Configuration Guide User guide

1044 FastIron Configuration Guide
53-1002494-02
IPv4 point-to-point GRE tunnels
IPv4 GRE tunnel overview
Generic Routing Encapsulation is described in RFC 2784. Generally, GRE provides a way to
encapsulate arbitrary packets (payload packet) inside of a transport protocol, and transmit them
from one tunnel endpoint to another. The payload is encapsulated in a GRE packet. The resulting
GRE packet is then encapsulated in a delivery protocol, then forwarded to the tunnel destination. At
the tunnel destination, the packet is decapsulated to reveal the payload. The payload is then
forwarded to its final destination.
Brocade IPv6-capable devices allow the tunneling of packets of the following protocols over an IPv4
network using GRE:
• OSPF V2
• BGP4
• RIP V1 and V2
NOTE
This is not supported on ICX 6450 devices.
GRE packet structure and header format
Figure 123 shows the structure of a GRE encapsulated packet.
FIGURE 123 GRE encapsulated packet structure
Figure 124 shows the GRE header format.
FIGURE 124 GRE header format
The GRE header has the following fields:
• Checksum – 1 bit. This field is assumed to be zero in this version. If set to 1, this means that
the Checksum (optional) and Reserved (optional) fields are present and the Checksum
(optional) field contains valid information.
• Reserved0 – 12 bits. If bits 1 - 5 are non-zero, then a receiver must discard the packet unless
RFC 1701 is implemented. Bits 6 - 12 are reserved for future use and must be set to zero in
transmitted packets. This field is assumed to be zero in this version.
Delivery Header
GRE Header
Payload Packet
Checksum Ver Protocol Type Reserved0 Checksum
(optional)
Reserved
(optional)