Configuration Guide User guide

FastIron Configuration Guide 1395
53-1002494-02
Filtering
NOTE
Once you define a filter, the default action for addresses that do not match a filter is “deny”. To
change the default action to “permit”, configure the last filter as “permit any any”.
The <ip-addr> parameter specifies the IP address. If you want the filter to match on all addresses,
enter any.
The <wildcard> parameter specifies the portion of the IP address to match against. The <wildcard>
is in dotted-decimal notation (IP address format). It is a four-part value, where each part is 8 bits
(one byte) separated by dots, and each bit is a one or a zero. Each part is a number ranging from 0
to 255, for example 0.0.0.255. Zeros in the mask mean the packet source address must match the
<source-ip>. Ones mean any value matches. For example, the
<ip-addr> and <wildcard> values 209.157.22.26 0.0.0.255 mean that all hosts in the Class C
subnet 209.157.22.x match the policy.
If you prefer to specify the wildcard (mask value) in Classless Interdomain Routing (CIDR) format,
you can enter a forward slash after the IP address, then enter the number of significant bits in the
mask. For example, you can enter the CIDR equivalent of “209.157.22.26 0.0.0.255” as
“209.157.22.26/24”. The CLI automatically converts the CIDR number into the appropriate mask
(where zeros instead of ones are the significant bits) and changes the non-significant portion of the
IP address into zeros. For example, if you specify 209.157.22.26/24 or 209.157.22.26 0.0.0.255,
then save the changes to the startup-config file, the value appears as 209.157.22.0/24 (if you
have enabled display of subnet lengths) or 209.157.22.0 0.0.0.255 in the startup-config file.
If you enable the software to display IP subnet masks in CIDR format, the mask is saved in the file
in “/<mask-bits>” format. To enable the software to display the CIDR masks, enter the ip
show-subnet-length command at the global CONFIG level of the CLI. You can use the CIDR format to
configure the filter regardless of whether the software is configured to display the masks in CIDR
format.
The <mask> parameter specifies the network mask. If you want the filter to match on all
destination addresses, enter any. The wildcard works the same as described above.
AS-path filtering
You can filter updates received from BGP4 neighbors based on the contents of the AS-path list
accompanying the updates. For example, if you want to deny routes that have the AS 4.3.2.1 in the
AS-path from entering the BGP4 route table, you can define a filter to deny such routes.
The Layer 3 switch provides the following methods for filtering on AS-path information:
• AS-path filters
• AS-path ACLs
NOTE
The Layer 3 switch cannot actively support AS-path filters and AS-path ACLs at the same time. Use
one method or the other but do not mix methods.
NOTE
Once you define a filter or ACL, the default action for updates that do not match a filter is “deny”. To
change the default action to “permit”, configure the last filter or ACL as “permit any any”.
AS-path filters or AS-path ACLs can be referred to by a BGP neighbor's filter list number as well as
by match statements in a route map.