Manual

Layer 2 Tunnel Protocol Version 3
Restrictions for Layer 2 Tunnel Protocol Version 3
6
Cisco IOS Releases 12.0(29)S and 12.2(25)S
• On the Cisco 10720 Internet router, the uti translation command is not migrated for Xconnect
service and is not supported. Although the uti command is supported in L2TPv3 releases, the
translation option is lost in the migration.
• On the Cisco 10720 Internet Router, although it is not required, it is highly recommended that you
configure a loopback interface as the IP local interface.
You can also configure a LAN interface as the IP local interface so that the tunnel control session is
tied to an operational LAN (Gigabit Ethernet or Fast Ethernet) interface or subinterface. However,
in this case, the tunnel control plane is used only as long as the Gigabit Ethernet or Fast Ethernet
interface is operational.
Cisco 12000 Series-Specific Restrictions
• IS-IS protocol packet fragmentation is supported only for dynamic L2TPv3 sessions.
• The IP local interface must be a local loopback interface. Configuring any other interface as the IP
local interface will result in nonoperational sessions.
• The IP local interface must be dedicated for the use of L2TPv3 sessions. This interface must not be
shared by any other routing or tunneling protocols.
• Hairpinning is not supported for local-to-local switching. The start and end of an L2TPv3 session
must terminate on different routers linked via an IP or MPLS backbone.
• The aggregate performance is bound by the server card limit of 2.5 million packets per second (pps).
• The dedicated tunnel server card 1-port OC-48c/STM-16c POS/SDH is required for L2TPv3 to
function. The server card will not run any Engine 2 features.
• The ip unnumbered command and IP address should be configured under the PoS interface of the
server card prior to hardware-module configuration. This configuration makes the server card
IP-aware for backbones requiring an Address Resolution Protocol (ARP) to be generated by the line
card. The backbone types that require this configuration are Ethernet and spatial reuse protocol
(SRP). This configuration is also a requirement for session keepalives. The interface port of the
server card will automatically be set to loopback internal and no keepalives once the hw-module
slot slot-number mode server command is configured.
• Due to a framer problem, the server card interfaces accounting in (packets out) will not be accurate.
• Only features found in the Vanilla uCode bundle are supported on Engine 2 line cards that are
associated with an L2TPv3 session and on a different interface, DLCI, or VLAN of the same line
card.
• Configuring Engine 2 features not found in the Vanilla uCode bundle on any port of the Engine 2
line card that has a L2TPv3 session bound to one or more interfaces will cause the Vanilla uCode to
be swapped out. This configuration will cause all traffic through the L2TPv3 session to stop on that
Engine 2 line card. In this case, rebinding of the L2TPv3 session will be required when the Vanilla
uCode bundle is restored.
• Configuring output access control lists (ACLs) on any line card will swap out the running Engine 2
line card Vanilla uCode bundle in favor of the ACL uCode bundle. This configuration will cause all
traffic through the L2TPv3 session to stop on those Engine 2 line cards. If output ACLs are essential
on the router, it is advisable to originate all L2TPv3 sessions on Engine 0 line cards. Output ACLs
will not swap out the server card uCode bundle due to the higher priority.
• Engine 2 line cards do not support Frame Relay switching and Frame Relay L2TPv3 DLCI session
on the same line card.