5-4 Serial Tunnel (STUN) | Cisco Field Manual[c] Router Configuration

STUN provides tunneling of the Synchronous Data Link Control (SDLC) protocol across a multiprotocol network.
An SDLC device can connect to one router's serial port and communicate transparently with another SDLC device on a distant router's serial port.
STUN can transport SDLC over TCP/IP and HDLC protocols.
STUN can provide local acknowledgment to attached SDLC devices, preventing session timeouts and losses due to high latency or low speeds of WAN networks.
SDLC encapsulated within TCP can also benefit from priority queuing.

NOTE

STUN uses the following TCP port numbers : 1994 (high priority), 1990 (medium priority), 1991 (normal priority, the default), and 1992 (low priority).

Configuration

Define a remote STUN peer:

 (global)  stun peer-name   ip-address

(Optional) Set up the SDLC FF broadcast address.

If the router is acting in a secondary SDLC role and is emulating a multidrop connection to several remote STUN peers, the multidrop must also emulate broadcast transmission.
1. Enable broadcast replication:
```
 (interface)  sdlc virtual-multidrop  
```
  By definition, the SDLC address FF is always used as a broadcast address for all devices on an SDLC connection. The virtual multidrop causes the router to replicate any SDLC FF broadcast frames to all STUN peers that have an FF address.
2. Define a static mapping for SDLC FF to each STUN peer:
```
 (interface)  stun route address ff tcp   ip-address  
```
  -OR-
```
 (interface)  stun route address ff interface serial   number  
```
  -OR-
```
 (interface)  stun route address ff   interface   frame-relay-int   dlci   dlci   localsap  
```
  The broadcast address FF is mapped to a remote peer, according to the STUN transport type being used: tcp (TCP/IP, the peer's IP address), interface serial (HDLC, the serial interface number), or interface frame-relay-int (Frame Relay, the interface with DLCI and the local connecting SAP number).
Define the type of traffic to transport.
1. (Custom non-SDLC protocol transport only) Create a custom protocol schema for STUN:
```
 (global)  stun schema   name   offset   offset   length   address-length   format   format  
```
  name is the custom protocol (1 to 20 characters ). The address field is always found at offset bytes within the frame and is address-length bytes long. Addresses for this protocol are presented in the format decimal, hexadecimal, or octal.
2. Assign the interface to a protocol group :
```
 (global)  stun protocol-group   group-number  {  basic   sdlc  [  sdlc-tg  ]  schema  } 
```
  STUN can carry several types of protocols. Each STUN interface must be assigned to a protocol group, according to the type of protocols being transported: sdlc (SDLC protocols; use sdlc-tg to identify with an SNA transmission group), basic (any non-SDLC protocols), or schema (a custom protocol defined with stun schema ).
Use STUN keepalives .
1. Set the number of keepalive attempts:
```
 (global)  stun keepalive-count   count  
```
  The router attempts to send an unresponsive peer count (2 to 10) of keepalives before declaring the peer connection to be down.
2. (Optional) Set the keepalive interval:
```
 (global)  stun remote-peer-keepalive   seconds  
```
  Keepalive messages are sent to and expected from remote peers at intervals of seconds (1 to 300; the default is 30 seconds).
Enable STUN on a serial interface.
1. Use STUN encapsulation:
```
 (interface)  encapsulation stun  
```
2. Assign the interface to a STUN protocol group:
```
 (interface)  stun group   group-number  
```
  The interface tunnels the protocols defined in the STUN group (1 to 255). The interfaces on remote peers must be defined to the same protocol group before traffic is tunneled.
Define tunneled SDLC addresses and the STUN encapsulation type.
1. (Optional) Tunnel traffic from all SDLC addresses:
```
 (interface)  stun route all tcp   ip-address  
```
  -OR-
```
 (interface)  stun route all interface serial   number  [  direct  ] 
```
  STUN transports traffic from all SDLC addresses on the SDLC serial interface. The STUN encapsulation type to the remote peer can be set to tcp (TCP/IP, the peer's IP address) or interface serial (HDLC, the serial interface number ). The direct keyword can be used if serial encapsulation is used and it is a direct STUN link (not a serial connection to a router).
2. Tunnel traffic from specific SDLC addresses:
```
 (interface)  stun route address   sdlc-address   tcp   ip-address  [  local-ack  ]   [  priority  ] [  tcp-queue-max  ] 
```
  -OR-
```
 (interface)  stun route address   sdlc-address   interface serial   number  [  direct  ] 
```
  -OR-
```
 (interface)  stun route address   sdlc-address   interface   frame-relay-int   dlci   dlci localsap  [  local-ack  ] 
```
  SDLC traffic from sdlc-address (two hex digits, 01 to FE) is transported to the STUN peer given by tcp (TCP/IP, the peer's IP address), interface serial (HDLC, the serial interface number ), or interface frame-relay-int (Frame Relay, the interface, DLCI, and localsap [the local connecting SAP]).
  
  The local-ack keyword can be given to provide local acknowledgment to the SDLC device, rather than letting the device wait for an acknowledgment to return over the network. If the network has slow WAN links or high latency, local acknowledgment can help keep sessions from timing out or being lost.
  
  With TCP encapsulation, the priority keyword can be used to provide priority queuing of STUN traffic. The tcp-queue-max keyword can be used to set the maximum size of the outbound TCP queue (the default is 100 packets).
Use local acknowledgment:
```
 (interface)  stun sdlc-role  {  primary   secondary  } 
```
To provide local acknowledgment, the router must be set to operate in the SDLC role: primary ( polls secondary nodes) or secondary (sends data only when polled by the primary). In general, a front-end processor (FEP) is a primary node, and an establishment controller (EC) is a secondary node. The router must play the opposite role of the device it is connected to. For example, a router connected to a controller must act like the FEP (primary), whereas a router connected to a FEP must act like a controller (secondary).
Use priority queuing.
1. Priority traffic according to the serial address.
  - Define the priority queues and their TCP ports:
```
 (global)  priority-list   list-num   protocol ip high tcp 1994  (global)  priority-list   list-num   protocol ip medium tcp 1990  (global)  priority-list   list-num   protocol ip normal tcp 1991  (global)  priority-list   list-num   protocol ip low tcp 1992  
```
    A priority queuing list numbered list-num (1 to 10) is created, and a queue for each priority level is defined as a specific TCP port number. The numbers shown are the accepted standard, but you can change them by replacing them with other port numbers.
  - Assign a priority queue to a serial interface address:
```
 (global)  priority-list   list-num   stun   queue   address   group-number address  
```
    The serial device address (for example, a two-digit hexadecimal SDLC address) from STUN protocol group group-number (1 to 255) is assigned a priority queue ( high, normal, medium, or low ) from the priority-list list-num (1 to 10).
  - Apply a priority queue list to a STUN interface:
```
 (interface)  priority-group   list-num  
```
    The priority list list-num is used to classify inbound STUN traffic and place it in the appropriate priority queues. Traffic is then processed according to the TCP port that was assigned to the various queues.
2. Prioritize traffic according to the Logical Unit (LU) number.
  - Define the priority queues and their TCP ports:
```
 (global)  priority-list   list-num   protocol ip high tcp 1994  (global)  priority-list   list-num   protocol ip medium tcp 1990  (global)  priority-list   list-num   protocol ip normal tcp 1991  (global)  priority-list   list-num   protocol ip low tcp 1992  
```
    A priority queuing list numbered list-num (1 to 10) is created, and a queue for each priority level is defined as a specific TCP port number. The numbers shown are the accepted standard, but you can change them by replacing them with other port numbers.
  - Assign a priority queue to a specific LU address:
```
 (global)  locaddr-priority-list   lu-list lu-address queue  
```
    An LU priority list numbered lu-list (1 to 10) is created. It contains a set of LU-to-queue mappings. The LU address given by lu-address (a two-digit hex address) is assigned to the priority queue named queue ( high, normal, medium, or low ).
  - Apply the LU priority list to an inbound STUN interface:
```
 (interface)  locaddr priority   lu-list  
```
    The LU priority list numbered lu-list (1 to 10) is used to classify inbound serial traffic into the different priority queues.
  - Apply a priority queue list to an outbound interface:
```
 (interface)  priority-group   list-num  
```
    The priority list list-num is used to perform priority queuing according to the classification that was assigned by the LU priority list.

Example

A router connects to a serial SDLC line-sharing device over interface serial 1. STUN is configured to tunnel all SDLC devices to the remote peer router at 172.19.76.41. The STUN interface must become a primary role, polling the end SDLC devices. Because multiple devices exist on the SDLC interface, the virtual multidrop is used along with a static routing of SDLC address FF to the remote peer for broadcasts.

STUN prioritization is configured so that traffic from SDLC device B1 receives a high priority and device C1 receives normal priority. Figure 5-5 shows a network diagram.

Figure 5-5. Network Diagram for the Example

graphics/05fig05.gif

  stun peer-name 172.19.76.41   stun protocol-group 3 sdlc   interface serial 1   ip address 192.168.14.2 255.255.255.0   encapsulation stun   stun group 3   stun route all 172.19.76.41 local-ack priority   stun sdlc-role primary   sdlc virtual-multidrop   stun route address ff tcp 172.19.76.41   priority-group 1   priority-list 1 protocol ip high tcp 1994   priority-list 1 protocol ip medium tcp 1990   priority-list 1 protocol ip normal tcp 1991   priority-list 1 protocol ip low tcp 1992   priority-list 1 stun high address 3 B1   priority-list 1 stun normal address 3 C1