Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 741)

Multi-Service IronWare Switching Configuration Guide 711
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GRE IP tunnel
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GRE IP tunnel
Multi-Service IronWare software supports the tunneling of packets with the Generic Routing
Encapsulation (GRE) mechanism over an IP network, as described in RFC 2784. With GRE, packets
are encapsulated in a transport protocol packet at a tunnel source and delivered to a tunnel
destination, where they are unpacked and made available for delivery.
Considerations in implementing this feature
The considerations in implementing this feature are as follows:
• As a point-to-point tunnel configuration, GRE requires both ends of the tunnel to be configured.
• Only four-byte GRE headers are supported at the ingress (even though eight-byte headers can
be processed at a transit node or the egress point).
• A Brocade device does not support the key and sequence numbering option with GRE (per RFC
2890).
• The current maximum number of tunnels is 8192 (with default as 256 tunnels).
NOTE
Do not forward packets from one type of tunnel to another type of tunnel in XPP. Packets may not be
routed properly.
Figure 188 describes the GRE header format.
FIGURE 188 GRE header format
Checksum – This field is assumed to be zero in this version. If set to 1 means that the Checksum
(optional) and Reserved (optional) fields are present and the Checksum (optional) field contains
valid information.
Reserved0 – Bits 6:0 of the field are reserved for future use and must be set to 0 in transmitted
packets. If bits 11:7 of the field are non-0, then a receiver must discard the packet. This field is
assumed to be 0 in this version.
Ver – This field must be set to 0. This field is assumed to be 0 in this version.
Protocol Type – This field contains the EtherType of the payload protocol.
For details on configuring a GRE IP tunnel, refer “To display the currently configured Martian
addresses refer to “Displaying martian addressing information”.” .
GRE MTU enhancements
Enhancements have been introduced to support GRE MTU in support of RFC 4459. This includes
support for the following:
• Signaling the Lower MTU to the Sources as described in Section 3.2 of RFC 4459