Administrator Guide

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. Filters are assigned 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]
When you use the log keyword, the CP logs details about the packets that match. Depending on how many packets match the
log entry and at what rate, the CP may become busy as it has to log these packets’ details.
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 Configure a Standard IP ACL Filter.
Configure Layer 2 and Layer 3 ACLs
Both Layer 2 and Layer 3 ACLs may be configured on an interface in Layer 2 mode.
If both L2 and L3 ACLs are applied to an interface, the following rules apply:
● When the system routes the packets, only the L3 ACL governs them because they are not filtered against an L2 ACL.
● When the system switches the packets, first the L3 ACL filters them, then the L2 ACL filters them.
● When the system switches the packets, the egress L3 ACL filters the packet.
For the following features, if you enable counters on rules that have already been configured and a new rule is either inserted or
prepended, all the existing counters are reset:
● L2 ingress access list
● L3 egress access list
● L2 egress access list
If a rule is simply appended, existing counters are not affected.
Table 6. L2 and L3 Filtering on Switched Packets
L2 ACL Behavior L3 ACL Behavior Decision on Targeted Traffic
Deny Deny L3 ACL denies.
Deny Permit L3 ACL permits.
Access Control Lists (ACLs) 117