Troubleshooting

Unusual Network Activity

common mistake is to either not explicitly permit the switch’s IP address as a DA or to use a wildcard ACL mask in a deny statement that happens to include the switch’s IP address. For an example of this problem, refer to the section titled “General ACL Operating Notes” in the “Access Control Lists (ACLs)” chapter of the latest Access Security Guide for your switch.

Routing Through a Gateway on the Switch Fails

Configuring a “deny” ACE that includes a gateway address can block traffic attempting to use the gateway as a next-hop.

Remote Gateway Case. For example, configuring ACL “101” (below) and applying it outbound on VLAN 1 in Figure C-4includes the router gateway (10.0.8.1) needed by devices on other networks. This can prevent the switch from sending ARP and other routing messages to the gateway router to support traffic from authorized remote networks.

In Figure C-4,this ACE denies access to the 10 Net’s 10.0.8.1 router gateway needed by the 20 Net.

(Subnet mask is 255.255.255.0.)

Figure C-3. Example of ACE Blocking an Entire Subnet
C-12