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This document includes the following sections:
When Layer 2 Tunneling Protocol (L2TP) data packets are created, they have a Type of Service (TOS) field of zero, which indicates normal service. This ignores the TOS field of the encapsulated IP packets that are being tunneled. The L2TP Tunnel Preservation of IP TOS feature preserves quality of service for tunneled packets by copying the IP packets' TOS field onto the L2TP data packets when they are created at the L2TP Network Server's (LNS) virtual-access interface.
For more information about Cisco VPDN, see the following documents:
For descriptions of supported MIBs and how to use MIBs, see the Cisco MIB web site on CCO at http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml.
L2TP RFC
None
See the following sections for configuration tasks for the L2TP Tunnel Preservation of IP TOS feature. Each task in the list indicates if the task is optional or required.
| Step | Command | Purpose | ||
|---|---|---|---|---|
| Router(config)#vpdn-group 1 | Creates VPDN group 1. | ||
| Router(config-vpdn)#accept dialin | Enables the LNS to accept dialin requests. | ||
| Router(config-acc-in)# | Specifies L2TP as the tunneling protocol. Note L2TP is the only protocol that supports dialout and IP TOS preservation. | ||
| Router(config-acc-in)# | Specifies the number of the virtual template that is used to clone virtual-access interfaces. | ||
| Router(config-acc-in)# | Accepts tunnels that have this hostname configured as the hostname or as a localname. | ||
| Router(config-acc-in)# | Preserves the TOS field of the encapsulated IP packets. |
| Step | Command | Purpose | ||
|---|---|---|---|---|
| Router(config)#vpdn-group 1 | Creates VPDN group 1. | ||
| Router(config-vpdn)#request dialout | Enables the LNS to send L2TP dialout requests. | ||
| Router(config-req-out)# | Specifies L2TP as the tunneling protocol. Note L2TP is the only protocol that supports dialout and IP TOS preservation. | ||
| dupree(config-vpdn-req-out)#pool-member pool-number or dupree(config-vpdn-req-out)#rotary-group group-number | Specifies the dialer profile pool that will be used to dial out. Specifies the dialer rotary group that will be used to dial out. You can only configure one dialer profile pool or dialer rotary group. Attempting to configure a second dialer resource will remove the first from the configuration. | ||
| dupree(config-vpdn-req-out)#exit dupree(config-vpdn)#initiate-to ip ip-address [limit limit-number] [priority priority-number] | Specifies the IP address that will be dialed out. Optionally, you can configure a maximum number of connections that this VPDN group will support and the priority of this VPDN group. | ||
| dupree(config-vpdn)#local name hostname | Specifies that the L2TP tunnel will identify itself with this hostname. | ||
| dupree(config-vpdn)#l2tp ip tos reflect | Preserves the TOS field of the encapsulated IP packets. |
This section provides the following configuration examples:
vpdn-group 1 accept-dialin protocol l2tp virtual-template 1 terminate-from hostname althea local name bertha l2tp ip tos reflect
vpdn-group 1 request-dialout protocol l2tp pool-member 1 initiate-to ip 172.29.49.94 l2tp ip tos reflect
This section documents new or modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.0 command reference publications.
To configure a VPDN group to preserve the TOS field of L2TP-tunneled IP packets, use the l2tp ip tos reflect VPDN group command. To specify a TOS field of zero for tunneled packets, use the no form of this command.
l2tp ip tos reflectThis command has no keywords nor arguments.
Disabled
VPDN group mode
| Release | Modification |
|---|---|
12.0(5)T | This command was introduced. |
The l2tp ip tos reflect command can only be configured on LNS VPDN groups (VPDN groups that are configured to accept dial-in and/or request dialout sessions).
The following example shows an LNS configured to preserve IP TOS for L2TP dial-in sessions:
vpdn-group 1 accept-dialin protocol l2tp virtual-template 1 terminate-from hostname althea local name bertha l2tp ip tos reflect
The following examples shows an LNS configured to preserve IP TOS for L2TP dialout sessions:
vpdn-group 1 request-dialout protocol l2tp pool-member 1 initiate-to ip 172.29.49.94 l2tp ip tos reflect
| Command | Description |
request dialin | Enables a LAC to request either L2F or L2TP tunnels for dial-in. |
request dialout | Enables an LNS to request L2TP tunnels for dialout calls. |
Posted: Mon Oct 4 11:08:36 PDT 1999
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