IP-in-IP decapsulation

IP-in-IP encapsulation involves the insertion of an outer IP header over the existing IP header. The source and destination addresses in the outer IP header point to the endpoints of the IP-in-IP tunnel. The stack of IP headers is used to direct the packet over a predetermined path to the destination, provided that the network administrator knows the loopback addresses of the routers transporting the packet. This tunneling mechanism can be used for determining availability and latency for most network architectures. The entire path from source to destination does not have to be included in the headers; a segment of the network can be chosen for directing the packets.

In IP-in-IP encapsulation and decapsulation, there are two types of packets. The original IP packets that are encapsulated are called inner packets, and the IP header stack added during encapsulation is called the outer packet.

Starting with Cisco IOS XR Release 7.3.5, the routers can handle multistack for-us packets within IP-in-IP tunnels efficiently. The for-us packets refer to IP packets with the source and destination terminating on the same router. Such packets are multistack when they undergo multiple layers of IP header encapsulation at ingress, loopback, and egress interfaces. With this improvement, your routers can identify IP packets with multistack tunneling IP header encapsulations and perform multiple IP header terminations on these packets. This capability enables you to configure IP packets to travel from the source endpoint to the destination endpoint and then back to the source, facilitating streamlined fault identification and isolation processes.

To debug faults in various large networks, you might have to capture and analyze the network traffic at a packet level. In data center networks, administrators face problems with the volume of traffic and the diversity of faults. To troubleshoot faults in a timely manner, data center network administrators must identify affected packets inside large volumes of traffic. They must track them across multiple network components, analyze traffic traces for fault patterns, and test or confirm potential causes.

In some networks, IP-in-IP decapsulation is used in network management to verify ECMP availability and to measure the latency of each path within a data center.

You can perform these actions to manage network traffic using IP-in-IP decapsulation:

• The Network Management System (NMS) sends IP-in-IP (IPv4 or IPv6) packets with a stack of predefined IPv4 or IPv6 headers (device IP addresses).

• The destination device removes the outer header at each hop.

• The device performs a lookup on the next header in the stack.

• The device forwards the packet if a valid route exists.

• Select specific ECMP links for troubleshooting by using the tunnel source direct command.

• Using the tunnel source direct command, you can choose specific IP Equal-Cost Multipath (ECMP) links for troubleshooting when there are multiple IP links between two devices.

• You can programmatically configure and manage the Ethernet interfaces using the openconfig-ethernet-if.yang and openconfig-interfaces.yang OpenConfig data models.

In IP-in-IP decapsulation, the router accepts a packet on a tunneled interface only when the tunnel IP address matches the source IP address of the incoming packets. With this implementation, you need to configure separate interface tunnels for each IP address for which the router receives traffic packets. This limitation often leads to configuration overload on the router.

You can eliminate the configuration overload on the router by assigning an object group as the tunnel destination for IPv4 and IPv6 traffic types. The router matches the source IP address of the incoming packet against the object group available as the tunnel destination. The decapsulation tunnel accepts the incoming traffic packets when there is a match between the packet source and the object group. Otherwise, the router drops the packets.