Tunnel Switching Actions for L2TP AVPs at the Switching Boundary
When L2TP tunnel switching redirects packets to a different LNS, it performs one of the following default actions at the switching boundary for each AVP carried in the L2TP messages:
- regenerate—L2TP regenerates the AVP based on the local policy at the LTS and sent in the switched packet. The local policy may or may not use the value for the AVP received during negotiation for the first session.
- relay—L2TP transparently forwards the AVP in the switched packet with no alteration.
Table 1 lists the default action for each AVP. Mandatory AVPs are always included in the L2TP messages from the LAC; optional AVPs might be included in the messages.
You can optionally override the default action taken at the switching boundary for the Bearer Type AVP (18), Calling Number AVP (22), or Cisco NAS Port Info AVP (100). You can configure any of these three AVPs to be dropped from the switched packets or regenerated, or you can restore the default relay action.
 | Note: L2TP AVPs that have their attribute values hidden are always regenerated at the switching boundary. The value is decoded and sent in clear text when the packet is forwarded to the remote LNS. |
Table 1: Default Action for Handling L2TP AVPs at the Switching Boundary
AVP Name | AVP Type | L2TP Message Type | Default Action |
|---|---|---|---|
Assigned Session Id | Mandatory | ICRQ, CDN | Regenerate |
Assigned Tunnel Id | Mandatory | SCCRQ, CDN | Regenerate |
Bearer Capabilities | Optional | SCCRQ | Regenerate |
Bearer Type | Optional | ICRQ | Relay |
Call Serial Number | Mandatory | ICRQ | Relay |
Called Number | Optional | ICRQ | Relay |
Calling Number | Optional | ICRQ | Relay |
Challenge | Optional | SCCRQ | Regenerate |
Challenge Response | Optional | SCCCN | Regenerate |
Cisco NAS Port | Optional | ICRQ | Relay |
Failover Capability | Optional | SCCRQ | Regenerate |
Firmware Revision | Optional | SCCRQ | Regenerate |
Framing Capabilities | Mandatory | SCCRQ | Regenerate |
Framing Type | Mandatory | ICCN | Relay |
Host Name | Mandatory | SCCRQ | Regenerate |
Message Type | Mandatory | All | Regenerate |
Physical Channel Id | Optional | ICRQ | Regenerate |
Private Group Id | Optional | ICCN | Relay |
Protocol Version | Mandatory | SCCRQ | Regenerate |
Proxy Authentication | Optional | ICCN | Relay if acceptable; otherwise regenerate |
Proxy LCP | Optional | ICCN | Relay if acceptable; otherwise regenerate |
Receive Window Size | Optional | SCCRQ | Regenerate |
Rx Connect Speed | Optional | ICCN | Relay |
Sequencing Required | Optional | ICCN | Regenerate |
Sub-Address | Optional | ICRQ | Relay |
Tie Breaker | Optional | SCCRQ | Regenerate |
Tunnel Recovery | Optional | SCCRQ | Regenerate |
Tx Connect Speed | Mandatory | ICCN | Relay |
Vendor Name | Optional | SCCRQ | Regenerate |
