Cisco Cisco IOS Software Release 12.0(21)S

GRE tunneling on an E2 POS tunnel server card provides an aggregate throughput of approximately 2.7 Mpps 
of tunnel traffic. Also, ingress and egress line cards can run any feature loads that a customer requires.

GRE tunneling does not impact the performance of the normal IP forwarding path on the Cisco 12000 
series Internet router. The performance of other IP tunnel protocols (UTI raw, FR UTI, and so on) is, 
however, affected if they run at the same time because they share the bandwidth that is available on the 
tunnel server card. A maximum of 2.7 Mpps of traffic is supported on the tunnel server card.

You can specify a maximum of 128 unique IP interfaces as GRE tunnel sources on a Cisco 12000 
series Internet router.

Each unique GRE bound IP interface can have a maximum of 500 tunnels destined to it.

The Cisco 12000 series Internet router supports up to a maximum of 500 GRE tunnels.

Cisco Express Forwarding (CEF)

On a Cisco 12000 series Internet router, the following line cards support GRE tunneling on 
customer-facing interfaces:

Engine 0

1-Port OC-12 POS

2-Port Channelized OC-3/STM-1 (DS1/E1)

6-Port Channelized T3 (T1)