Dell S4820T, Configuration Manual

Page: 134 / 1178

In cases such as these, where class-maps with overlapping ACL rules are applied to different queues, use
the
order
keyword to specify the order in which you want to apply ACL rules. The order can range from
0 to 254. Dell Networking OS writes to the CAM ACL rules with lower-order numbers (order numbers
closer to 0) before rules with higher-order numbers so that packets are matched as you intended. By
default, all ACL rules have an order of
255 .
Example of the
order
Keyword to Determine ACL Sequence
Dell(conf)#ip access-list standard acl1
Dell(config-std-nacl)#permit 20.0.0.0/8
Dell(config-std-nacl)#exit
Dell(conf)#ip access-list standard acl2
Dell(config-std-nacl)#permit 20.1.1.0/24 order 0
Dell(config-std-nacl)#exit
Dell(conf)#class-map match-all cmap1
Dell(conf-class-map)#match ip access-group acl1
Dell(conf-class-map)#exit
Dell(conf)#class-map match-all cmap2
Dell(conf-class-map)#match ip access-group acl2
Dell(conf-class-map)#exit
Dell(conf)#policy-map-input pmap
Dell(conf-policy-map-in)#service-queue 7 class-map cmap1
Dell(conf-policy-map-in)#service-queue 4 class-map cmap2
Dell(conf-policy-map-in)#exit
Dell(conf)#interface te 10/1
Dell(conf-if-te-10/1)#service-policy input pmap
IP Fragment Handling
Dell Networking OS supports a configurable option to explicitly deny IP fragmented packets, particularly
second and subsequent packets.
It extends the existing ACL command syntax with the
fragments
keyword for all Layer 3 rules applicable
to all Layer protocols (permit/deny ip/tcp/udp/icmp).
• Both standard and extended ACLs support IP fragments.
• Second and subsequent fragments are allowed because a Layer 4 rule cannot be applied to these
fragments. If the packet is to be denied eventually, the first fragment would be denied and hence the
packet as a whole cannot be reassembled.
• Implementing the required rules uses a significant number of CAM entries per TCP/UDP entry.
• For IP ACL, Dell Networking OS always applies implicit deny. You do not have to configure it.
• For IP ACL, Dell Networking OS applies implicit permit for second and subsequent fragment just prior
to the implicit deny.
• If you configure an explicit deny, the second and subsequent fragments do not hit the implicit permit
rule for fragments.
• Loopback interfaces do not support ACLs using the
IP fragment
option. If you configure an ACL
with the
fragments
option and apply it to a Loopback interface, the command is accepted but the
ACL entries are not actually installed the offending rule in CAM.
IP Fragments ACL Examples
The following examples show how you can use ACL commands with the
fragment
keyword to filter
fragmented packets.
134
Access Control Lists (ACLs)