ccna 3 commands pdf

ccna 3 commands pdf.As with typical firewall configurations, all incoming traffic is denied unless they are explicitly allowed (in this case, port 22 for SSH traffic), or unless they are associated with traffic originating from inside the network (in this case, HTTPS traffic). Any TCP traffic originating from outside the network with a source endpoint number of 443 and the control flag bit properly set is allowed in.4.1.4.4 Self-reversing ACLsSelf-reversing ACLs were introduced by CiscoIOS in 1996, one year after the TCPestablished option became available.Self-reversing ACLs are a second-generation solution for stateful firewalls. Self-inverting ACLs provide a more realistic form of session filtering than the TCPestablished option. Because packets need to match more filtering rules before they are allowed to pass, self-reversing ACLs are more difficult to spoof. For example, a self-reversing ACL not only checks the ACK and RST bits, but also the source and destination addresses and port numbers. In addition, session filters use temporary filters, which are removed after the session ends. This also adds a time limit to hacking attacks.The established keyword is only valid for TCP upper-layer protocols. For some other upper-layer protocols, such as UDP and ICMP, either all incoming traffic is allowed, or all allowable source, destination, host, and port address pairs are defined for each protocol.Self-reversing ACLs function by using temporary ACEs inserted into an extended ACL that is applied to the external interface of the perimeter router. After the session ends or the temporary entry expires, it is removed from the ACL configuration for the external interface. This reduces the risk of DoS attacks on the network. , , andTo implement this feature. the traffic needs to be checked as it leaves the network using an extended ACL that is named. ACLs can be applied to the inbound direction of an internal interface or the outbound direction of an external interface. The ACE uses the reflect parameter to check the traffic associated with the new session. Using these statements as a basis and using reflect, the connection to the ACE can be dynamically established to allow return traffic. Without the reflect statement, return traffic is discarded by default. For example, an administrator could set the ACL statement to check only HTTP connections, which would allow only temporary self-reversing ACEs to be created for HTTP trafficoWhen traffic leaves the network, a temporary entry will be added to the self-reflexive ACL if it matches an allowed statement with the reflect parameter. For each allowed self-reversal statement, the router creates a separate self-reversal ACL.A self-reversing ACE is a reverse entry where the source and destination information is reversed. For example, if a user Telnent to 209.165.200.5 on a workstation with an IP address of 192.168.1.3 and a source port number of 11000, a self-reversing ACE is created.R1(config-.ext-nacl)# permit host 209.165.200.5 eq 23 host 192,168.1.3 eq 110004.1 Access Control Lists 91