Layer 4 Acl Rules Examples - Dell S4820T Configuration Manual

Dell(conf-ext-nacl)#permit ip any 10.1.1.1/32
Dell(conf-ext-nacl)

Layer 4 ACL Rules Examples

The following examples show the ACL commands for Layer 4 packet filtering.
Permit an ACL line with L3 information only, and the fragments keyword is present:
If a packet's L3 information matches the L3 information in the ACL line, the packet's FO is checked.
• If a packet's FO > 0, the packet is permitted.
• If a packet's FO = 0, the next ACL entry is processed.
Deny ACL line with L3 information only, and the fragments keyword is present:
If a packet's L3 information does match the L3 information in the ACL line, the packet's FO is checked.
• If a packet's FO > 0, the packet is denied.
• If a packet's FO = 0, the next ACL line is processed.
Example of Permitting All Packets from a Specified Host
In this first example, TCP packets from host 10.1.1.1 with TCP destination port equal to 24 are permitted.
All others are denied.
Dell(conf)#ip access-list extended ABC
Dell(conf-ext-nacl)#permit tcp host 10.1.1.1 any eq 24
Dell(conf-ext-nacl)#deny ip any any fragment
Dell(conf-ext-nacl)
Example of Permitting Only First Fragments and Non-Fragmented Packets from a Specified Host
In the following example, the TCP packets that are first fragments or non-fragmented from host 10.1.1.1
with TCP destination port equal to 24 are permitted. Additionally, all TCP non-first fragments from host
10.1.1.1 are permitted. All other IP packets that are non-first fragments are denied.
Dell(conf)#ip access-list extended ABC
Dell(conf-ext-nacl)#permit tcp host 10.1.1.1 any eq 24
Dell(conf-ext-nacl)#permit tcp host 10.1.1.1 any fragment
Dell(conf-ext-nacl)#deny ip any any fragment
Dell(conf-ext-nacl)
Example of Logging Denied Packets
To log all the packets denied and to override the implicit deny rule and the implicit permit rule for TCP/
UDP fragments, use a configuration similar to the following.
Dell(conf)#ip access-list extended ABC
Dell(conf-ext-nacl)#permit tcp any any fragment
Dell(conf-ext-nacl)#permit udp any any fragment
Dell(conf-ext-nacl)#deny ip any any log
Dell(conf-ext-nacl)
When configuring ACLs with the fragments keyword, be aware of the following.
When an ACL filters packets, it looks at the fragment offset (FO) to determine whether it is a fragment.
• FO = 0 means it is either the first fragment or the packet is a non-fragment.
• FO > 0 means it is dealing with the fragments of the original packet.
Access Control Lists (ACLs)
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