Cisco Port Security Violation Modes: Protect mode vs Shutdown Vs Restrict

 

🔐 Understanding Cisco Port Security Violation Modes: A Practical Guide for Network Admins

When it comes to securing your network at the access layer, Cisco Port Security is a powerful first line of defense. But what really makes it effective is how it handles violations—when an unauthorized device tries to connect. Cisco offers three distinct violation modes, each with its own behavior and use case.

Let’s break them down in a way that’s both clear and practical.

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🚫 1. Protect Mode – Silent Defender

• What it does: Silently drops packets from unknown MAC addresses.
• What it doesn’t do: No alerts, no logs, no counters.
• Port status: Remains active.
• Best for: Environments where you want to block unauthorized access without drawing attention or triggering alerts.

Think of it as a bouncer who quietly turns away uninvited guests without making a scene.

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⚠️ 2. Restrict Mode – The Watchful Gatekeeper

• What it does: Drops unauthorized traffic and logs the event.
• Extras: Increments the violation counter and can send SNMP traps.
• Port status: Remains active.
• Best for: Admins who want visibility into violations without disrupting service.

This mode is like a security guard who not only stops intruders but also files a report and notifies the control room.

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🔒 3. Shutdown Mode – The Nuclear Option

• What it does: Drops the traffic and disables the port by putting it into an err-disabled state.
• Extras: Logs the violation and can trigger SNMP alerts.
• Port status: Goes down until manually or automatically re-enabled.
• Best for: High-security environments where any unauthorized access attempt must be treated as a serious threat.

Imagine a vault that locks itself down completely at the first sign of tampering.

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🧠 Pro Tip: Choosing the Right Mode

Mode	Drops Traffic	Logs Violation	Disables Port
Protect	✅	❌	❌
Restrict	✅	✅	❌
Shutdown	✅	✅	✅

Choose Protect for silent enforcement, Restrict for visibility, and Shutdown for maximum security.

SNMP V1 vs SNMP V2 Vs SNMP V3

🔐 Understanding SNMP Versions: A Quick Guide to Network Monitoring Security

In the world of network management, SNMP (Simple Network Management Protocol) plays a pivotal role in monitoring and managing devices across enterprise networks. Over the years, SNMP has evolved through multiple versions, each improving upon the last in terms of security, efficiency, and functionality.

Let’s break down the key differences between SNMPv1, SNMPv2c, and SNMPv3, focusing on their security features and data retrieval capabilities.

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📘 SNMPv1 – The Foundation

• Security: Basic and minimal. SNMPv1 uses community strings for authentication, which are transmitted in plaintext. This makes it vulnerable to interception and unauthorized access.
• Bulk Retrieval: ❌ Not supported. Data must be retrieved one object at a time, which can be inefficient for large-scale monitoring.

🧠 Best suited for small, isolated networks where security is not a primary concern.

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📗 SNMPv2c – A Step Forward

• Security: Still relies on plaintext community strings, offering no real improvement in authentication or encryption.
• Bulk Retrieval: ✅ Introduced bulk data retrieval, allowing multiple pieces of information to be fetched in a single request. This significantly reduces network overhead.

🧠 Ideal for performance-focused environments where security is managed through other means.

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📘 SNMPv3 – The Secure Standard

• Security: A major leap forward. SNMPv3 supports:
• Authentication (verifying the identity of the sender)
• Encryption (protecting data in transit)
• Message integrity (ensuring data hasn’t been tampered with)
• Bulk Retrieval: ✅ Fully supported, combining efficiency with robust security.

🧠 Recommended for modern enterprise networks where data protection and compliance are critical.

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🧾 Summary Table

SNMP Version	Security Level	Bulk Retrieval
SNMPv1	Plaintext community strings	❌ No
SNMPv2c	Plaintext community strings	✅ Yes
SNMPv3	Authentication, encryption, and integrity checks	✅ Yes

 

Core SNMP Operations Explained

 

Simple Network Management Protocol (SNMP) enables centralized monitoring and control of networked devices. It uses a set of well-defined operations to exchange management data between SNMP managers and agents.

1. GET Request

Used to retrieve specific data from a managed device. It queries a particular object identifier (OID) to check the current status or configuration.

2. GET-NEXT Request

This operation fetches the next sequential object in the MIB (Management Information Base). It's essential for walking through tables or lists of data without knowing all the OIDs in advance.

3. GET-BULK Request

Introduced in SNMPv2, this operation is optimized for retrieving large volumes of data efficiently. It minimizes the number of requests needed to gather multiple values, especially from tables.

4. SET Request

Allows the SNMP manager to modify the value of a managed object on the agent. This is used for configuration changes, such as enabling or disabling interfaces.

5. TRAP Notification

An unsolicited alert sent from the agent to the manager when a predefined event occurs (e.g., device reboot, link failure). It’s a one-way message and doesn’t require acknowledgment.

6. INFORM Notification

Similar to a TRAP, but with a key difference: it requires acknowledgment from the manager. This ensures the alert was received, making it more reliable for critical notifications.

7. REPORT Message

Exclusive to SNMPv3, this operation is used for diagnostic and error reporting between SNMP entities. It helps troubleshoot issues like authentication failures or unsupported features.

 

Cisco IOS XR - Important Information

 

Cisco IOS XR Q&A Summary

Question 1

How many line card slots does the Cisco 8812 router have, including RP slots, and how many RU of space does it occupy?

Correct Answer: The Cisco 8812 router has 12 slots in total (including RP slots) and occupies 21 RU of space.

Explanation: The Cisco 8812 is a modular router with 12 slots for line cards and route processors. It is designed for high-performance networking and occupies 21 rack units (RU) in a standard equipment rack.

Question 2

Which two general types of deployment exist for the Cisco IOS XRd router? (Choose two.)

Options:

·       - Cisco IOS XRd Router

·       - Cisco IOS XRd Control Plane

·       - Cisco IOS XRd PCE

·       - Cisco IOS XRd Route Reflector

·       - Cisco IOS XRd vRouter

Correct Answers: Cisco IOS XRd Control Plane, Cisco IOS XRd vRouter

Explanation: Cisco IOS XRd supports two main deployment models: Control Plane (for route reflector and PCE use cases) and vRouter (includes control plane and virtual forwarder for full routing and forwarding capabilities).

Question 3

Into which three planes is Cisco IOS XR Software partitioned? (Choose three.)

Options:

·       - Control

·       - Admin

·       - Process

·       - Data

·       - Management

Correct Answers: Control, Data, Management

Explanation: Cisco IOS XR is partitioned into Control Plane (routing protocols), Data Plane (packet forwarding), and Management Plane (configuration and monitoring).

Question 4

Which three of the following user groups are typically predefined in Cisco IOS XR? (Choose three.)

Options:

·       - root-system

·       - root-lr

·       - admins

·       - cisco-support

·       - configurator

Correct Answers: root-system, root-lr, cisco-support

Explanation: Predefined user groups in IOS XR include root-system (full admin), root-lr (local route control), and cisco-support (diagnostics).

Question 5

Which command allows you to check Task permissions assigned to the user that is currently logged in?

Options:

·       - show users

·       - show tasks

·       - show user tasks

·       - show permissions

Correct Answer: show user tasks

Explanation: The 'show user tasks' command displays task permissions for the current user in IOS XR.

Question 6

Which command displays the difference between target and running configuration?

Options:

·       - show configuration

·       - show configuration running-config

·       - show configuration commit changes

·       - show configuration changes

Correct Answer: show configuration changes

Explanation: This command shows the differences between the target configuration and the running configuration in IOS XR.

Question 7

What routing protocol session is required between two PEs to exchange VPNv4 routes?

Options:

·       - external BGP

·       - OSPF

·       - IS-IS

·       - MP-IBGP

Correct Answer: MP-IBGP

Explanation: MP-IBGP (Multiprotocol IBGP) is used between PE routers to exchange VPNv4 routes in MPLS Layer 3 VPNs.

Question 8

What is the generic name of the protocol running between a CE device and the service provider's MPLS network?

Options:

·       - CE protocol

·       - PE-CE protocol

·       - VRF

·       - OSPFv3

Correct Answer: PE-CE protocol

Explanation: The PE-CE protocol refers to the routing protocol used between the Provider Edge and Customer Edge routers, which can be static, BGP, OSPF, etc.

Question 9

In MPLS networks, which device type does the service provider typically not own?

Options:

·       - CE

·       - PE

·       - P

·       - RR

Correct Answer: CE

Explanation: The CE (Customer Edge) router is typically owned and managed by the customer, not the service provider.

Question 10

Which three software packaging formats does Cisco IOS XR support? (Choose three.)

Options:

·       - .iso

·       - .bin

·       - .rpm

·       - .tar

·       - .exe

Correct Answers: .iso, .rpm, .tar

Explanation: Cisco IOS XR supports .iso (installation), .rpm (modular packages), and .tar (bundled files). .bin and .exe are not used in IOS XR.

Question 11

How do you perform software downgrade on Cisco IOS XR?

Options:

·       - With the install downgrade command.

·       - By installing the software package with the argument downgrade.

·       - By installing and activating an older software version.

·       - By rebooting the Admin VM with an argument downgrade.

Correct Answer: By installing and activating an older software version.

Explanation: Downgrading in IOS XR is done by installing and activating an older version of the software using standard install commands.

Question 12

Which command should you use to check Cisco-certified upgrade and downgrade paths on Cisco IOS XR software?

Options:

·       - show upgrade-matrix

·       - show upgrade paths

·       - show install upgrade-matrix running

·       - show install software

Correct Answer: show install upgrade-matrix running

Explanation: This command displays the certified upgrade and downgrade paths for the currently running IOS XR version.

Cisco nexus Switches( Cisco NX-OS) vs Cisco Catalyst Switches (Cisco IOS XE)

 When building a network, selecting the right switch platform is crucial. Cisco offers two powerful families—Nexus and Catalyst—each optimized for different use cases. Here's a side-by-side breakdown to help you understand which suits your environment best:

Feature	Cisco Nexus (NX-OS)	Cisco Catalyst (IOS XE)
Best Suited For	Data centers where performance, scale, and speed are critical	Campus and enterprise networks with large user bases and access layer needs
Network Scale	Fewer, more powerful switches per fabric	Many distributed switches across multiple floors or buildings
Performance Profile	High-speed packet processing with minimal latency	Balanced throughput with cost-effective performance
Buffer Capacity	Large buffers to handle bursty traffic and prevent packet drops	Optimized buffers for typical end-user traffic patterns
Interface Preference	Fiber-first: 25G, 40G, 100G via SFP+/QSFP+ ports	Copper-focused: Gigabit/10G via RJ45 ports
Storage Integration	Designed with native support for FCoE and Fibre Channel	Primarily LAN-focused, not intended for storage networking
PoE & Wireless	No Power over Ethernet or wireless support	Full support for PoE/PoE+ and integrated wireless controllers
Redundancy & High Availability	vPC (Virtual Port Channel) allows dual-active uplinks with no STP loops	StackWise/StackWise Virtual enables seamless switch stacking and redundancy

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🧠 Key Insight

• Choose Nexus if you’re building a high-performance, latency-sensitive data center with storage requirements and fast uplinks.

• Go for Catalyst if your goal is to support workforce connectivity, wireless access, and PoE devices in an enterprise environment.

What is floating static route

 A floating static route is a static route with a higher administrative distance than the primary route, so it only takes over if the primary route becomes unavailable.

Example

ip route 10.10.10.0 255.255.255.0 192.168.2.1 200

The standard order of accessing modes on a Cisco device

 

The standard order of accessing modes on a Cisco device (like a router or switch) running IOS or IOS XE is:

✅ User EXEC mode → Privileged EXEC mode → Global Configuration mode → Specific Configuration modes

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📘 Detailed Order:

1. User EXEC Mode (>)
• Access level: Basic
• Prompt: Router>
• Limited commands (e.g., ping, show version)
• Entry point when you first log in
2. Privileged EXEC Mode (#)
• Access level: Elevated
• Prompt: Router#
• Accessed using: enable
• Allows full monitoring and some configuration
3. Global Configuration Mode ((config)#)
• Prompt: Router(config)#
• Accessed using: configure terminal
• Allows device-wide configuration changes
4. Specific Configuration Modes
• Examples:
• Interface mode: Router(config-if)#
• Line mode: Router(config-line)#
• Router protocol mode: Router(config-router)#
• Accessed by entering sub-configuration commands from global config

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✅ Summary of Command Flow:

plaintext

CopyEdit

User EXEC Mode        →       enable

   Router>                   ─────────►   Router#

                                      Privileged EXEC Mode

 

Privileged EXEC Mode  →   configure terminal

   Router#                   ─────────►   Router(config)#

                                      Global Configuration Mode

 

Global Config Mode    →   interface Gig1/0

   Router(config)#            ─────────►   Router(config-if)#

                                      Specific Config Mode

Cisco IOS XE Devices - Switches Catalyst 9200 vs 9300 vs 9400 vs 9500 vs 9600 - Routers 8200 vs 8200L vs 8300 vs 8500

 

Switches

Router

Create a Match-All Contract in Cisco ACI (via GUI)

Creating a "match all" contract in Cisco ACI means defining a contract that allows all traffic types (all protocols, all ports) between EPGs (Endpoint Groups). This is often used in lab environments or for initial testing, but should be used with caution in production due to its permissiveness.

🔧 Steps to Create a Match-All Contract in Cisco ACI (via GUI):

1. Log in to the APIC GUI.
2. Navigate to:
3. Tenants > [Your Tenant] > Contracts
4. Right-click on Contracts > Create Contract.
• Name: e.g., match_all_contract
• Scope: Tenant (or as per your requirement)
• Click Next.
5. Add a Subject:
• Name: e.g., match_all_subject
• Filter: Click + to add a filter.
6. Create a New Filter:
• Name: e.g., match_all_filter
• Click + to add a filter entry.
7. Add Filter Entry:
• Entry Name: e.g., allow_all
• EtherType: ip
• Protocol: unspecified
• Source Port: unspecified
• Destination Port: unspecified
• Apply Both Directions: ✅ (checked)
• Click OK, then Finish.
8. Associate the Contract:
• Go to the EPG that should provide the contract.
• Under Provided Contracts, add match_all_contract.
• Go to the EPG that should consume the contract.
• Under Consumed Contracts, add match_all_contract.

 

Overview of BGP Aggregation

BGP route aggregation is a powerful feature that helps reduce the size of routing tables by summarizing multiple specific routes into a single, broader route. This is especially useful in large-scale networks where route optimization and scalability are critical.

In Cisco IOS, the aggregate-address command provides flexible options to control how and when summary routes are advertised. Whether you're looking to advertise only the summary, retain specific routes, or apply custom attributes, this command gives you granular control over BGP route announcements.

By default, when you use the aggregate-address command, the router advertises both the aggregate route and the more specific routes that fall under it

Let’s dive in and understand how each option can be used to fine-tune your BGP advertisements.

  1. as-set

• Purpose: Includes the AS numbers of the contributing routes in the AS path of the aggregate.
• Use Case: When you want to preserve AS path information for loop prevention or policy decisions.
• Effect: The aggregate route will have an AS_SET attribute, which is a list of AS numbers from the contributing routes.

2. summary-only

• Purpose: Suppresses the advertisement of the more specific routes.
• Use Case: When you want to advertise only the summarized route and hide the specifics.
• Effect: Only the aggregate route is advertised; specific routes are not sent to BGP peers.

3. suppress-map <map-name>

• Purpose: Selectively suppress specific routes from being advertised.
• Use Case: When you want to suppress some specific prefixes but still advertise others along with the aggregate.
• Effect: Routes matching the route-map are suppressed; others are advertised.

4. advertise-map <map-name>

• Purpose: Controls which specific routes are used to generate the aggregate.
• Use Case: When you want the aggregate to be created only if certain routes exist.
• Effect: Aggregate is advertised only if routes matching the map are present in the BGP table.

5. attribute-map <map-name>

• Purpose: Applies specific BGP attributes to the aggregate route.
• Use Case: When you want to set attributes like MED, community, or local preference on the aggregate.
• Effect: The aggregate route inherits attributes defined in the route-map.

 

Cisco ACI – Port Channel (eth1/4 & eth1/5) Trunk Configuration for VLAN 420

 

Cisco ACI – Port Channel (eth1/4 & eth1/5) Trunk Configuration for VLAN 420 – Complete Guide

In modern data center architectures, Cisco ACI (Application Centric Infrastructure) plays a vital role in automating and simplifying complex network configurations. One such common scenario is setting up a Port Channel trunk to carry specific VLAN traffic—like VLAN 420—across fabric leaf switches. This step-by-step guide walks you through the complete configuration of a Port Channel using interface eth1/4 and eth1/5 on Leaf 101, allowing VLANs 400–500, and deploying VLAN 420 in production.

Note - Multivlan on Same port on same switch in same EPG is not supported.

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✅ Objective

Configure a Port Channel (eth1/4 & eth1/5) on Leaf 101 in trunk mode to carry VLAN 420, using a static EPG binding, and associate it with the necessary ACI components like VLAN Pool, Physical Domain, AAEP, Bridge Domain, EPG, and Contract.

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✅ Prerequisites

• Cisco ACI Fabric running with APIC access.

• Leaf 101 is discovered and operational.

• End host (e.g., server or hypervisor) connected to eth1/4 and eth1/5.

• Basic understanding of ACI policies and constructs.

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✅ Step-by-Step Summary

Step	Task	Navigation Path
1	Create VLAN Pool (400–500, static)	Fabric > Access Policies > Pools > VLAN
2	Create Physical Domain linked to VLAN Pool	Fabric > Access Policies > Physical and External Domains > Physical Domains
3	Create Interface Policies (Link Level, CDP, LLDP)	Fabric > Access Policies > Policies > Interface
4	Create AAEP and associate Physical Domain	Fabric > Access Policies > Policies > Global > Attachable Access Entity Profiles
5	Create Leaf Port Channel Policy Group	Fabric > Access Policies > Interfaces > Leaf Interfaces > Policy Groups > Port Channel
6	Create Leaf Interface Profile and assign eth1/4 & eth1/5	Fabric > Access Policies > Interfaces > Leaf Interfaces > Profiles
7	Create Leaf Switch Profile and assign Node 101 and Interface Profile	Fabric > Access Policies > Switches > Leaf Switch Profiles
8	Create Tenant, VRF, and Bridge Domain	Tenants
9	Create Application Profile and EPG	Tenants > Tenant Name > Application Profiles
10	Deploy Static EPG on Port Channel (Trunk mode, VLAN 420)	Tenants > Tenant Name > Application Profile > EPG > Static Ports
11	Associate EPG with Physical Domain	Tenants > Tenant Name > Application Profile > EPG > Domains
12	Create Contract, add Subject, Filters, and associate with EPG	Tenants > Tenant > Contracts & Application Profile > EPG > Contracts
13	Associate Contract with EPG	Tenants > Tenant > Contracts & Application Profile > EPG

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✅ Step 1 – Create VLAN Pool (VLANs 400–500)

• Path: Fabric > Access Policies > Pools > VLAN
• Action:
• Right-click on "VLAN" > Create VLAN Pool
• Name: VLANPool-400-500
• Allocation Mode: Static Allocation
• Add Encap Block:
• From: 400
• To: 500
• Allocation Type: Static
• Click OK > Submit

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✅ Step 2 – Create Physical Domain

• Path: Fabric > Access Policies > Physical and External Domains > Physical Domains
• Action:
• Right-click Physical Domains > Create Physical Domain
• Name: physDom-400-500
• Associate VLAN Pool: VLANPool-400-500
• Click Submit

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✅ Step 3 – Create Interface Policies

• Path: Fabric > Access Policies > Policies > Interface
• Create: Whatever parameters you want to set on the interface
• Link Level Policy: 10G-Auto
• CDP Policy: CDP-Enabled
• LLDP Policy: LLDP-Enabled
• Portchannel: PCP_101_1_4_1_5

Ø  Mode: LACP Active

Ø  Click Submit

 

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✅ Step 4 – Create AAEP

• Path: Fabric > Access Policies > Policies > Global > Attachable Access Entity Profiles
• Action:
• Right-click Attachable Access Entity Profiles > Create AAEP
• Name: AAEP_400-500
• Click+ under Domain and Associate Domain: physDom-400-500
• Click Update > Next > Finish

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✅ Step 5 – Create Leaf Port Channel Policy Group

• Path: Fabric > Access Policies > Interfaces > Leaf Interfaces > Policy Groups > PC Interface
• Action:
• Right-click PC Interface > Create PC Interface Policy Group
• Name: PCPG_101_1_4_and_1_5
• Interface Type: PC (Port Channel)
• Policies:
• Link Level: 10G-Auto
• CDP: CDP-Enabled
• LLDP: LLDP-Enabled
• Portchannel: PCP_101_1_4_1_5
• AAEP: AAEP_400-500
• Click Next - > Finish

⚠️ Note: VLAN Trunking is controlled through Static Binding and Domain VLAN Range, not inside the PC Policy Group.

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✅ Step 6 – Create Leaf Interface Profile

• Path: Fabric > Access Policies > Interfaces > Leaf Interfaces > Profiles
• Action:
• Right Click on Profiles and Create Leaf Interface Profile: Leaf101_IntProf_PC
• Add Interface Selector: Click + under Interface Selectors
• Name: PC-eth1_4-1_5
• Interface IDs: 1/4,1/5
• Interface Policy Group: PCPG-101
• Click Ok and then Submit

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✅ Step 7 – Create Leaf Switch Profile

• Path: Fabric > Access Policies > Switches > Leaf Switch >Profiles
• Right Click on Profiles and Create Leaf Profile: Leaf101-SWProf-PC
• Click + under Leaf Selectors

Ø  Name: LS101

Ø  Blocks: 101

• Click update, then Next Associate Interface Selector Profile: Leaf101-IntProf-PC
• Click Finish

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✅ Step 8 – Create Tenant, VRF, and Bridge Domain

• Path: Tenants
• Action:
• Click Add Tenants and Create Tenant: T1 and Click Submit
• Create VRF : Path Tenants->Networking->VRFs

Ø  Right click on VRFs and Create VRF: VRF-T1, uncheck “Create A Bridge Domain” and click Finish

• Create Bridge Domains : Path Tenants->Networking-> Bridge Domains

Ø  Right click on Bridge Domain > Create Bridge Domain: BD-420

Ø  Associate with VRF-T1 and Next

Ø  Click + on Subnets and Add Gateway IP: 192.168.42.1/24

• Click Ok, Next and then Finish

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✅ Step 9 – Create Application Profile and EPG

• Path: Tenants > T1 > Application Profiles
• Action:Right Click on Application Profiles
• Create Application Profile: App420 and click Submit
• Create EPG Path: Tenants > T1 > Application Profiles> App420
• Right Click on Application EPG > Create Application EPG:

Ø  Name: EPG-420

Ø  Associate with Bridge Domain: BD-420

Ø  Click Finish

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✅ Step 10 – Deploy Static EPG on Port Channel (Trunk, VLAN 420)

• Path: Tenants > T1 > App420 > EPG-420 > Application EPGs > EPG-420
• Action:
• Right-click EPG-420 > Click Deploy Static EPG on PC, VPC or Interface
• Path Type: Direct Port Channel
• Path:  PCPG-101
• Port Encap: 420
• Mode: Trunk
• Click Next>Finish

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✅ Step 11 – Associate EPG with Physical Domain

• Path: Tenants > T1 > App420 > EPG-420
• Action:
• Right Click EPG-420 and click on Add Physical Domain Association
• Domain: physDom-400-500
• Click Submit

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Step 12 – Create Contract and Associate with EPG

🔹 12.1 – Create Filter

• Path: Tenants > T1 > Contracts
• Right-click Filters > Create Filters: Filter-TCP80
• Click + under Entries
• Node: Entry_TCP80
• EtherType: IP
• IP Protocol: tcp
• Stateful: checked
• Destination Port/Range: From/To:http
• Click Update and then Submit

🔹 12.2 – Create Contract

• Path: Tenants > T1 > Contracts
• Right-click Standard > Create Contract: Contract-420
• Click + under Subject ,Name:Subject-420
• Click + under Filters
• Name: choose T1/Filter-TCP80
• Action: Permit
• Click Update and then Submit
• Click OK, then Submit

🔹 12.2 – Associate Contract with EPG

• Path: Tenants > T1 > Application Profile>App420 >Application EPG> EPG-420
• Right Click on EPG-420
• Click Add Provided Contracts
• Select: Contract-420
• Click Add, then Submit