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Dell EMC SmartFabric OS10 User Guide Release 10.5.1

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L3 ACL rules

Use ACL commands for L3 packet filtering. TCP packets from host 10.1.1.1 with the TCP destination port equal to 24 are permitted, and all others are denied.

TCP packets that are first fragments or non-fragmented from host 10.1.1.1 with the TCP destination port equal to 24 are permitted, and all TCP non-first fragments from host 10.1.1.1 are permitted. All other IP packets that are non-first fragments are denied.

Permit ACL with L3 information only

If a packet’s L3 information matches the information in the ACL, the packet's fragment offset (FO) is checked:
  • If a packet's FO > 0, the packet is permitted
  • If a packet's FO = 0, the next ACL entry processes

Deny ACL with L3 information only

If a packet's L3 information does not match the L3 information in the ACL, 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 processes

Permit all packets from host

OS10(config)# ip access-list ABC
OS10(conf-ipv4-acl)# permit tcp host 10.1.1.1 any eq 24
OS10(conf-ipv4-acl)# deny ip any any fragment

Permit only first fragments and non-fragmented packets from host

OS10(config)# ip access-list ABC
OS10(conf-ipv4-acl)# permit tcp host 10.1.1.1 any eq 24
OS10(conf-ipv4-acl)# permit tcp host 10.1.1.1 any fragment
OS10(conf-ipv4-acl)# deny ip any any fragment
To log all packets denied and to override the implicit deny rule and the implicit permit rule for TCP/ UDP fragments, use a similar configuration. When an ACL filters packets, it looks at the 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 the fragments of the original packet

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