Reference Guide

NOTE: Hot lock ACLs are supported for ingress ACLs only.
MAC ACLs
MAC ACLs lter trac on the L2 header of a packet. This trac ltering is based on:
Source MAC packet
address
MAC address range (address mask in 3x4 dotted hexadecimal notation), and any to denote that the rule matches
all source addresses.
Destination MAC
packet address
MAC address range (address-mask in 3x4 dotted hexadecimal notation), and any to denote that the rule matches
all destination addresses.
Packet protocol Set by its EtherType eld contents and Assigned protocol number for all protocols.
VLAN ID Set in the packet header
Class of service
(CoS)
Present in the packet header
IPv4/IPv6 and MAC ACLs apply separately for inbound and outbound packets. You can assign an interface to multiple ACLs, with a limit of
one ACL per packet direction per ACL type.
IP fragment handling
OS10 supports a congurable option to explicitly deny IP fragmented packets, particularly for the second and subsequent packets. This
option extends the existing ACL command syntax with the fragments keyword for all Layer 3 (L3) rules:
• Second and subsequent fragments are allowed because you cannot apply a L3 rule to these fragments. If the packet is to be denied
eventually, the rst fragment must be denied and the packet as a whole cannot be reassembled.
• The system applies implicit permit for the second and subsequent fragment prior to the implicit deny.
• If you congure an explicit deny, the second and subsequent fragments do not hit the implicit permit rule for fragments.
IP fragments ACL
When a packet exceeds the maximum packet size, the packet is fragmented into a number of smaller packets that contain portions of the
contents of the original packet. This packet ow begins with an initial packet that contains all of the Layer 3 and Layer 4 header information
contained in the original packet, and is followed by a number of packets that contain only the Layer 3 header information.
This packet ow contains all of the information contained in the original packet distributed through the packet ow into packets that are
small enough to avoid the maximum packet size limit. This provides a particular problem for ACL processing.
If the ACL is ltering based on Layer 4 information, the non-initial packets within the fragmented packet ow will not match the Layer 4
information, even if the original packet that was fragmented would have matched the lter. Because of this ltering, packets that the ACL
was designed to lter for are not processed by the ACL.
The examples show both denying second and subsequent fragments, as well as permitting all packets on an interface. These ACLs deny all
second and subsequent fragments with destination IP 10.1.1.1, but permit the rst fragment and non-fragmented packets with destination IP
10.1.1.1. The second example shows ACLs which permits all packets — both fragmented and non-fragmented — with destination IP 10.1.1.1.
Deny second and subsequent fragments
OS10(config)# ip access-list ABC
OS10(conf-ipv4-acl)# deny ip any 10.1.1.1/32 fragments
OS10(conf-ipv4-acl)# permit ip any 10.1.1.1/32
Access Control Lists
377