object time-exceeded icmp-object echo-reply access-list Inbound permit icmp any any object-group ICMP-Types access-group Inbound in interface outside Allowing MTU Path Discovery Packets MTU path discovery allows devices on remote networks to inform you of MTU limi- tations. To enable this, you must allow two more ICMP types: source-quench and parameter-problem. You can allow them on Cisco routers and PIX firewalls as follows: Cisco routers: access-list 101 remark [< Allows PING and Traceroute >] access-list 101 permit icmp any any unreachable access-list 101 permit icmp any any time-exceeded access-list 101 permit icmp any any echo-reply access-list 101 permit icmp any any parameter-problem access-list 101 permit icmp any any source-quench interface Ethernet1 ip access-group 101 in Firewalls: object-group icmp-type ICMP-Types description [< Allowed ICMP Types > ] Designing Access Lists icmp-object unreachable icmp-object time-exceeded icmp-object echo-reply icmp-object source-quench icmp-object parameter-problem access-list Inbound permit icmp any any object-group ICMP-Types access-group Inbound in interface outside ACLs in Multilayer Switches Multilayer switches, by nature of their design, allow for some security features not available on layer-2 switches or routers. The 3750 switch supports IP ACLs and Ethernet (MAC) ACLs. Access lists on a 3750 switch can be applied in the following ways: Port ACLs Port ACLs are applied to layer-2 interfaces on the switch. They cannot be applied to EtherChannels, SVIs, or any other virtual interfaces. Port ACLs can be applied to trunk interfaces, in which case they will filter every VLAN in the trunk. Standard IP, extended IP, or MAC ACLs can be assigned as port ACLs. Port ACLs can be applied only in the inbound direction. Router ACLs Router ACLs are applied to layer-3 interfaces on the switch. SVIs, layer-3 physical interfaces (configured with no switchport, for example), and layer-3 EtherChannels can have router ACLs applied to them. Standard IP and extended IP ACLs can be a