+ <dd>Optional. Compute GRE checksums on outgoing packets.
+ Checksums present on incoming packets will be validated
+ regardless of this setting. Note that GRE checksums
+ impose a significant performance penalty as they cover the
+ entire packet. As the contents of the packet is typically
+ covered by L3 and L4 checksums, this additional checksum only
+ adds value for the GRE and encapsulated Ethernet headers.
+ Default is disabled, set to <code>true</code> to enable.</dd>
+ </dl>
+ <dl>
+ <dt><code>pmtud</code></dt>
+ <dd>Optional. Enable tunnel path MTU discovery. If enabled
+ ``ICMP destination unreachable - fragmentation'' needed
+ messages will be generated for IPv4 packets with the DF bit set
+ and IPv6 packets above the minimum MTU if the packet size
+ exceeds the path MTU minus the size of the tunnel headers. It
+ also forces the encapsulating packet DF bit to be set (it is
+ always set if the inner packet implies path MTU discovery).
+ Note that this option causes behavior that is typically
+ reserved for routers and therefore is not entirely in
+ compliance with the IEEE 802.1D specification for bridges.
+ Default is enabled, set to <code>false</code> to disable.</dd>
+ </dl>
+ <dl>
+ <dt><code>header_cache</code></dt>
+ <dd>Optional. Enable caching of tunnel headers and the output
+ path. This can lead to a significant performance increase
+ without changing behavior. In general it should not be
+ necessary to adjust this setting. However, the caching can
+ bypass certain components of the IP stack (such as IP tables)
+ and it may be useful to disable it if these features are
+ required or as a debugging measure. Default is enabled, set to
+ <code>false</code> to disable.</dd>
+ </dl>
+ </dd>
+ <dt><code>capwap</code></dt>
+ <dd>Ethernet tunneling over the UDP transport portion of CAPWAP
+ (RFC 5415). This allows interoperability with certain switches
+ where GRE is not available. Note that only the tunneling component
+ of the protocol is implemented. Due to the non-standard use of
+ CAPWAP, UDP ports 58881 and 58882 are used as the source and
+ destinations ports respectivedly. Each tunnel must be uniquely
+ identified by the combination of <code>remote_ip</code> and
+ <code>local_ip</code>. If two ports are defined that are the same
+ except one includes <code>local_ip</code> and the other does not,
+ the more specific one is matched first. CAPWAP support is not
+ available on all platforms. Currently it is only supported in the
+ Linux kernel module with kernel versions >= 2.6.25. The following
+ options may be specified in the <ref column="options"/> column:
+ <dl>
+ <dt><code>remote_ip</code></dt>
+ <dd>Required. The tunnel endpoint.</dd>
+ </dl>
+ <dl>
+ <dt><code>local_ip</code></dt>
+ <dd>Optional. The destination IP that received packets must
+ match. Default is to match all addresses.</dd>
+ </dl>
+ <dl>
+ <dt><code>tos</code></dt>
+ <dd>Optional. The value of the ToS bits to be set on the
+ encapsulating packet. It may also be the word
+ <code>inherit</code>, in which case the ToS will be copied from
+ the inner packet if it is IPv4 or IPv6 (otherwise it will be
+ 0). Note that the ECN fields are always inherited. Default is
+ 0.</dd>
+ </dl>
+ <dl>
+ <dt><code>ttl</code></dt>
+ <dd>Optional. The TTL to be set on the encapsulating packet.
+ It may also be the word <code>inherit</code>, in which case the
+ TTL will be copied from the inner packet if it is IPv4 or IPv6
+ (otherwise it will be the system default, typically 64).
+ Default is the system default TTL.</dd>