MATE will make a Pdu for each different proto field of Proto type present in the frame. MATE will fetch from the field’s tree those fields that are defined in the Section 12.8.1, “Pdsu’s configuration actions” declaration whose initial offset in the frame is within the boundaries of the current Proto and those of the given Transport and Payload statements.

Pdu dns_pdu Proto dns Transport ip {
    Extract addr From ip.addr;
    Extract dns_id From dns.id;
    Extract dns_resp From dns.flags.response;
};

MATE will make a Pdu for each different proto field of Proto type present in the frame. MATE will fetch from the field’s tree those fields that are defined in the Section 12.8.1, “Pdsu’s configuration actions” AVPL whose initial offset in the frame is within the boundaries of the current Proto and those of the various assigned Transports.

Once MATE has found a Proto field for which to create a Pdu from the frame it will move backwards in the frame looking for the respective Transport fields. After that it will create AVPs named as each of those given in the rest of the AVPL for every instance of the fields declared as its values.

Sometimes we need information from more than one Transport protocol. In that case MATE will check the frame looking backwards to look for the various Transport protocols in the given stack. MATE will choose only the closest transport boundary per "protocol" in the frame.

This way we’ll have all Pdus for every Proto that appears in a frame match its relative transports.

Pdu isup_pdu Proto isup Transport mtp3/ip {
        Extract m3pc From mtp3.dpc;
        Extract m3pc From mtp3.opc;
        Extract cic From isup.cic;
        Extract addr From ip.addr;
        Extract isup_msg From isup.message_type;
};

This allows to assign the right Transport to the Pdu avoiding duplicate transport protocol entries (in case of tunneled ip over ip for example).

Pdu ftp_pdu Proto ftp Transport tcp/ip {
        Extract addr From ip.addr;
        Extract port From tcp.port;
        Extract ftp_cmd From ftp.command;
};

Other than the mandatory Transport there is also an optional Payload statement, which works pretty much as Transport but refers to elements after the Proto's range. It is useful in those cases where the payload protocol might not appear in a Pdu but nevertheless the Pdu belongs to the same category.

Pdu mmse_over_http_pdu Proto http Transport tcp/ip {

        Payload mmse;

        Extract addr From ip.addr;
        Extract port From tcp.port;
        Extract method From http.request.method;
        Extract content From http.content_type;
        Extract http_rq From http.request;
        Extract resp From http.response.code;
        Extract host From http.host;
        Extract trx From mmse.transaction_id;
        Extract msg_type From mmse.message_type;
        Extract notify_status From mmse.status;
        Extract send_status From mmse.response_status;
};

There might be cases in which we won’t want MATE to create a PDU unless some of its extracted attributes meet or do not meet some criteria. For that we use the Criteria statements of the Pdu declarations.

Pdu isup_pdu Proto isup Transport mtp3/ip {
    ...

   // MATE will create isup_pdu PDUs only when there is not a point code '1234'
   Criteria Reject Strict (m3pc=1234);
};

Pdu ftp_pdu Proto ftp Transport tcp/ip {
    ...

    // MATE will create ftp_pdu PDUs only when they go to port 21 of our ftp_server
    Criteria Accept Strict (addr=10.10.10.10, port=21);
};

The Criteria statement is given an action (Accept or Reject), a match mode (Strict, Loose or Every) and an AVPL against which to match the currently extracted one.

Once the fields have been extracted into the Pdu’s AVPL, MATE will apply any declared transformation to it. The way transforms are applied and how they work is described later on. However it’s useful to know that once the AVPL for the Pdu is created, it may be transformed before being analyzed. That way we can massage the data to simplify the analysis.

Every successfully created Pdu will add a MATE tree to the frame dissection. If the Pdu is not related to any Gop, the tree for the Pdu will contain just the Pdu’s info, if it is assigned to a Gop, the tree will also contain the Gop items, and the same applies for the Gog level.

mate dns_pdu:1
    dns_pdu: 1
        dns_pdu time: 3.750000
        dns_pdu Attributes
            dns_resp: 0
            dns_id: 36012
            addr: 10.194.4.11
            addr: 10.194.24.35

The Pdu’s tree contains some filterable fields

Given a Pdu, the first thing MATE will do is to check if there is any Gop declaration in the configuration for the given Pdu type. If so, it will use its Match AVPL to match it against the Pdu’s AVPL; if they don’t match, the analysis phase is done. If there is a match, the AVPL is the Gop’s candidate key which will be used to search the Gop’s index for the Gop to which to assign the current PDU. If there is no such Gop and this Pdu does not match the Start criteria of a Gop declaration for the Pdu type, the Pdu will remain unassigned and only the analysis phase will be done.

Gop ftp_ses On ftp_pdu Match (addr, addr, port, port);
Gop dns_req On dns_pdu Match (addr, addr, dns_id);
Gop isup_leg On isup_pdu Match (m3pc, m3pc, cic);

If there was a match, the candidate key will be used to search the Gop’s index to see if there is already a Gop matching the Gop’s key the same way. If there is such a match in the Gops collection, and the PDU doesn’t match the Start AVPL for its kind, the PDU will be assigned to the matching Gop. If it is a Start match, MATE will check whether or not that Gop has been already stopped. If the Gop has been stopped, a new Gop will be created and will replace the old one in the Gop’s index.

Gop ftp_ses On ftp_pdu Match (addr, addr, port, port) {
    Start (ftp_cmd=USER);
};

Gop dns_req On dns_pdu Match (addr, addr, dns_id) {
    Start (dns_resp=0);
};

Gop isup_leg On isup_pdu Match (m3pc, m3pc, cic) {
    Start (isup_msg=1);
};

If no Start is given for a Gop, a Pdu whose AVPL matches an existing Gog’s key will act as the start of a Gop.

Once we know a Gop exists and the Pdu has been assigned to it, MATE will copy into the Gop’s AVPL all the attributes matching the key plus any AVPs of the Pdu’s AVPL matching the Extra AVPL.

Gop ftp_ses On ftp_pdu Match (addr, addr, port, port) {
    Start (ftp_cmd=USER);
    Extra (pasv_prt, pasv_addr);
};

Gop isup_leg On isup_pdu Match (m3pc, m3pc, cic) {
    Start (isup_msg=1);
    Extra (calling, called);
};

Once the Pdu has been assigned to the Gop, MATE will check whether or not the Pdu matches the Stop, if it happens, MATE will mark the Gop as stopped. Even after stopped, a Gop may get assigned new Pdus matching its key, unless such Pdu matches Start. If it does, MATE will instead create a new Gop starting with that Pdu.

Gop ftp_ses On ftp_pdu Match (addr, addr, port, port) {
    Start (ftp_cmd=USER);
    Stop (ftp_cmd=QUIT); // The response to the QUIT command will be assigned to the same Gop
    Extra (pasv_prt, pasv_addr);
};

Gop dns_req On dns_pdu Match (addr, addr, dns_id) {
    Start (dns_resp=0);
    Stop (dns_resp=1);
};

Gop isup_leg On isup_pdu Match (m3pc, m3pc, cic) {
    Start (isup_msg=1); // IAM
    Stop (isup_msg=16); // RLC
    Extra (calling, called);
};

If no Stop criterium is stated for a given Gop, the Gop will be stopped as soon as it is created. However, as with any other Gop, Pdus matching the Gop’s key will still be assigned to the Gop unless they match a Start condition, in which case a new Gop using the same key will be created.

...
mate dns_pdu:6->dns_req:1
    dns_pdu: 6
        dns_pdu time: 2.103063
        dns_pdu time since beginning of Gop: 2.103063
        dns_req: 1
            dns_req Attributes
                dns_id: 36012
                addr: 10.194.4.11
                addr: 10.194.24.35
            dns_req Times
                dns_req start time: 0.000000
                dns_req hold time: 2.103063
                dns_req duration: 2.103063
            dns_req number of PDUs: 2
                Start PDU: in frame 1
                Stop PDU: in frame 6 (2.103063 : 2.103063)
        dns_pdu Attributes
            dns_resp: 1
            dns_id: 36012
            addr: 10.194.4.11
            addr: 10.194.24.35

Note that there are two "timers" for a Gop:

So:

The first thing we have to do configuring a Gog is to tell MATE that it exists.

Gog web_use {
   ...
};

Then we have to tell MATE what to look for a match in the candidate Gops.

Gog web_use {
    Member http_ses (host);
    Member dns_req (host);
};

Most often, also other attributes than those used for matching would be interesting. In order to copy from Gop to Gog other interesting attributes, we might use Extra like we do for Gops.

Gog web_use {
    ...
    Extra (cookie);
};

mate http_pdu:4->http_req:2->http_use:1
    http_pdu: 4
        http_pdu time: 1.309847
        http_pdu time since beginning of Gop: 0.218930
        http_req: 2
            ... (the gop's tree for http_req: 2) ..
        http_use: 1
            http_use Attributes
                host: www.example.com
            http_use Times
                http_use start time: 0.000000
                http_use duration: 1.309847
            number of GOPs: 3
                dns_req: 1
                    ... (the gop's tree for dns_req: 1) ..
                http_req: 1
                    ... (the gop's tree for http_req: 1) ..
                http_req of current frame: 2

We can filter on:

AVPL Transformations are declared in the following way:

 Transform name {
   Match [Strict|Every|Loose] match_avpl [Insert|Replace] modify_avpl ;
   ...
 };

The name is the handle to the AVPL transformation. It is used to refer to the transform when invoking it later.

The Match declarations instruct MATE what and how to match against the data AVPL and how to modify the data AVPL if the match succeeds. They will be executed in the order they appear in the config file whenever they are invoked.

The optional match mode qualifier (Strict, Every, or Loose) is used to choose the match mode as explained above; Strict is a default value which may be omitted.

The optional modification mode qualifier instructs MATE how the modify AVPL should be used:

The modify_avpl may be an empty one; this comes useful in some cases for both Insert and Replace modification modes.

Examples:

 Transform insert_name_and {
   Match Strict (host=10.10.10.10, port=2345) Insert (name=JohnDoe);
};

adds name=JohnDoe to the data AVPL if it contains host=10.10.10.10 and port=2345

Transform insert_name_or {
   Match Loose (host=10.10.10.10, port=2345) Insert (name=JohnDoe);
};

adds name=JohnDoe to the data AVPL if it contains host=10.10.10.10 or port=2345

Transform replace_ip_address {
   Match (host=10.10.10.10) Replace (host=192.168.10.10);
};

replaces the original host=10.10.10.10 by host=192.168.10.10

Transform add_ip_address {
   Match (host=10.10.10.10) (host=192.168.10.10);
};

adds (inserts) host=192.168.10.10 to the AVPL, keeping the original host=10.10.10.10 in it too

 Transform replace_may_be_surprising {
   Match Loose (a=aaaa, b=bbbb) Replace (c=cccc, d=dddd);
 };

gives the following results:

Once declared, Transforms can be added to the declarations of PDUs, Gops or Gogs. This is done by adding the Transform name_list statement to the declaration:

Pdu my_proto_pdu Proto my_proto Transport ip {
    Extract addr From ip.addr;
    ...
    Transform my_pdu_transform[, other_pdu_transform[, yet_another_pdu_transform]];
};

Using Transforms we can add more than one start or stop condition to a Gop.

Transform start_cond {
  Match (attr1=aaa,attr2=bbb) (msg_type=start);
  Match (attr3=www,attr2=bbb) (msg_type=start);
  Match (attr5^a) (msg_type=stop);
  Match (attr6$z) (msg_type=stop);
};

Pdu pdu ... {
  ...
  Transform start_cond;
}

Gop gop ... {
  Start (msg_type=start);
  Stop (msg_type=stop);
  ...
}

Transform marks {
  Match (addr=10.10.10.10, user=john) (john_at_host);
  Match (addr=10.10.10.10, user=tom) (tom_at_host);
}

...

Gop my_gop ... {
  ...
  Transform marks;
}

After that we can use a display filter mate.gop.john_at_host or mate.gop.tom_at_host

Transform direction_as_text {
  Match (src=192.168.0.2, dst=192.168.0.3) Replace (direction=from_2_to_3);
  Match (src=192.168.0.3, dst=192.168.0.2) Replace (direction=from_3_to_2);
};

Pdu my_pdu Proto my_proto Transport tcp/ip {
  Extract src From ip.src;
  Extract dst From ip.dst;
  Extract addr From ip.addr;
  Extract port From tcp.port;
  Extract start From tcp.flags.syn;
  Extract stop From tcp.flags.fin;
  Extract stop From tcp.flags.rst;
  Transform direction_as_text;
}

Gop my_gop On my_pdu Match (addr,addr,port,port) {
  ...
  Extra (direction);
}

NAT can create problems when tracing, but we can easily worked around it by Transforming the NATed IP address and the Ethernet address of the router into the non-NAT address:

Transform denat {
  Match (addr=192.168.0.5, ether=01:02:03:04:05:06) Replace (addr=123.45.67.89);
  Match (addr=192.168.0.6, ether=01:02:03:04:05:06) Replace (addr=123.45.67.90);
  Match (addr=192.168.0.7, ether=01:02:03:04:05:06) Replace (addr=123.45.67.91);
}

Pdu my_pdu Proto my_proto transport tcp/ip/eth {
  Extract ether From eth.addr;
  Extract addr From ip.addr;
  Extract port From tcp.port;
  Transform denat;
}