Vlan Maps; Handling Fragmented And Unfragmented Traffic - Cisco WS-C3020 Software Configuration Manual

Chapter 31 Configuring Network Security with ACLs
As with port ACLs, the switch examines ACLs associated with features configured on a given interface.
However, router ACLs are supported in both directions. As packets enter the switch on an interface,
ACLs associated with all inbound features configured on that interface are examined. After packets are
routed and before they are forwarded to the next hop, all ACLs associated with outbound features
configured on the egress interface are examined.
ACLs permit or deny packet forwarding based on how the packet matches the entries in the ACL, and
can be used to control access to a network or to part of a network. In
router input allow Host A to access the Human Resources network, but prevent Host B from accessing
the same network.

VLAN Maps

Use VLAN ACLs or VLAN maps to access-control all traffic. You can apply VLAN maps to all packets
that are routed into or out of a VLAN or are bridged within a VLAN in the stack or switch.
Use VLAN maps for security packet filtering. VLAN maps are not defined by direction (input or output).
You can configure VLAN maps to match Layer 3 addresses for IPv4 traffic.
All non-IP protocols are access-controlled through MAC addresses and Ethertype using MAC VLAN
maps. (IP traffic is not access controlled by MAC VLAN maps.) You can enforce VLAN maps only on
packets going through the switch; you cannot enforce VLAN maps on traffic between hosts on a hub or
on another switch connected to this switch.
With VLAN maps, forwarding of packets is permitted or denied, based on the action specified in the
map.
VLAN 10 from being forwarded. You can apply only one VLAN map to a VLAN.
Figure 31-2
Blade Server A
(VLAN 10)

Handling Fragmented and Unfragmented Traffic

IP packets can be fragmented as they cross the network. When this happens, only the fragment
containing the beginning of the packet contains the Layer 4 information, such as TCP or UDP port
numbers, ICMP type and code, and so on. All other fragments are missing this information.
Some ACEs do not check Layer 4 information and therefore can be applied to all packet fragments. ACEs
that do test Layer 4 information cannot be applied in the standard manner to most of the fragments in a
fragmented IP packet. When the fragment contains no Layer 4 information and the ACE tests some
Layer 4 information, the matching rules are modified:
•
OL-8915-03
Figure 31-2 shows how a VLAN map is applied to prevent a specific type of traffic from Host A in
Using VLAN Maps to Control Traffic
= VLAN map denying specific type
of traffic from Host A
= Packet
Permit ACEs that check the Layer 3 information in the fragment (including protocol type, such as
TCP, UDP, and so on) are considered to match the fragment regardless of what the missing Layer 4
information might have been.
Blade Server B
(VLAN 10)
Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide
Understanding ACLs
Figure 31-1, ACLs applied at the
31-5