Cisco N7K-C7010 Configuration Guide - Page 267
Path MTU Discovery, Virtualization Support, High Availability, Licensing Requirements for IP Tunnels
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Chapter 8 Configuring IP Tunnels Licensing Requirements for IP Tunnels Send document comments to [email protected] Path MTU Discovery Path maximum transmission unit (MTU) discovery (PMTUD) prevents fragmentation in the path between two endpoints by dynamically determining the lowest MTU along the path from the packet's source to its destination. PMTUD reduces the send MTU value for the connection if the interface receives information that the packet would require fragmentation. When you enable PMTUD, the interface sets the Don't Fragment (DF) bit on all packets that traverse the tunnel. If a packet that enters the tunnel encounters a link with a smaller MTU than the MTU value for the packet, the remote link drops the packet and sends an ICMP message back to the sender of the packet. This message indicates that fragmentation was required (but not permitted) and provides the MTU of the link that dropped the packet. Note PMTUD on a tunnel interface requires that the tunnel endpoint can receive ICMP messages generated by devices in the path of the tunnel. Check that ICMP messages can be received before using PMTUD over firewall connections. Virtualization Support You can configure IP tunnels only in the default virtual device context (VDC) and the default Virtual Routing and Forwarding (VRF) instance. Beginning with Cisco NX-OS Release 4.2, you can configure a tunnel interface as a member of a Virtual Routing and Forwarding (VRF) instance and as a member of any VDC. By default, Cisco NX-OS places you in the default VDC and default VRF unless you specifically configure another VDC and VRF. A tunnel configured in one VDC is isolated from a tunnel with the same number configured in another VDC. For example, Tunnel 0 in VDC 1 is independent of tunnel 0 in VDC 2. Your tunnel source IP address and destination IP address should be in the same VRF. You can also configure what VRF to use to look up the tunnel destination. This VRF should match the VRF of the tunnel source IP address. See the Cisco Nexus 7000 Series NX-OS Virtual Device Context Configuration Guide, Release 5.x, for information about VDCs and see the Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 5.x, for information about VRFs. High Availability IP tunnels support stateful restarts. A stateful restart occurs on a supervisor switchover. After the switchover, Cisco NX-OS applies the runtime configuration after the switchover. Licensing Requirements for IP Tunnels The following table shows the licensing requirements for this feature: Product Cisco NX-OS License Requirement IP tunnels require an Enterprise Services license. For a complete explanation of the Cisco NX-OS licensing scheme and how to obtain and apply licenses, see the Cisco NX-OS Licensing Guide. OL-23435-03 Cisco Nexus 7000 Series NX-OS Interfaces Configuration Guide, Release 5.x 8-3