White Papers

CONFIGURATION mode
ip access-list extended access-list-name
2. Configure a drop or forward filter.
CONFIG-EXT-NACL mode
seq sequence-number {deny | permit} {ip-protocol-number | icmp | ip | tcp | udp} {source
mask | any | host ip-address} {destination mask | any | host ip-address} [operator port
[port]] [count [byte]] [order] [fragments]
When you create the filters with a specific sequence number, you can create the filters in any order and the filters are placed in
the correct order.
NOTE: When assigning sequence numbers to filters, you might need to insert a new filter. To prevent reconfiguring multiple
filters, assign sequence numbers in multiples of five or another number.
The following examples shows how the seq command orders the filters according to the sequence number assigned. In the
example, filter 15 was configured before filter 5, but the show config command displays the filters in the correct order.
Dell(conf-ext-nacl)#seq 15 deny ip host 112.45.0.0 any
Dell(conf-ext-nacl)#seq 5 permit tcp 12.1.3.45 255.255.0.0 any
Dell(conf-ext-nacl)#show config
!
ip access-list extended dilling
seq 5 permit tcp 12.1.0.0 255.255.0.0 any
seq 15 deny ip host 112.45.0.0 any
Dell(conf-ext-nacl)#
Configuring Filters Without a Sequence Number
If you are creating an extended ACL with only one or two filters, you can let the system assign a sequence number based on the
order in which the filters are configured. The system assigns filters in multiples of five.
To configure a filter for an extended IP ACL without a specified sequence number, use any or all of the following commands:
● Configure a deny or permit filter to examine IP packets.
CONFIG-EXT-NACL mode
{deny | permit} {source mask | any | host ip-address} [count [byte]] [order] [fragments]
● Configure a deny or permit filter to examine TCP packets.
CONFIG-EXT-NACL mode
{deny | permit} tcp {source mask] | any | host ip-address}} [count [byte]] [order]
[fragments]
● Configure a deny or permit filter to examine UDP packets.
CONFIG-EXT-NACL mode
{deny | permit} udp {source mask | any | host ip-address}} [count [byte]] [order]
[fragments]
The following example shows an extended IP ACL in which the sequence numbers were assigned by the software. The filters
were assigned sequence numbers based on the order in which they were configured (for example, the first filter was given the
lowest sequence number). The show config command in IP ACCESS LIST mode displays the two filters with the sequence
numbers 5 and 10.
Dell(config-ext-nacl)#deny tcp host 123.55.34.0 any
Dell(config-ext-nacl)#permit udp 154.44.123.34 0.0.255.255 host 34.6.0.0
Dell(config-ext-nacl)#show config
!
ip access-list extended nimule
seq 5 deny tcp host 123.55.34.0 any
seq 10 permit udp 154.44.0.0 0.0.255.255 host 34.6.0.0
Dell(config-ext-nacl)#
To view all configured IP ACLs and the number of packets processed through the ACL, use the show ip accounting
access-list command in EXEC Privilege mode, as shown in the first example in Configuring a Standard IP ACL Filter.
Access Control Lists (ACLs)
109