Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 742)

712 Multi-Service IronWare Switching Configuration Guide
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GRE IP tunnel
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• Fragmentation of the Inner packet as described in Section 3.4 of RFC 4459
This enhancement also allows you to set a specific MTU value for packets entering a configured
GRE tunnel. Packets whose size is greater than the configured value are fragmented and
encapsulated with IP/GRE headers for transit through the tunnel. This feature supports Jumbo
packets although they may be fragmented based on the MTU value configured.
Configuring a GRE IP Tunnel
To configure a GRE IP Tunnel, configure the following parameters:
• “CAM restrictions”
• Maximum Number of Tunnels (optional)
• Tunnel Interface
• Source Address or Source Interface for the Tunnel
• Destination address for the Tunnel
• GRE Encapsulation
• IP address for the Tunnel
• Keep Alive Support (optional)
• TTL Value (optional)
• TOS Value (optional)
• MTU Value (optional)
Configuration considerations
1. To enable keepalive when a GRE source and destination are directly connected, you must
disable ICMP redirect on the tunnel source port on the GRE nodes. Otherwise, the keepalive
packets go to the CPU where they can degrade CPU performance.
2. Whenever multiple IP addresses are configured on a tunnel source, the primary address of the
tunnel is always used for forming the tunnel connections. Consequently, you must carefully
check the configurations when configuring the tunnel destination.
3. GRE tunneling is not supported for non-default VRFs.
4. When a GRE tunnel is configured, you cannot configure the same routing protocol on the
tunnel through which you learn the route to the tunnel destination. For example, if the Brocade
device learns the tunnel destination route through OSPF protocol, you cannot configure the
OSPF protocol on the same Tunnel and vice-versa. When a tunnel has OSPF configured, the
Brocade device cannot learn the tunnel destination route through OSPF. This could cause the
system to become unstable.
NOTE
With GRE Dynamic-cam mode, at the Egress node, when a GRE packet is received, the Brocade
device programs the CAM entries to forward the packets based on Inner DPA. These host CAM
entries will be aging even if the traffic is hitting that CAM entries. This will cause the CAM entries to
become aged out and recreated which could cause a small packet loss.