Configuring the Receive Window Size

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Configuring L2TP > Configuring the Receive Window Size
Configuring the Receive Window Size
You can configure the L2TP receive window size (RWS) for an L2TP tunnel. L2TP uses the RWS to implement a sliding window mechanism for the transmission of control messages.

When you configure the RWS, you specify the number of packets that the L2TP peer can transmit without receiving an acknowledgment from the router. If the RWS is not configured, the router determines the RWS and uses this value for all new tunnels on both the LAC and the LNS.

You can configure the L2TP RWS in the following ways:

Configure the systemwide default RWS setting for a tunnel on both the LAC and the LNS by using the l2tp tunnel default-receive-window command (in Global Configuration mode).

Configure the RWS for a tunnel on the LAC by using either the receive-window command (in Domain Map Tunnel Configuration mode) or by including the Tunnel-Receive-Window-Size RADIUS attribute (VSA 26-54) in RADIUS Access-Accept messages.

Configure the RWS for all tunnels that use a particular host profile on the LNS by using the receive-window command (in L2TP Destination Profile Host Configuration mode).

The following sections describe each of these methods for configuring the RWS.

Configuring the Default RWS

To configure the default RWS setting:
From Global Configuration mode, set the L2TP default RWS. The only value supported for the default RWS is 4.
host1(config)#l2tp tunnel default-receive-window 4
The router uses this RWS value for all new tunnels on both the LAC and the LNS.
(Optional) Use the show l2tp command to verify the default RWS configuration.
host1#show l2tp
Configuration
  L2TP administrative state is enabled
  Dynamic interface destruct timeout is 600 seconds
  Data packet checksums are disabled
  Receive data sequencing is not ignored
  Tunnel switching is disabled
  Retransmission retries for established tunnels is 5
  Retransmission retries for not-established tunnels is 5
  Tunnel idle timeout is 60 seconds
  Failover within a preference level is disabled
  Weighted load balancing is disabled
  Tunnel authentication challenge is enabled
  Calling number avp is enabled
  Ignore remote transmit address change is disabled
  Disconnect cause avp is disabled
  Default receive window size is 4
Sub-interfaces      total      active     failed     auth-errors
  Destinations      0          0          0          n/a
  Tunnels           0          0          0          0
  Sessions          0          0          0          n/a
  Switched-sessions 0          0          0          n/a
l2tp tunnel default-receive-window
Use to configure the default L2TP RWS for a tunnel on both the LAC and the LNS.

The default L2TP RWS is the number of packets that the L2TP peer can transmit without receiving an acknowledgment from the router. The only supported value is 4.

This command affects only those tunnels configured on the router after the command is issued; it has no effect on previously configured tunnels.

Example
host1(config)#l2tp tunnel default-receive-window 4
Use the no version to restore the default behavior, in which the router chooses the default L2TP RWS.
Configuring the RWS on the LAC

To configure the RWS for a tunnel on the LAC:
Access Domain Map Tunnel Configuration mode as described in Mapping a User Domain Name to an L2TP Tunnel. For example:
host1(config)#aaa domain-map fms.com
host1(config-domain-map)#router-name westford
host1(config-domain-map)#tunnel 3
host1(config-domain-map-tunnel)#
From Domain Map Tunnel Configuration mode, set the tunnel RWS. The only value supported for the tunnel RWS is 4, and it must be the same for all users of the same tunnel.
host1(config-domain-map-tunnel)#receive-window 4
(Optional) Use the show aaa domain-map command to verify the RWS configuration.
host1#show aaa domain-map
 
Domain: fms.com; router-name: westford; ipv6-router-name: default
                                                                 Tunnel
Tunnel   Tunnel   Tunnel   Tunnel   Tunnel    Tunnel    Tunnel   Client
 Tag      Peer    Source    Type    Medium   Password     Id      Name
------   ------   ------   ------   ------   --------   ------   ------
3        <null>   <null>   l2tp     ipv4     <null>     <null>   <null>
         Tunnel                 Tunnel
Tunnel   Server     Tunnel       Max      Tunnel
 Tag      Name    Preference   Sessions    RWS
------   ------   ----------   --------   ------
3        <null>   2000         0          4
You can also configure the RWS for a tunnel on the LAC by including the Tunnel-Receive-Window-Size RADIUS attribute (VSA 26-54) in RADIUS Access-Accept messages. For more information about RADIUS Access-Accept messages, see Chapter 2, Configuring RADIUS Attributes. For more information about the Tunnel-Receive-Window-Size attribute, see Appendix A, RADIUS Attribute Descriptions.

receive-window
Use to configure the L2TP RWS for a tunnel on the LAC.

The tunnel RWS is the number of packets that the L2TP peer can transmit without receiving an acknowledgment from the router. The only supported value supported is 4.

The RWS setting must be the same for all users of the same tunnel.

If you modify the RWS setting for an existing tunnel, subsequent tunnel users might be not be able to log in if their RWS setting conflicts with the new RWS setting for the tunnel.

Example
host1(config-domain-map-tunnel)#receive-window 4
Use the no version to revert to the systemwide RWS setting configured with the l2tp tunnel default-receive-window command.
Configuring the RWS on the LNS

To configure the RWS for a tunnel on the LNS:
Access L2TP Destination Profile Host Configuration mode as described in Configuring the LNS. For example:
host1(config)#virtual-router fms02
host1:fms02(config)#l2tp destination profile fms02 ip address 192.168.5.61
host1:fms02(config-l2tp-dest-profile)#remote host fms03
host1:fms02(config-l2tp-dest-profile-host)#
From Destination Profile Host Configuration mode, set the tunnel RWS. The only value supported for the tunnel RWS is 4.
host1:fms02(config-l2tp-dest-profile-host)#receive-window 4
(Optional) Use the show l2tp destination profile command to verify the RWS configuration.
host1:fms02#show l2tp destination profile fms02
L2TP destination profile fms02
Destination address
  Transport ipUdp
  Virtual router fms02
  Peer address 192.168.5.61
Host profile attributes
  Remote host is fms03
    Receive window size is 4
1 L2TP host profile found
receive-window
Use to configure the L2TP RWS for a tunnel on the LNS.

The RWS is the number of packets that the L2TP peer can transmit without receiving an acknowledgment from the router. The only value supported for the RWS is 4.

If you modify the RWS setting of a host profile for an existing tunnel, the router drops the tunnel. This action is consistent with router behavior when you modify an L2TP host profile.

Example
host1:boston(config-l2tp-dest-profile-host)#receive-window 4
Use the no version to revert to the systemwide RWS setting configured with the l2tp tunnel default-receive-window command.

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