Gre Tunneling; Encapsulation And De-Encapsulation On The Router; Number Of Source And Destination Tunnels Allowed On A Router - Juniper ACX1000 Configuration Manual

ACX Series Universal Access Router Configuration Guide

GRE Tunneling

582
NOTE: Service chaining for GRE, NAT, and IPSec services on ACX1100-AC
and ACX500 routers is not supported.
Data is routed by the system to the GRE endpoint over routes established in the route
table. (These routes can be statically configured or dynamically learned by routing
protocols such as RIP or OSPF.) When a data packet is received by the GRE endpoint, it
is de-encapsulated and routed again to its destination address.
GRE tunnels are stateless-–that is, the endpoint of the tunnel contains no information
about the state or availability of the remote tunnel endpoint. Therefore, the router
operating as a tunnel source router cannot change the state of the GRE tunnel interface
to down if the remote endpoint is unreachable.
For details about GRE tunneling, see:
Encapsulation and De-Encapsulation on the Router on page 582
Number of Source and Destination Tunnels Allowed on a Router on page 582

Encapsulation and De-Encapsulation on the Router

Encapsulation—A router operating as a tunnel source router encapsulates and forwards
GRE packets as follows:
When a router receives a data packet (payload) to be tunneled, it sends the packet
1.
to the tunnel interface.
The tunnel interface encapsulates the data in a GRE packet and adds an outer IP
2.
header.
The IP packet is forwarded on the basis of the destination address in the outer IP
3.
header.
De-encapsulation—A router operating as a tunnel remote router handles GRE packets
as follows:
When the destination router receives the IP packet from the tunnel interface, the outer
1.
IP header and GRE header are removed.
The packet is routed based on the inner IP header.
2.

Number of Source and Destination Tunnels Allowed on a Router

ACX routers support as many as 64 GRE tunnels between routers transmitting IPv4 or
IPv6 payload packets over GRE.
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