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This chapter describes how to use filters to improve the performance of your bridge.
Here's what you'll find in this chapter:
If your bridge is connected to an infrastructure with a large amount of multi-protocol traffic, you may be able to reduce the amount of radio traffic by blocking out (filtering) unneeded addresses or protocols. This filtering is especially important for battery-operated radio nodes that might otherwise have to waste considerable battery power receiving irrelevant multicast messages.
Use the Filter menu to control packet filtering.
Navigation: Main > Filter
The Multicast menu controls the filtering of multicasts based on the actual multicast address.
Navigation: Main > Filter > Multicast
The Default option controls the filtering of multicasts whose address is not in the table. You may pick one of the following actions:
Discard: multicasts with no table entries are not forwarded out of the radio network.
Forward: multicasts with no table entries are forwarded out of the radio network.
The Show option displays the Multicast Filters screen. The filters are stored in the association table. The display of the multicast filters follows the format of the normal association display. At the end of each line the filter action for each address is displayed.
The multicast filters can also be displayed by using the menu sequence Main > Association > Display. See Chapter 8, "Using the Association Table."
The Add option adds a multicast filter if there are special multicast addresses you want to filter differently than the default. You are first prompted for the address and then for an action to be applied to this address only.
The Remove option removes one or all of the non-default filters. The action for the removed entries reverts to the default action.
The Node option controls the forwarding of packets based on the source node addresses. Type specific node filters by specifying the 6-byte infrastructure address of the node or by specifying its IP address. If the IP address is used, the bridge determines the infrastructure address associated with the IP address and uses it for the actual filtering. You can filter packets based on the source address in the received packet.
Navigation: Main > Filter > Node
The Ethdst default applies to those packets whose addresses do not have entries in the filter table. Options are forward or discard. Source address filtering is forward by default.
Use the Display option to view the table of controlled addresses. The filters are stored in the association table so that they can be accessed quickly. The display of the filters follows the format of the normal association display. At the end of each line the filter action for each address is displayed.
The node filters can also be displayed by using the menu sequence Main > Association > Display. See Chapter 8, "Setting Up the Association Table."
When a node address filter is entered by IP address, the bridge first determines the infrastructure address associated with this IP address. The actual filtering is done based on the infrastructure address.
Use the Add option to add filters for specific addresses to the filter table. You will be prompted for the infrastructure address or IP address of the node to which the filter applies. You will then be asked for the filter action to be applied to this address, which is either filter or discard.
To remove one or all specific node filters use the Remove option. You can enter the keyword all, a single node's infrastructure address, or a single node's IP address. Once removed, the filter action for the removed addresses reverts to the default value.
Protocol filtering bases the filtering decision on the type of protocol used to encapsulate the data in the packet. This type of filtering can have the most value in almost all situations and is the preferred method of filtering. With this type of filtering you can set the bridge to only forward those protocols that are being used by the remote nodes. Selecting protocols is easier than setting up filters based on addresses. The bridge can be set up to monitor and record the list of protocols currently being forwarded over the radio. It records the protocols found, how many packets are encountered, and whether the packet comes from the LAN or the radio.
To set up the protocol filters, start the monitor and let it run for a while under normal use. Add filters by selecting the protocols from the monitor list. There is a default action for those protocols not in the list of explicitly filtered protocols. If you know exactly which protocols are going to be used by the radio nodes, set the default action to discard; then add filters to forward only those protocols that will be used. If you are not sure of all the protocols that will be used but you know that there are certain protocols you will not use, you should set the default action to forward; then add filters to discard only those protocols you will not use. For filtering purposes, the bridge assumes that the data portion of the packets is in one of two forms:
You can set up filters based on either a protocol identifier or a DSAP/ SSAP combination. If the filter is based on SAPs and the control field has a value of 3, the packet can also be filtered based on the OUI and LLC protocol fields. Both types of filters can also use a variable length bit mask of the packet contents to further specify which packets should be filtered.
Navigation: Main > Filter > Protocols
The Default action is used for a packet whose protocol does not match any entry found in the table. It may be set to:
Use the Unicast option to filter unicast packets. By default, the bridge applies the protocol filters only to multicast packets. If a packet is directed to a radio node, it is likely the protocol in the packet is being used by the radio node.
Use the Display option to view the list of protocol filters you have added.
Use the Add option to add a protocol filter and specify the type of action required. There are several ways to add a filter:
To add a predefined filter:
Step 2 Type one of the predefined strings: inet, novell, netbios, txp, ip_subprotocol, ip_port, or ip_address and press Enter.
Step 3 You are then prompted for the action to take when the protocol is encountered. Type discard, forward, high_priority or log, and press Enter.
To add a filter using the monitor:
If protocol monitoring is enabled, when you select add, the current monitor table is displayed. Follow these steps to select a monitored protocol:
a. If the monitored protocol was unrecognized and was not given a name, you are then prompted to assign a name.
Step 2 You are then prompted for the action to take when the protocol is encountered. Type discard, forward, high_priority or log and press Enter.
To add a filter manually:
Follow these steps to start adding a filter manually:
Step 2 You are then prompted for the action to take when the protocol is encountered. Type discard, forward, high_priority or log and press Enter.
Step 3 Then the following message appears:
Enter one of [protocol, snap+protocol, llc]:
Step 4 Choose whether the protocol is defined by an Ethernet or SNAP+protocol identifier or by an LLC header.
If you type protocol:
a. The following prompt appears:
Type a value in hex from 200h to ffffh:
b. Then the following prompt appears:
Type one of [a mask start position, none]:
c. Then the following prompt appears:
Type a hex value of 1 to 30 characters:
d. Then the following prompt appears:
Type a hex don't care mask of 1 to 6 characters:
Type one of [a mask start position, none]: 15 Type a hex value of 1 to 30 characters: 4128 Type a hex don't care mask of 1 to 4 characters: 8080
If you type llc:
a. The following prompt appears:
Type a value in hex of ffffh or less:
b. Then the following prompt appears:
Type one of [a OUI value in hex of ffffffh or less, any]:
c. Type the applicable OUI value or any and press Enter.
Type one of [a LLC protocol value in hex of ffffh or less, any]:
d. You are then prompted for a mask description as described in the protocol section above.
Use the Remove option to remove a protocol filter entry. You may either remove all filters by typing all or a single entry by typing the number assigned to the filter and shown at the start of the line in the filter display.
Use the Length option to display the contents of packets being forwarded to the radio. Use this option to setup the filter mask values. If you add a protocol filter whose action is log, each time the filter matches, the contents of the data portion of the packet (after the MAC header) will be displayed on the console (in hexadecimal) for a length in bytes determined by the value of this option. The contents of the data portion displayed in the information log will consist of:
The following is an example of a protocol filter log entry:
p2: 01 e0 ff ff 01 eo 00 04 00 00 01 65 ff ff ff ff ff ff 04 52 00 00
The bridge allows you to create and display a list of the protocols being forwarded by the bridge. This allows you to test if packets that contain data for unused protocols are being forwarded to the radio nodes. After it is enabled by the Monitor option, the bridge begins to examine the protocol used in each packet forwarded. If the protocol is not already in the list, an entry is created. Otherwise, the packet count for the given protocol is incremented.
The Show option displays the list of currently forwarded protocols.
Use the Clear option to clear the list of found protocols either with the Clear command or by typing a capital C at the re-display prompt of the Show command.
Use the Direction option to control the direction a packet is traveling before it is affected by the filters. Select one of the following options:
Posted: Wed Aug 9 15:01:02 PDT 2000
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