Brocade BigIron RX Series Configuration Guide - Manual (Page 245)

BigIron RX Series Configuration Guide 167
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Configuring IP parameters
7
Configuring the default gateway
To manage a device using Telnet or Secure Shell (SSH) CLI connections or the Web management
interface, you must configure an IP address for the device.
To configure a default gateway, first define an IP address by entering the command such as the
following.
BigIron RX(config-if-e1000-1/1)# ip address 192.45.6.110 255.255.255.0
Syntax: ip address <ip-addr> <ip-mask>
or
Syntax: ip address <ip-addr>/<mask-bits>
GRE IP tunnel
The BigIron RX allows the tunneling of packets of the following protocols over an IP network using
the Generic Router Encapsulation (GRE) mechanism as described in RFC 2784:
• OSPF
• BGP
• IS-IS point-to-point
Using this feature, packets of these protocols can be encapsulated inside a transport protocol
packet at a tunnel source and delivered to a tunnel destination where it is unpacked and made
available for delivery.
Figure 6 describes the GRE header format.
FIGURE 6 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 zero in transmitted
packets. If bits 11:7 of the field are non-zero, then a receiver must discard the packet unless RFC
1701 is implemented. This field is assumed to be zero in this version.
Ver – This field must be set to zero. This field is assumed to be zero in this version.
GRE MTU configuration considerations
The default value of IP GRE tunnel MTU is 1476 bytes. The MTU of the GRE tunnel is compared with
the outgoing packet before the encapsulation is done. After the encapsulation, the packet size
increases by 24 bytes. If a user wants to change the GRE tunnel MTU, the MTU should be at least
24 bytes less than the IP MTU of the outgoing interface. Otherwise, the size of the encapsulated
packet will exceed the IP MTU of the outgoing interface. In that case, the packet is dropped if the
DF (Do-Not-Fragment) bit is set in the original IP packet, otherwise, the packet is sent to CPU for
fragmentation.
Checksum Reserved0 Ver Protocol Type Checksum
(optional)
Reserved
(optional)
1 bit 12 bits 3 bits 16 bits 16 bits 16 bits