Dell PowerSwitch S4820T 9.50.1 Configuration Guide for the S4820T System - Page 121

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 10/0 Dell(conf-if-te-10/0)#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. Example of Permitting All Packets on an Interface The following configuration permits all packets (both fragmented and non-fragmented) with destination IP 10.1.1.1. The second rule does not get hit at all. Dell(conf)#ip access-list extended ABC Dell(conf-ext-nacl)#permit ip any 10.1.1.1/32FTOS(conf-ext-nacl)#deny ip any Access Control Lists (ACLs) 121