,!set2,...!setN] produces a packet match if the packet does not match any of the sets. In other words, it is like NOT match set1
AND NOT match set2 ... AND NOT match setN.
EXAMPLES
Example 1 - All IPv4 addresses except 192.168.3.4
!192.168.3.4
Example 2 - All IPv4 addresses except the network 192.168.1.0/24 and the host 10.2.3.4
!192.168.1.0/24,10.1.3.4
Example 3 - All IPv4 addresses except the range 192.168.1.3-192.168.1.12 and the network 10.0.0.0/8
!192.168.1.3-192.168.1.12,10.0.0.0/8
Example 4 - The network 192.168.1.0/24 except hosts 192.168.1.3 and 192.168.1.9
192.168.1.0/24!192.168.1.3,192.168.1.9
Example 5 - All parent zones except loc
any!loc
FILES
/etc/shorewall/hosts
/etc/shorewall/masq
/etc/shorewall/rules
/etc/shorewall/tcrules
SEE ALSO
shorewall(8), shorewall-accounting(5), shorewall-actions(5), shorewall-blacklist(5), shorewall-hosts(5), shorewall_interfaces(5),
shorewall-ipsets(5), shorewall-maclist(5), shorewall-masq(5), shorewall-nat(5), shorewall-netmap(5), shorewall-params(5),
shorewall-policy(5), shorewall-providers(5), shorewall-proxyarp(5), shorewall-rtrules(5), shorewall-routestopped(5), shorewall-rules(5),
shorewall.conf(5), shorewall-secmarks(5), shorewall-tcclasses(5), shorewall-tcdevices(5), shorewall-tcrules(5), shorewall-tos(5),
shorewall-tunnels(5), shorewall-zones(5)
NOTES
1. shorewall-ipsets
http://www.shorewall.net/manpages/shorewall-ipsets.html
[FIXME: source] 06/28/2012 SHOREWALL-EXCLUSION(5)