C-12
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-4 includes 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.
Figure C-3. Example of ACE Blocking an Entire Subnet
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.)
3500-5400-6200-8200-MCG-Jan08-K_13_01.book Page 12 Monday, January 28, 2008 10:04 AM