x900-24 series Manuals

Creating dedicated hardware filters
Configuring Layer 4 source and destination port number masks
A common filtering requirement is the ability to filter on a range of TCP or UDP port 
numbers. For example, we often want to be able to allow through all packets with a TCP 
destination port greater than 1024, as such packets are deemed to be replies coming back to 
sessions initiated from the other side of the switch.The l4smask and l4dmask parameters 
make it possible for a single classifier to match a whole range of port numbers.
These parameters take on HEX values, and are used in conjunction with the parameters 
tcpsporttcpdportudpsport, and udpdport. A range of port numbers matches the 
classifier if performing a logical AND with the mask would give the same result as performing 
a logical AND with the value specified in the corresponding sport or dport parameter.
Of course, this is not quite so convenient as being able to simply specify a range of decimal 
numbers. Often it can require multiple port/mask combinations to cover a particular range of 
This maths of all this is described in detail in Appendix A of this How To Note—see page 13.
The default value of each mask is FFFF. This means that if you specify a port number 
without specifying a mask, then the classifier matches only that one value of the port 
number. This is the same as specifying a port number and a mask of FFFF.
Configuring “inner” parameters for nested VLANs
The tpid, innertpid, innervlanid, and innervlanpriority parameters all apply to nested 
VLAN configuration. In this situation, the packets arriving at the core-facing port can have 
two VLAN tags configured on them.
The  tpid parameter matches on the first Tag Protocol Identifier field in the packet.
The innertpid parameter matches on the TPID in the second 802.1Q tag in the packet.
The innervlanid parameter matches on the tunnelled VLAN ID in the second 802.1Q tag 
in the packet.
The innervlanpriority parameter matches on the 802.1P field in the second tag in the 
The following table shows where in the packet the inner and outer tags will be matched. 
Outer VLAN parameters
Inner VLAN parameters
Customer port
1st tag
Core port
1st tag
2nd tag
Nested VLANs disabled
1st tag
2nd tag
Some important points to keep in mind while configuring the “inner” parameters are:
When packets arrive at a customer port of a nested VLAN, the parameter vlan will match 
the VID of the nested VLAN that the port is a member of, which is just how this parameter 
normally operates.
Page 4 | AlliedWare™ OS How To Note: Hardware Filters

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