Security 10-25
1.
The rule you want to implement as a filter is:
Block all Telnet attempts that originate from the remote host 199.211.211.17.
2.
The host 199.211.211.17 is the source of the Telnet packets you want to block, while the destination
address is any IP address. How these IP addresses are masked determines what the final match will be,
although the mask is not displayed in the table that displays the filter sets (you set it when you create the
filter). In fact, since the mask for the destination IP address is 0.0.0.0, the address for Dest IP Addr could
have been anything. The mask for Source IP Addr must be 255.255.255.255 since an exact match is
desired.
•
Source IP Addr = 199.211.211.17
•
Source IP address mask = 255.255.255.255
•
Dest IP Addr = 0.0.0.0
•
Destination IP address mask = 0.0.0.0
3.
Using the tables on
page 10-22
, find the destination por t and protocol numbers (the
local
Telnet por t):
•
Proto = TCP (or 6)
•
D. Por t = 23
4.
The filter should be enabled and instructed to block the Telnet packets containing the source address
shown in step 2:
•
On? = Yes
•
Fwd = No
This four-step process is how we produced the following filter from the original rule:
Filtering example #2
Suppose a filter is configured to block all incoming IP packets with the source IP address of 200.233.14.0,
regardless of the type of connection or its destination. The filter would look like this:
This filter blocks any packets coming from a remote network with the IP network address 200.233.14.0. The 0
at the end of the address signifies
any
host on the class C IP network 200.233.14.0. If, for example, the filter
is applied to a packet with the source IP address 200.233.14.5, it will block it.
+-#---Source IP Addr---Dest IP Addr-----Proto-Src.Port-D.Port--On?-Fwd-+
+----------------------------------------------------------------------+
| 1 192.211.211.17 0.0.0.0 TCP 0 23 Yes No |
| |
+----------------------------------------------------------------------+
+-#---Source IP Addr---Dest IP Addr-----Proto-Src.Port-D.Port--On?-Fwd-+
+----------------------------------------------------------------------+
| 1 200.233.14.0 0.0.0.0 0 Yes No |
| |
+----------------------------------------------------------------------+
Summary of Contents for Netopia Embedded Software
Page 10: ...x Administrator s Handbook ...
Page 16: ...1 6 Administrator s Handbook ...
Page 44: ...2 28 Administrator s Handbook ...
Page 108: ...3 64 Administrator s Handbook ...
Page 176: ...5 34 Administrator s Handbook ...
Page 202: ...6 26 Administrator s Handbook ...
Page 244: ...7 42 Administrator s Handbook ...
Page 340: ...Index 6 ...