Users Guide

• If a packet's FO > 0, the packet is permitted
• If a packet's FO = 0, the next ACL entry processes
Deny ACL with L3 information only
If a packet's L3 information does not match the L3 information in the ACL, the packet's FO is checked:
• If a packet's FO > 0, the packet is denied
• If a packet's FO = 0, the next ACL line processes
Permit all packets from host
OS10(config)# ip access-list ABC
OS10(conf-ipv4-acl)# permit tcp host 10.1.1.1 any eq 24
OS10(conf-ipv4-acl)# deny ip any any fragment
Permit only first fragments and non-fragmented packets
from host
OS10(config)# ip access-list ABC
OS10(conf-ipv4-acl)# permit tcp host 10.1.1.1 any eq 24
OS10(conf-ipv4-acl)# permit tcp host 10.1.1.1 any fragment
OS10(conf-ipv4-acl)# deny ip any any fragment
To log all packets denied and to override the implicit deny rule and the implicit permit rule for TCP/ UDP fragments, use a similar
configuration. When an ACL filters packets, it looks at the FO to determine whether it is a fragment:
• FO = 0 means it is either the first fragment or the packet is a non-fragment
• FO > 0 means it is the fragments of the original packet
Assign sequence number to filter
IP ACLs filter on source and destination IP addresses, IP host addresses, TCP addresses, TCP host addresses, UDP addresses, and UDP
host addresses. Traffic passes through the filter by filter sequence. Configure the IP ACL by first entering IP ACCESS-LIST mode and
then assigning a sequence number to the filter.
User-provided sequence number
• Enter IP ACCESS LIST mode by creating an IP ACL in CONFIGURATION mode.
ip access-list access-list-name
• Configure a drop or forward filter in IPV4-ACL mode.
seq sequence-number {deny | permit | remark} {ip-protocol-number | icmp | ip | protocol |
tcp | udp} {
source prefix | source mask | any | host} {destination mask | any | host ip-
address} [count [byte]] [fragments]
Auto-generated sequence number
If you are creating an ACL with only one or two filters, you can let the system assign a sequence number based on the order you configure
the filters. The system assigns sequence numbers to filters using multiples of ten values.
• Configure a deny or permit filter to examine IP packets in IPV4-ACL mode.
{deny | permit} {source mask | any | host ip-address} [count [byte]] [fragments]
Access Control Lists
1021