Brocade ICX 6650 Layer 3 Routing Configuration Guide 95
53-1002603-01
IPv4 point-to-point GRE tunnels
Example
To create the configuration indicated in Figure12 and Figure 13, enter commands such as the
following.
Brocade(config)# dhcp-gateway-list 1 192.168.5.1
Brocade(config)# dhcp-gateway-list 2 10.95.6.1
Brocade(config)# dhcp-gateway-list 3 10.95.1.1 10.95.5.1
Brocade(config)# interface ethernet 1/1/2
Brocade(config-if-e10000-1/1/2)# dhcp-gateway-list 1
Brocade(config-if-e10000-1/1/2)# interface ethernet 1/1/8
Brocade(config-if-e10000-1/1/8)# dhcp-gateway-list 3
Brocade(config-if-e10000-1/1/8)# interface ethernet 1/1/14
Brocade(config-if-e10000-1/1/14)# dhcp-gateway-list 2
Syntax: dhcp-gateway-list num ip-addr
IPv4 point-to-point GRE tunnels
This section describes support for point-to-point Generic Routing Encapsulation (GRE) tunnels and
how to configure them on a Brocade device.
GRE tunnels support includes, but is not limited to, the following:
IPv4 over GRE tunnels. IPv6 over GRE tunnels is not supported.
Static and dynamic unicast routing over GRE tunnels
Multicast routing over GRE tunnels
Hardware forwarding of IP data traffic across a GRE tunnel.
Path MTU Discovery (PMTUD)

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

GRE packet structure and header format

Figure 14 shows the structure of a GRE encapsulated packet.