Cisco ISR4321 Routers – Secure, Scalable Enterprise Branch Routers

The Cisco ISR4321 Series routers deliver a compact, high-performance solution for branch offices and enterprise networks. As part of the Cisco 4000 Family of Cisco integrated routers, the ISR4321 combines wired routing, SD-WAN, security, and application services in a single platform.

Powered by Cisco IOS XE software and multicore architecture, these enterprise-grade routers support up to 100 Mbps encrypted throughput, scalable services, and flexible modularity—ideal for secure, reliable WAN connectivity and on-premises applications in small to midsize deployments.

Product Overview

Specification

Specification	Cisco ISR4321/K9
Default Aggregate Throughput	50 Mbps
Performance License Throughput	Up to 100 Mbps
Onboard GE Ports	2 × 10/100/1000 WAN/LAN (RJ-45)
SFP Ports	1 × 1 Gbps SFP
NIM Slots	2 × Network Interface Module slots
Integrated Services Card (ISC) Slot	1 × ISC slot
Service-Module (SM-X) Slots	0
Flash Memory (Default/Max)	4 GB / 8 GB
DRAM (Default/Max)	4 GB / 8 GB
CPU Architecture	Multicore x86 with distributed control, data, and services planes Cisco
Software	Cisco IOS XE 17.x
Embedded Security & SD-WAN	Cisco Catalyst SD-WAN, IPSec, NGFW (Optional via bundles)
Form Factor	1 RU rack-mountable

Competitor Comparison

Feature	Cisco ISR4321	FortiGate 60F	Juniper SRX320
IPsec VPN Throughput	Up to 100 Mbps (perf. license)	6.5 Gbps	336 Mbps
Embedded Security	NGFW, IPS, URLF, AMP (on-box)	NGFW, IPS, SD-WAN (all in hardware appliance)	NGFW, IPS, basic UTM
Modularity	2 NIM, 1 ISC slots	Fixed appliance; no modular slots	No modular expansion
SD-WAN	Cisco Catalyst SD-WAN	FortiOS SD-WAN	Juniper Secure Connect (controller-based)
Integrated Management	Cisco DNA Center, CLI, SNMP	FortiManager, FortiCloud	Juniper Mist, CLI
Form Factor	1 RU rack-mount	Desktop/appliance	Desktop

Core Features

Cisco Catalyst SD-WAN Integration
Enables policy-driven overlay tunnels, application-aware routing, and dynamic path selection across MPLS, broadband, and LTE links for optimized WAN performance.
Multicore x86 Architecture
Separates control, data, and services planes to deliver consistent performance for concurrent services without impacting routing throughput.
Embedded Security Services
Supports on-box next-generation firewall (NGFW), intrusion prevention (Snort IPS), Advanced Malware Protection (AMP), and URL filtering through optional security bundles.
Flexible Modularity
Two NIM slots and one ISC slot allow deployment of WAN interface modules (e.g., 4G/5G, PoE, T1/E1), storage modules, or UC DSP modules, with online insertion and removal (OIR).
High-Performance IPsec Acceleration
Delivers up to 100 Mbps IPsec VPN throughput (performance license) for secure site-to-site and remote-access connectivity.
Intent-Based Networking & Cisco DNA
Integrates with Cisco Digital Network Architecture (DNA) for automated provisioning, policy enforcement, and advanced analytics via Cisco DNA Center.
Trustworthy Solutions
Secure Boot, hardware root-of-trust, and Secure Unique Device Identifier (SUDI) ensure platform integrity from factory to runtime.
Zero-Touch Provisioning
Powered by Cisco Plug and Play (PnP) and Cisco DNA Center, enabling automated, hands-off deployment at scale.
Pay-As-You-Grow Licensing
Performance and feature licenses (throughput boost, security, advanced routing) can be activated on demand, protecting investment and simplifying budgeting.
Comprehensive Management
Managed via CLI, SNMP, Cisco IOS Embedded Event Manager (EEM), IP SLAs, NetFlow, and integration with Cisco Prime or DNA Center for end-to-end visibility.

Installation and Setup

Technical Guides

Site Survey & Placement

Assess WAN link types, rack space, and power availability.
Plan for module requirements (e.g., LTE, PoE, DSP) and ensure sufficient clearance for airflow and cable routing.

Core Allocation Tuning

Default splits allocate cores between control and data planes.
Use platform hardware multicore data-plane to dedicate more CPU cores to packet forwarding when running minimal services.

SD-WAN Configuration

sdwan

overlay name branch-overlay

vpn 1

exit

interface GigabitEthernet0/0/0

sdwan transport interface color biz-internet

no shutdown

Security Bundle Activation

license boot module isr4321 sec

security

ip inspect name NGFW tcp

exit

Interface Module Installation

Insert NIM or ISC modules following Cisco’s OIR procedure:

hw-module subslot 0 power off

install module NIM-4G-LTE

hw-module subslot 0 power on

Software Upgrades

Use Cisco DNA Center or request platform software package install for zero-impact rolling upgrades of IOS XE.

Performance Monitoring

Configure IP SLA probes for WAN latency and jitter.
Enable show platform hardware throughput level to monitor CEF performance.

CLI Configuration Examples

Global SD-WAN Enable

configure terminal

sdwan

exit

Create and Map Overlay

configure terminal

sdwan

overlay name branch-overlay

vpn id 1

exit

Configure WAN Interfaces

configure terminal

interface GigabitEthernet0/0/0

description Internet

sdwan transport interface color biz-internet

no shutdown

exit

interface GigabitEthernet0/0/1

description MPLS

sdwan transport interface color biz-mpls

no shutdown

exit

Apply IPsec Profile

configure terminal

crypto ikev2 proposal ike-prop

encryption aes-cbc-256

integrity sha256

group 14

exit

crypto ipsec profile ipsec-br

set ikev2 ipsec-proposal ike-prop

exit

interface Tunnel0

ip address 10.1.1.1 255.255.255.252

tunnel source GigabitEthernet0/0/0

tunnel destination 203.0.113.2

tunnel mode ipsec ipv4

tunnel protection ipsec profile ipsec-br

exit

Enable NGFW

configure terminal

license boot module isr4321 sec

security

exit

Real Case Studies and Scenarios

Retail Chain Branches
A national retailer deployed ISR4321 routers at 200 small-format stores. Zero-touch provisioning reduced rollout time by 70%, while SD-WAN delivered seamless failover between MPLS and broadband links with sub-30 ms convergence.
Healthcare Clinic Network
A multi-site clinic chain leveraged ISR4321 with security bundles to run Cisco Umbrella SIG and Snort IPS on-box. They achieved HIPAA-compliant telemedicine VPN at 80 Mbps with end-to-end encryption.
Smart Manufacturing
An automotive supplier integrated ISR4321 routers to host edge compute containers for predictive maintenance. The multicore services plane offloaded analytics workloads, reducing latency by 40% during peak data collection.

Frequently Asked Questions (FAQs)

What is the default and maximum throughput of the Cisco ISR4321?
Default is 50 Mbps, and up to 100 Mbps with a performance license.
How many WAN and LAN ports does ISR4321 have?
It offers 2× 10/100/1000 RJ-45 ports and 1× 1 Gbps SFP port.
Can I run SD-WAN on the ISR4321?
Yes—Cisco Catalyst SD-WAN is fully supported, enabling intelligent path selection and overlay management.
Which security services are available on-box?
Next-gen firewall (NGFW), Snort IPS, AMP, and URL Filtering can be activated via security bundles.
How many expansion modules can ISR4321 support?
It provides 2 NIM slots and 1 ISC slot for WAN, PoE, cellular, or DSP modules.
What software does the ISR4321 run?
Cisco IOS XE 17.x, with support for modular containers and advanced API automation.
Is zero-touch deployment supported?
Yes—integrated with Cisco DNA Center and PnP for automated provisioning at scale.

Conclusion

The Cisco ISR4321 routers deliver a versatile wired router platform for branch offices, blending enterprise-grade routing, security, and SD-WAN in a compact package.

With multicore performance, modular flexibility, and on-board security services, the ISR4321 is a cornerstone for modern, secure, and scalable branch networks. Its integration with Cisco DNA Center further simplifies management and accelerates digital transformation across distributed sites.

Did this article help you or not? Tell us on Facebook and LinkedIn . We’d love to hear from you!