3Com Switch 8800 Advanced Software V5 Configuration Guide

410 CHAPTER 34: GRE CONFIGURATION
■ For a tunnel interface that is configured with any of the above features, all the
configuration disappears once that interface is deleted.
■ The source address and destination address of a tunnel uniquely identify a
path. They must be configured at both ends of the tunnel and are mutually the
source address and the destination address.
■ Two or more tunnel interfaces using the same encapsulation protocol must
have different source addresses and destination addresses.
■ If you configure a source interface for a tunnel interface, the source address of
the tunnel interface is the primary IP address of the source interface.
■ The source and destination addresses of a tunnel must be different from each
other. Moreover, for static routes configured on a tunnel interface, their
destination addresses cannot be in the same network segment as the address
of that tunnel interface.
■ When you configure a route through the tunnel, you can configure a static
route, whose destination address is the destination address of the packet not
encapsulated in GRE and next hop is the address of the tunnel interface at the
remote end. Or, you can enable the dynamic routing protocol on both the
tunnel interface and the router interface connecting the private network so
that the dynamic routing protocol can establish a routing entry that allows the
tunnel to forward packets through the tunnel.
■ IPv6 over IPv4 GRE tunnel interfaces support such dynamic routing protocols as
OSPFv3, RIPng and BGP4+.
■ To run dynamic routing protocols (apart from BGP4+) on a tunnel interface,
you need to enable the expediting function on the relevant tunnel first.
■ It is not allowed to set up on a tunnel interface static routes whose destination
addresses are in the network segment as that tunnel interface.
■ For GRE IPv6 over IPv4 packets, due to restrictions of match conditions for the
expediting function, only the physical ports with the link type as Access or
Hybrid can be bound to the VLAN interface that acts as the source interface of
a tunnel. Moreover, when the link type of a port is Hybrid, the untagged
attribute must be specified for the VLAN that sends GRE tunnel packets.
■ The 3C17526 and 3C17532 modules do not support the expediting function
on GRE IPv6 over IPv4 tunnels.
Displaying and
Maintaining GRE
To do... Use the command... Remarks
Display information about a
specified or all tunnel
interfaces
display interface tunnel [
number ]
Available in any view
Display IPv6 information
about a tunnel interface
display ipv6 interface
tunnel number
Available in any view