Manual

Layer 2 Tunnel Protocol Version 3
Restrictions for Layer 2 Tunnel Protocol Version 3
5
Cisco IOS Releases 12.0(29)S and 12.2(25)S
• The number of sessions on a PPP, high-level data link control (HDLC), Ethernet, or 802.1q VLAN
port is limited by the number of interface descriptor blocks (IDBs) that the router can support. For
PPP, HDLC, Ethernet, and 802.1q VLAN circuit types, an IDB is required for each circuit.
When L2TPv3 is used to tunnel Frame Relay D channel data-link connection identifiers (DLCIs),
an IDB is not required for each circuit. As a result, the memory requirements are much lower. The
scalability targets for the Engineering Field Test (EFT) program are 4000 L2TP session.
• Frame Relay support includes only 10-bit DLCI addressing. The L2TPv3 feature does not support
Frame Relay extended addressing.
• The interface keepalive feature is automatically disabled on the interface to which Xconnect is
applied, except for Frame Relay encapsulation, which is required for Local Management Interface
(LMI).
• Static L2TPv3 sessions do not support Frame Relay LMI interworking.
• Static L2TPv3 sessions do not interoperate with Universal Tunnel Interface (UTI) using keepalives.
• The ip pmtu command used to configure the pseudowire class (see the section “Configuring the
L2TPv3 Pseudowire”) is not supported for static L2TPv3 sessions. As a result, IP packet
fragmentation and Intermediate System-to-Intermediate System (IS-IS) fragmentation through a
static L2TPv3 session are not supported.
• IP packet fragmentation is not supported when the CE router is running special Layer 2 options such
as Layer 2 sequencing, compression, or encryption. Examples of these options are Frame Relay
compression and fragmentation or PPP compression. In these scenarios, the IP payload is not in a
format that is compatible with IP fragmentation.
Cisco 7200-Specific Restrictions
• ATM port mode cell relay is supported only on the PA-A3-T3, PA-A3-E3, and PA-A3-OC3 ATM
port adapters.
• VPI or VPI/VCI rewrite is not supported for any ATM transport mode. The peer routers must be
configured with matching VPI or VCI values.
Cisco 7500-Specific Restrictions
• Distributed sequencing is supported on Cisco 7500 series routers only. The ip cef distributed
command must be configured.
• ATM port mode cell relay is supported only on the PA-A3-T3, PA-A3-E3, and PA-A3-OC3 ATM
port adapters.
• VPI or VPI/VCI rewrite is not supported for any ATM transport mode. The peer routers must be
configured with matching VPI or VCI values.
Cisco 10720-Specific Restrictions
• Variable cookie size, IP packet fragmentation, and L2TPv3 sequencing are not supported.
• The reassembly of fragmented L2TPv3 packets is performed on the Cisco 10720 Internet Router by
the Route Processor (RP) at the process level, not in the Parallel eXpress Forwarding (PXF)
forwarding path.