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White Paper. Filtering in Distributed Taps TM

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Filtering in Distributed Taps TM White Paper Copyright VSS Monitoring Inc. All rights reserved. By default, VSS Distributed Taps copy traffic received on the network input port(s) and forward
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Filtering in Distributed Taps TM White Paper Copyright VSS Monitoring Inc. All rights reserved. By default, VSS Distributed Taps copy traffic received on the network input port(s) and forward it to the monitor output port(s) as defined by the user through selective aggregation. By adding a filter (or filters) to that traffic, users can define which packets are passed to the monitor port(s) based on packet content. 1 Each filter is defined as a set of user-specified data values which will be compared to the data in network port received packets. These comparison values are specified for one or several standard packet fields (e.g. the MAC destination address field). Packets which contain the specified data values in the specified packet fields result in a filter match ( true ). Packets which do not contain the specified data values are a non-match ( false ). Each filter can be configured so that only matching packets are copied (in order to monitor only the specified type of packet), or so that all packets except matching packets are copied (in order to monitor all except the specified type of packet). Filtering & Latency VSS filtering is implemented in hardware, requiring no software or CPU processing. Thus, it operates in real time, introducing virtually no latency from the network inputs to the monitor outputs. Filter Condition Comparison Fields The following packet fields can be compared within any filter: MAC Source Address MAC Destination Address Etype VLAN ID Priority IEEE 802.1p/q Priority (if a tagged packet) IP Source Address IP (layer 3) source address (if an IP packet) IP Destination Address IP Version IPv4 Type of Service IPv6 Traffic Class IPv6 Flow IPv4 Protocol IPv6 Next Header TCP/UDP Source Port TCP/UDP Destination Port Custom Ethernet (IEEE Layer 2) source address. Ethernet (IEEE Layer 2) destination address Ethernet Type IEEE 802.1q VLAN ID (if a tagged packet) IEEE 802.1p/q Priority (if a tagged packet) IP (Layer 3) source address (if an IP packet) IP (Layer 3) destination address (if an IP packet) IP Protocol Version (if an IP packet) IP Type of Service field (if an IPv4 packet) IP Traffic Class field (if an IPv6 packet) IP Flow field (if an IPv6 packet) IP Protocol field (if an IPv4 packet) IP Next Header field (if an IPv6 packet) TCP or UDP Source Port field (if a TCP/UDP packet) TCP or UDP Destination Port field (if a TCP/UDP packet) User-specified A filter condition expression is specified with packet field names, and values to be compared against the packet field: packet field [=] value Multiple such comparisons may be joined using the keywords and or or. Compound expressions (using and / or ) are evaluated left-to-right, but an explicit evaluation order may be specified using ( and ). Examples: mac source = 00AA ethernet source 00AA or ethernet destination 00AA (destination ip address or source ip address ) and ip prot=6 (1) Filtering applies only to the monitor port. The data passing from one network port to the other (when configured as inline tap ports) is always unaffected and is passed-through completely transparently. 2 Offset Filters There are two types of offset (custom) filters depending on the specific product platform. Each allows the user to create a byte filter window, beginning at the MAC, IP, TCP, or UDP header for comparison with all packets that pass through the filter. Within the window the user specifies an offset from the beginning of the window and the desired hexadecimal data pattern to be compared to received packets. For example, offset 6 (MAC header plus 6) against the pattern 00dd As another example, ip offset 15 = 02 specifies a comparison of the last byte of the IPv4 Source field (IP header plus 15 bytes) against the single-byte pattern 02. Masking A command is a qualifier for the data pattern entered in bits. This will cause the value specified to be AND ed with the packet data. The result will be compared with the comparison data entered and if this data equates, the filter will see a match. This ing feature allows the user to isolate single bits or groups of bits as desired (for filtering on partial bytes). For example, to filter only packets where the low-order bit of the IPv4 Source address is a 1, specify ip offset 15 = Packet Fields The following packet field names can be used in a condition expression : Packet Fields Alternate Forms v2 v3 Comparison Value mac source mac destination mac source address, ethernet source [address], source mac ethernet [address] mac ethernet dest[ination] [address], dest[ination] mac ethernet [ad dress] 48-bit Ethernet address, entered as 12 hexadecimal digits, with optional embedded space, - or : charac ters for readability, e.g.: 00dd [same as mac source] etype [mac ethernet] etype 16-bit hexadecimal value (four vlan priority ip source ip destination [mac ethernet] [outer] vlanid, [mac ethernet] [outer] vid [mac ethernet] [outer] pri, [mac ethernet] [outer] qos ip src [address], source src ip [address] ip dest [address], dest[ination] ip [address] Range Range optional: optional: ip version ip ver 4 or 6 hexadecimal digits) Decimal value in the range Decimal value in the range 0-7 To specify an IPv4 address enter the address using standard dotted-decimal notation, e.g.: A range of IPv4 addresses may also be specified by en tering two dotted-decimal IPv4 addresses separated by -, e.g.: (a received packet with an IP destination address anywhere within the specified range is considered a pattern match). To specify an IPv6 address, enter the address as an IPv6 128-bit address using hexadecimal digits. [same as ip source] continued on next page 3 Packet Fields Alternate Forms v2 v3 Comparison Value ip version ip ver 4 or 6 ip tos ip tos 8-bit value specified as two hexadecimal digits ip protocol ip prot 20-bit value specified as 5 hexadecimal digits ip flow ip flow Decimal value tcp source tcp destination [tcp udp] src source port, source src [tcp udp] port [tcp udp] dest[ination] port, dest[ination] [tcp udp] port offset nnn [mac ip tcp udp] offset nnn optional: Range Range Decimal value , or a range of value separated by a - character, e.g.: ; or even or odd. Range Range [same as tcp source] optional: *Items noted above with Range may optionally be specified with a range of values, e.g. value1-value2. The number of packet fields per filter and the number of values compared against each field per expression depend on the specific model. For the majority of VSS Distributed Taps with filtering, there is no per-filter limitation. 2 Filter Examples The following filter will match only HTTP request packets: ip version 4 and ip protocol 6 and tcp destination port 8 The following filter will match only FTP packets (FTP Control or FTP Data): ip version 4 and ip protocol 6 and tcp destination port To monitor all traffic to or from a particular node/pc, the node s Ethernet/MAC address (00AA in this example) can be used in a filter expression such as: mac source 00AA or mac destination 00AA Alternatively, the node s IP address could be used ( in this example): ip source or ip destination To monitor one particular connection/conversation/session between two nodes ( and in this example) use an expression like this: (ip source and ip destination ) or (ip source and ip source ) To monitor one particular TCP/IP protocol (in this example HTTP) use an expression such as this, which filters IP protocol 6 (TCP) and IP port 80 (HTTP): ip protocol 6 and (tcp source port 80 or tcp destination port 80) Or, in a combination of the above, to monitor a particular protocol (e.g. HTTP) from one particular node (e.g ): (ip source or ip destination )and ip protocol 6 and (tcp source port 80 or tcp destination port 80) (2) In this case, the per-filter packet field limitation is equal to the total packet field limit of the tap. 4 Creating and Applying Filters with a Web Browser The Filter Library User-defined filters are stored within a Filter Library. A collection of many filters can be predefined by the user, and then specific filters called upon as the need arises. Once a filter has been defined in the library, that filter can then be used repeatedly on multiple ports at any time without the need to re-define the entire filter each time. Filters are identified by user-defined symbolic names. Creating Filters Selecting the Filter Library link on the main page will bring up a screen which allows the configuration of all monitor filters. The currently-defined filters (if any) will be shown on the screen. The top-left of the page displays a list of the currentlydefined filters. To view an existing filter, simply click once on the name of the filter. To add a new filter to the Filter Library, click once on + Add new filter. In the entry box labeled Filter Name type the desired symbolic name for the new filter; enter the new filter specifications in the fields below, then click the Save Filter button to add the new filter to the library. To change an existing filter, first select the filter by clicking once on its name, and then enter the new filter specifications in the fields below; finally click the Save Filter button. Note that changing an existing filter will automatically update the filter on all ports to which the filter has already been applied. To remove an existing filter, first select the filter by clicking once on its name, and then click the Delete Filter button. A pop-up dialog box will ask for confirmation before deleting the filter. Below the filter list is a text input field showing the text of the selected filter conditional expression. You can enter a conditional expression directly into the input field if desired. Alternatively, below the conditional expression are three tabs labeled Quick, Detailed, and Advanced. Each of these represents a different way to configure the filters, although all result in a single conditional expression which becomes a part of the Filter Library. In most cases the Quick tab is the easiest way to configure filters, and is recommended and appropriate for most filtering situations. This tab allows easy specification of MAC address, IP address, and/or protocol. The Detailed tab allows more advanced configuration of the individual conditions. This tab allows configuration of parameters not available under the Quick tab, including VLAN ID and IP Type of Service (TOS). The Detailed tab contains input fields to configure all of the possible fields for which to compare against received packets. To change a setting, simply click within the field and enter the desired value. To remove (disable) a setting (to make it don t care or any value ), simply click within the field and delete the field value (making it empty or blank). Fields for which settings have been made (non-blank fields) will be highlighted on the screen for emphasis; blank ( don t care ) fields are not highlighted. 5 The Advanced tab facilitates direct entry of the text of a conditional expression. Directly entering the conditional expression allows for complex combination of ANDing and ORing which would not be available from the other tabs. This tab displays a help screen showing the available packet fields and their associated expression keywords. To directly enter an expression, click in the Condition input box and type the desired expression. Be aware that all three of the tabs create a single conditional expression (each is just a different method of creating an expression). Entering something on one tab will create new text (visible in the Condition text box) that will overwrite anything that might have been previously entered using a different tab., i.e. if you create a filter in the Advanced tab, the filter settings will be overwritten if you then use the Quick tab to modify these settings. Applying Filters After the desired filters have been added to the Filter Library, it is then possible to apply the filters to specific network ports. The method of applying filters varies slightly for each available platform type; however, in all cases, the application of filters is done in conjunction with mapping network inputs to monitor outputs (selective aggregation), as well as other traffic distribution options such as load balancing. Frequently Asked Questions How do I specify an IP range filter? For the v2 platform, an IP range filter is specified by using a hyphen between the start and end range IP address: In the v3 platform, an IP range filter is specified using a : The above expression would filter all IP addresses including and between and I only want to see RTP traffic. How do I filter for this? The easiest method to filter RTP would be to find out the UDP port range used by your particular network for RTP packets. This can vary, but typically, the following port numbers apply: TCP/UDP (RTCP = RTP+1) Another method for filtering RTP would be to create a custom filter that defines RTP traffic by the type of payload associated with that packet. For example, to filter RTP with payload type 20: udp offset f How do I create a filter for VoIP traffic? VoIP traffic is application dependent so methods of filtering this traffic will vary. Typically, VoIP traffic would be defined by TCP/UDP port and/or RTP payload type (custom filter). How do I apply a filter to GTP tunneled traffic? The GTP Tunneling Protocol is encapsulated within UDP, using the fixed UDP port number The GTP header follows the UDP header, and following the GTP header is the user s original IP datagram. 6 As GTP headers are variable in length, it is not possible to create any single filter which under all conditions can examine the contents of the encapsulated user IP datagram. In order to accomplish this, the user needs to know the length of the GTP header being used in his/her application, and adjust the filter accordingly. The below example assumes the GTP header is 12 bytes in length. The following expression will filter just GTP packets (IP protocol = U17 & UDP dest port = 2152): ip protocol 17 and udp destination port 2152 The GTP header begins at offset 8 from the start of the UDP header (since the UDP header is 8 bytes long) so: udp offset 8 will point to the GTP header. If we assume a 12-byte GTP header then: udp offset 20 will point to the start of the user s encapsulated IP datagram. The IP source address is found at offset 12 within an IP header. Therefore the following will point to the IP source address within the GTP user s encapsulated datagram: udp offset 36 Combine the above as desired to create a complete filter expression, e.g. to filter user s IP source address (hex ): ip protocol 17 and udp destination port 2152 and udp offset or to filter user s IP destination address (hex ): ip protocol 17 and udp destination port 2152 and udp offset An optional parameter can also be specified following the offset custom packet field, to include/exclude individual bits/nibbles/bytes within the field. So, this could be used if it was desired to filter on a particular user s encapsulated subnet, e.g. assuming a subnet of then user subnet 1.3.6/ could be filtered with: ip protocol 17 and udp destination port 2152 and udp offset fffffc If desired, the above could be made more specific/complex to filter, for example, traffic only to a specific GTP destination, e.g : ip destination and ip protocol 17 and udp destination port 2152 and udp offset Note: All of the above-defined filters may (depending on the network traffic) result in some additional packets passing the filter (which could simply be ignored in the monitor output stream), e.g., if there is any other kind of traffic carried on UDP port VSS Monitoring, Inc. is the world s leading innovator of Distributed Traffic Capture Systems and network taps, focused on meeting the rapidly evolving requirements of security and performance conscious network professionals. Distributed Traffic Capture Systems herald a new architecture of network monitoring, one which fundamentally improves its capability and price-performance. VSS, Distributed Traffic Capture System, vassure, LinkSafe, 12x4 Distributed Tap and 8x8 Distributed Tap are trademarks or registered trademarks of VSS Monitoring, Inc. in the United States and other countries. Any other trademarks contained herein are the property of their respective owners.
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