ExtremeXOS 15.4 and above supports creating a GRE-based IPv4 tunnel, and routing IPv4 traffic over it. This feature is supported on all platforms that have GRE tunneling support (see ExtremeXOS 22.7 Feature License Requirements).
The switch administrator can configure a GRE tunnel by supplying the local source IPv4 address and the destination IPv4 address. Once configured, traffic can be redirected through the GRE tunnel. The TTL value of the outer IPv4 header will be set to 255 and the DSCP value is copied from the inner IPv4 header, the same as for the IPv6 tunnels. The encapsulated packets do not include the GRE checksum option, however if received with a checksum they are verified by the software, and then dropped if incorrect. The GRE module is capable of dealing with RFC 1701 neighbor options, with exception of the router option. Packets with this option set are dropped. However hardware does not support any options in the GRE header. If any of these options are set, the packet is either dropped, or sent to the CPU for processing. Since the key option of GRE tunnel is not configured, the GRE module only accepts GRE packets with a key value of 0, if present, and drops packets with other key values.
Note
GRE tunnels are IP tunnels which require L3 Function. L3 features are supported with EDGE license and above. All of the supported platforms' default license is EDGE or above, which include L3 features. In a stack all of the nodes must be GRE capable. For GRE in a stack, all stack nodes must be GRE hardware capable.All nodes in a stack need to support GRE tunnels, or else the feature cannot be configured/enabled. When all nodes in the system are capable of running GRE, new GRE tunnels can be created. If a new node is added to a stack, it will be powered on, and a log message is logged that the node is not compatible with GRE, and should be removed. This is done to prevent the node from continuously rebooting. If a system boots up with both a GRE configuration, and an incapable blade/node in the system, all GRE tunnels we be put in system disabled state. The “show tunnels” command displays this.
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