CPU-based packet generators | Packet IO Communication | Application Hosting Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

The CPU-based packet generator is a built-in Linux application that generates diverse traffic streams directly within the production environment, enabling in-production network diagnostics without physically isolating routers.

A CPU-based packet generator is a Linux application that

generates a wide range of traffic streams for network diagnostics in production environments
allows direct in-production diagnosis without physically isolating routers, and
integrates with IOS XR interfaces to send packets using the Packet I/O infrastructure.

Table 1. Feature History
Feature Name	Release Information	Feature Description
CPU-Based Packet Generator	Release 25.4.1	Introduced in this release on: Fixed Systems (8010 [ASIC: A100])(select vonlyariants ) This feature is supported on: 8011-32Y8L2H2FH 8011-12G12X4Y-A/D
CPU-Based Packet Generator	Release 25.1.1	Introduced in this release on: Fixed Systems (8010 [ASIC: A100])(select variants only*) This feature is supported on Cisco 8011-4G24Y4H-I routers.
CPU-Based Packet Generator	Release 24.4.1	Introduced in this release on: Fixed Systems (8200 [ASIC: P100], 8700 [ASIC: P100, K100])(select variants only); Modular Systems (8800 [LC ASIC: P100])(select variants only) This feature is supported on: 8212-48FH-M, 8711-32FH-M, 8712-MOD-M, 88-LC1-36EH, 88-LC1-12TH24FH-E, 88-LC1-52Y8H-EM.
CPU-Based Packet Generator	Release 24.2.1	Use a CPU-based packet generator for IOS XR routers to simplify diagnostics without physically isolating routers. The feature introduces the packetgen command with different options to generate different types of packets.

Benefits

Versatile traffic crafting: Create complex nested packets, such as IPinIPinIPinIP, to test and diagnose various scenarios.
In-production diagnosis: Diagnose routers in a problem state directly, without disrupting the network setup.

Capabilities

Support for diverse packet types: The CPU-based packet generator supports ARP, TCP, UDP, GRE, MPLS, IPinIP, ICMPv4, and ICMPv6 packet types.
Corrupt or error packet generation: Can intentionally create packets with known errors for debugging, such as IPv4 packets with TTL 0, incorrect checksum, or mismatched IP option length fields.

Restrictions for CPU-based packet generators

You must follow these restrictions for CPU-based packet generators:

CPU-based packet generators are not optimized for high-speed packet processing and may not match the performance of NPU-based packet generators.
CPU-based packet generators can introduce higher CPU loads during operation, which may affect router performance.
The probe packet rate is limited to 40 kpps.

Topology of the CPU-based packet generator

The CPU-based packet generator leverages the Cisco IOS XR Packet I/O framework, which serves as a host for third-party applications on the XR platform. The Packet I/O infrastructure facilitates packet transport and manages interactions between the Linux environment and IOS XR, enabling seamless communication between processes.

Implemented as a Linux application packaged within the IOS XR platform base image, the CPU-based packet generator is distributed as part of the platform, ensuring consistent deployment and integration.

The Linux infrastructure maintains a database of all IOS XR interfaces, including bundle interfaces. The CPU-based packet generator uses this database to send a specific packet type over a chosen interface, providing flexibility for testing and diagnostics.

Figure 1. Topology of the CPU-based packet generator

Packetgen CLI options and sample commands

Use the packetgen command with the following options from the XR bash environment. You can also replay a pcap file using:

packetgen -i interface_name -pcap pcap_file

Table 2. Packetgen CLI Options
Option	Description
`-accounting`	Turn on accounting for packets. Only works if packets come back to the packet generator.
`-arp-destination-hw-address string`	ARP target hardware address (default: uses interface MAC address).
`-arp-destination-ip-address string`	ARP target IP address (default: 127.0.0.1 or ::1).
`-arp-operation uint`	ARP operation (1: request, 2: reply, 3: rarp).
`-arp-source-hw-address string`	ARP sender hardware address (default: uses interface MAC).
`-arp-source-ip-address string`	ARP sender IP address (default: uses interface IP).
`-burst int`	Number of packets to inject at a time. Use with `-sleep`.
`-count int`	Number of packets to generate.
`-data-type string`	Payload type: constant, incrementing, random (default: no payload).
`-ethernet-dmac string`	Destination MAC address (default: ff:ff:ff:ff:ff:ff).
`-ethernet-smac string`	Source MAC address (default: interface MAC address).
`-file string`	Write packets to file.
`-gre`	Enable GRE.
`-gre-checksum-present`	Enable GRE checksum present bit.
`-gre-key-present`	Enable GRE key present bit.
`-gre-over-mpls`	Enable GRE over MPLS.
`-gre-protocol uint`	Set the protocol type of the GRE payload (default: 0x0800 (IP)).
`-gre-seq-present`	Enable GRE sequence number present bit.
`-gre-version uint`	Set the GRE version number (default: 0).
`-header string`	Custom header for all packets.
`-hex`	Print hex dump of packets.
`-i string`	Interface name for packet injection.
`-icmp-code uint`	ICMP code (default: 0).
`-icmp-type uint`	ICMP type (default: 0).
`-inc-dmac`	Increment destination MAC.
`-inc-smac`	Increment source MAC.
`-inner-ethernet-dmac string`	Inner Ethernet destination MAC address (default: ff:ff:ff:ff:ff:ff).
`-inner-ethernet-smac string`	Inner Ethernet source MAC address (default: ff:ff:ff:ff:ff:ff).
`-inner-ip-checksum uint`	Inner IP checksum (default: compute automatically).
`-inner-ip-dont-fragment uint`	Set inner IP Don't Fragment flag as 1.
`-inner-ip-dst string`	Inner destination IP address (default: 127.0.0.1 or ::1).
`-inner-ip-flow-label uint`	Inner IPv6 Flow Label value (default: 0).
`-inner-ip-frag-offset uint`	Inner IP fragment offset in units of 64-bits (for example, 1 = 64 bits).
`-inner-ip-protocol string`	Inner IP protocol. Supports protocol text (TCP, UDP) and code (63 for TCP) (default: TCP).
`-inner-ip-src string`	Inner source IP address (default: 127.0.0.1 or ::1).
`-inner-ip-tos uint`	Inner IP Type Of Service (TOS) value (default: 0).
`-inner-ip-traffic-class uint`	Inner IP traffic-class value (default: 0).
`-inner-ip-ttl uint`	Inner IP time to live (TTL) (default: 64).
`-inner-ip-version int`	Inner IP version (default: 4).
`-inner-vlan-id uint`	Inner VLAN ID (default: 0).
`-inner-vlan-tpid uint`	Inner VLAN Ethernet type (default: 33024, Dot1Q).
`-inner-vlan-vpri uint`	Inner VLAN priority (default: 0).
`-ip-checksum string`	IP checksum (default: compute automatically).
`-ip-dont-fragment string`	Set IP flag: 0 → 000 (nothing set), 1 → 001 (More Fragments), 2 → 010 (Don't Fragment), 4 → 100 (reserved bit).
`-ip-dst string`	Destination IP address (default: 127.0.0.1 or ::1).
`-ip-flow-label string`	IPv6 Flow Label value (default: 0).
`-ip-frag-offset string`	Fragment offset in units of 64-bits (1 = 64 bits).
`-ip-protocol string`	IP protocol. Supports protocol text (TCP, UDP, GRE, VXLAN, ICMP, NDP) and code (default: TCP).
`-ip-src string`	Source IP address (default: interface IP).
`-ip-tos string`	IP Type Of Service value (default: 0).
`-ip-traffic-class string`	IP traffic-class value (default: 0).
`-ip-ttl string`	IP time to live (TTL) (default: 64).
`-ip-version string`	IP version. Set for accurate IP packet creation (default: 4).
`-mpls-exp string`	Comma-separated MPLS EXP (Experimental) value (default: 0).
`-mpls-label string`	Comma-separated list of MPLS labels to add to the packet, from top to bottom.
`-mpls-ttl string`	Comma-separated MPLS TTL value (default: 64).
`-ndp string`	Specify the Neighbor Discovery Protocol: `nbr-solicit` or `nbr-advt`.
`-ndp-target-address string`	NDP target address (default: for advertisement, source IP; for solicitation, destination IP).
`-pcap string`	File to replay pcap.
`-progress`	Display a progress bar.
`-seed int`	Seed for pseudo-random payload generator.
`-size int`	Size of payload.
`-sleep string`	Time duration to sleep during each burst. Use with `-burst`.
`-stdout`	Print packets to stdout.
`-tcp-dport int`	TCP destination port (default: 40000).
`-tcp-flags string`	Set TCP control flags: U (Urgent), A (Acknowledgement), P (Push), R (Reset), S (Synchronize), F (Finish).
`-tcp-sport int`	TCP source port (default: 40000).
`-udp-dport int`	UDP destination port (default: 40000).
`-udp-sport int`	UDP source port (default: 40000).
`-vlan-id uint`	VLAN ID (default: 0).
`-vlan-tpid uint`	VLAN Ethernet type (default: 33024, Dot1Q).
`-vlan-vpri uint`	VLAN priority (default: 0).
`-vxlan-udp-dport int`	UDP destination port for VXLAN (default: 4789).
`-vxlan-udp-sport int`	UDP source port for VXLAN (default: 0).
`-vxlan-vni uint`	VXLAN VNI (default: 0).

Table 3. Sample Packetgen Commands
Packet Type	Sample Command
ARP	`packetgen -i enp0s8 -ip-ttl 32 -arp-operation 1 -progress -count 10000 -inc-smac -arp-destination-ip-address 192.168.56.1`
TCP	`packetgen -i enp0s8 -ip-ttl 32 -tcp-sport 40000 -progress -count 10000 -inc-smac`
UDP	`packetgen -i enp0s8 -ip-ttl 32 -udp-sport 40000 -progress -count 10000 -inc-smac`
ICMP - PING	`packetgen -i enp0s8 -ip-ttl 32 -icmp-type 8 -progress -count 10000 -ip-dst 192.168.56.1`
GRE	`packetgen -i enp0s8 -ip-ttl 32 -gre -count 100 -inner-ip-ttl 32 -tcp-sport 3222 -progress`
IP in IP	`packetgen -i enp0s8 -count 100 -tcp-sport 3222 -progress -ip-src="1.1.1.1,2.2.2.2"`
ETHER-IP	`packetgen -i enp0s8 -ip-ttl 32 -count 100 -inner-ip-version 6 -tcp-sport 3222 -progress -inner-ethernet-smac ff:ff:ff:ff:ff:ff`
VLAN	`packetgen -i enp0s8 -ip-ttl 32 -tcp-sport 40000 -progress -count 10000 -inc-smac -vlan-id 2`
QinQ	`packetgen -i enp0s8 -ip-ttl 32 -tcp-sport 40000 -progress -count 10000 -inc-smac -vlan-id 2 -inner-vlan-id 2`
VXLAN	`packetgen -i enp0s8 -ip-ttl 32 -tcp-sport 40000 -progress -count 10000 -inc-smac -vxlan-vni 3 -vxlan-udp-sport 4444 -inner-ip-version 4 -inner-ethernet-smac ff:ff:ff:ff:ff:ff -data-type constant`
NDP	`packetgen -i enp0s8 -ip-version 6 -ndp nbr-advt -count 100 -ip-checksum 1 -progress`
MPLS	`packetgen -i enp0s8 -ip-version 4 -mpls-label 1,2,3,4,5 -tcp-sport 4556 -count 1000 -progress`

Generate packets using the CPU-based packet generator

Run the CPU-based packet generator from the IOS XR bash environment to inject packets over IOS XR interfaces for network diagnostics.

The packetgen command enables you to generate a wide range of packet types directly on a router without physically isolating it from the production network. IOS XR interfaces appear as Linux interfaces in the bash environment, allowing direct use of interface names.

Before you begin

Review the CLI options and sample commands. For details, see Packetgen CLI options and sample commands.

Follow these steps to generate packets and verify injection through the CPU-based packet generator.

Procedure

Access the bash shell on the router.

Example:

Router#bash
[ios:~]$

Run packetgen with the required options to generate packets. This example sends 50 ICMP ping requests from source address 10.0.0.1 to destination address 10.0.0.2 over interface Hu0_0_0_25.

Example:

[ios:~]$packetgen -i Hu0_0_0_25 -ip-ttl 32 -progress -count 50 -icmp-type 8 -ip-dst 10.0.0.2 -ip-src 10.0.0.1 --ethernet-smac 78:c5:51:84:48:c4 --ethernet-dmac 00:00:00:1e:ca:fc
INFO[0000] [ETH IP ICMP]
INFO[0000] Setting SRC IP to 10.0.0.1
INFO[0000] Setting DST IP to 10.0.0.2
INFO[0000] Opening Handle Hu0_0_0_25
INFO[0000] Opened Handle Hu0_0_0_25
INFO[0000] Starting Packet Injection
Sending Packets... 2% | | (1/50, 254 packet/s) [0s:0s] /* Truncated output. */

Address Age Hardware Addr State Type Interface
10.0.0.1 - 78c5.5184.48c4
Interface ARPA HundredGigE0/0/0/25
10.0.0.2 00:50:23 0000.001e.cafc Dynamic ARPA HundredGigE0/0/0/25

Source stats:
Stat Name      Port Name            Control Packet Tx.  Control Packet Rx.  Ping Reply Tx.
20.0.0.2/
Card01/Port01  Ethernet - VM - 001  51                  51                  50

Interface stats:
Input    Punt XIPC  InputQ     XIPC         PuntQ
ClientID Drop/Total Drop/Total Cur/High/Max Cur/High/Max
ipv6_icmp 0/0        0/0       0/0/1000     0/0/1000
icmp      0/50       0/0       0/15/1000    0/0/1000

Verify packet delivery by reviewing the interface statistics in the output.

The statistics confirm that 50 ICMP packets were injected and received on interface Hu0_0_0_25, verifying successful packet injection through the Packet I/O infrastructure.

The packetgen command injects specified packets over the selected IOS XR interface. Using interface statistics output, you can verify packet delivery and diagnose forwarding issues.