Cisco 7600 Series Router Software Configuration Guide, Cisco IOS Release 15S

Restrictions for VRF aware IPv6 tunnels

Following restrictions apply to the VRF aware IPv6 tunnels feature:

• This feature supports the IPv6IP and 6to4 tunnels mode.
• Due to EARL limitation, the same source tunnels across VRFs are not supported.
• The tunnel source and the tunnel destination should be in the same VRF instance.
• The tunnel IPv4 transport addresses and the physical interface where the tunnel traffic exits, should be in the same VRF instance.
• The incoming IPv6 interface and the tunnel should be in the same VRF instance.
• This feature does not support IPv6IP auto-tunnels and ISATAP.

Tunnel SSO

An IP tunnel is an IP network communications channel between two networks. It is used to transport another network protocol by packet encapsulation.

The IP Tunnel-SSO feature provides the following benefits:

• Cisco Nonstop Forwarding (NSF) works with the Stateful Switchover (SSO): In a distributed system with an active RP and a standby RP, check the necessary state on the standby RP to see if the loss of the packets sent or received on a tunnel interface is eliminated during a switchover.

Note Hardware limitations may result in packet loss.

• In-Service Software Upgrade (ISSU): Allows the upgrade or downgrade from a version to another for IOS that supports tunnel HA with minimal packet loss.
• Uplink forwarding: Enables the ports on the standby RP of an HA system to switch traffic between tunnel endpoints.
• Solve the problems caused by the race conditions in distributed systems: In the current IP tunnel feature, many packets for tunnel forwarding are sent from the RP to line cards using the XDR DRAM. These packets should arrive on the line cards in a particular order, which is not guaranteed every time due to line card inconsistencies. The IP Tunnel-SSO feature helps prevent these race conditions.

Note To minimize packet loss during switchover, all the relative components in the network need to be HA capable.

Supported Tunnel Types

The followings are the tunnel types that support HA:

• IPv4 over GRE (tunnel mode GRE)
• IPv4 over IPv4 (tunnel mode IPv4IP)
• IPv6 over GRE (tunnel mode GRE)
• IPv6 over IPv4 (tunnel mode IPv6IP)
• 6to4 tunneling (tunnel mode IPv6IP 6 to 4)
• 6RD (tunnel mode IPv6IP 6RD)
• MPLSoGRE
• MPLSoGRE Same Source tunnels
• MPLSoMGRE

Restrictions

MDT and MPLS-TE tunnels do not support HA.

Restrictions for IPv6 over IPv4-GRE tunnel

Following restrictions apply to the IPv6 over IPv4-GRE tunnel:

• The IPv4 tunnel facing interface must be on the ES+ line card.
• The GRE tunnel key is not supported in the hardware.
• The IPv4 fragmentation after tunnel encapsulations is not supported in the hardware.
• The fragmented IPv4 packets for tunnel decapsulations is not supported in the hardware.
• The IPv4 GRE keepalives are supported, but the IPv6 GRE keepalives are not supported.
• The keepalives are not supported when the VRF instances configured using the vrf forwarding and tunnel vrf commands are different.
• Due to EARL limitation, same source tunnels across VRF’s are not supported.
• This feature is not SSO compliant.
• With scaled configurations, when changing the tunnel mode from IPv6 over GRE to IPv6IP and on enabling the mls mpls tunnel-recirc command, the system displays an error message with a trace back.