HP Cisco Catalyst Blade Switch 3020 Cisco Catalyst Blade Switch 3020 for HP So - Page 492

VLAN Maps, Handling Fragmented and Unfragmented Traffic

Page 492 highlights

Understanding ACLs Chapter 26 Configuring Network Security with ACLs Note You cannot apply more than one IP access list and one MAC access list to a Layer 2 interface. If an IP access list or MAC access list is already configured on a Layer 2 interface and you apply a new IP access list or MAC access list to the interface, the new ACL replaces the previously configured one. VLAN Maps You use VLAN ACLs or VLAN maps to filter traffic between devices in the same VLAN. When a VLAN map is applied to a VLAN, all packets being forwarded in the VLAN are checked against the VLAN map. 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. Figure 26-2 shows how a VLAN map is applied to prevent a specific type of traffic from Host A in VLAN 10 from being forwarded. You can apply only one VLAN map to a VLAN. Figure 26-2 Using VLAN Maps to Control Traffic Blade Server A (VLAN 10) Blade Server B (VLAN 10) 101353 = VLAN map denying specific type of traffic from Host A = Packet 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: • 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. • Deny ACEs that check Layer 4 information never match a fragment unless the fragment contains Layer 4 information. 26-4 Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide OL-8915-01

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26-4
Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide
OL-8915-01
Chapter 26
Configuring Network Security with ACLs
Understanding ACLs
Note
You cannot apply more than one IP access list and one MAC access list to a Layer 2 interface. If an IP
access list or MAC access list is already configured on a Layer 2 interface and you apply a new IP access
list or MAC access list to the interface, the new ACL replaces the previously configured one.
VLAN Maps
You use VLAN ACLs or VLAN maps to filter traffic between devices in the same VLAN. When a VLAN
map is applied to a VLAN, all packets being forwarded in the VLAN are checked against the VLAN map.
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.
Figure 26-2
shows how a VLAN map is applied to prevent a specific type of traffic from Host A in
VLAN 10 from being forwarded. You can apply only one VLAN map to a VLAN.
Figure 26-2
Using VLAN Maps to Control Traffic
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:
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.
Deny ACEs that check Layer 4 information never match a fragment unless the fragment contains
Layer 4 information.
Blade Server B
(VLAN 10)
Blade Server A
(VLAN 10)
101353
=
VLAN map denying specific type
of traffic from Host A
=
Packet