Network PC World

DNS (Domain Name System) is a crucial part of how the internet works, converting domain names into IP addresses and directing traffic. Within DNS, different types of records serve specific functions. Two key types are SRV (Service Records) and NS (Name Server Records) . SRV (Service) Records SRV records are used to define the location of specific services. These records are crucial when multiple servers can provide the same service (e.g., VoIP, messaging) and a specific server needs to be selected. They contain the following components: Service & Protocol : Defines the service (e.g., _sip , _xmpp ) and protocol ( _tcp , _udp ). Priority & Weight : Direct traffic to the most preferred server. Port & Target : Specify the server's port and hostname. Example: _sip._tcp.example.com SRV 10 60 5060 sipserver.example.com NS (Name Server) Records NS records delegate the authority for a domain to specific name servers. These name servers are responsible for answering DNS queries...

In F5 BIG-IP systems, various types of IP addresses are used, each serving a distinct role in managing traffic, routing, and device configuration. Understanding the difference between these IP types is crucial for network engineers and system administrators. Let's break down the different types of IP addresses in F5 and how they are used. 1. Self IP A Self IP is an IP address assigned to the F5 device that represents a VLAN or subnet. It enables the BIG-IP system to communicate with other devices within the same network segment. Unlike a Virtual Server IP (VIP), users or clients do not interact directly with Self IPs. Use Cases : Communication between F5 and backend servers, routers, or other F5 devices. Routing traffic within a VLAN or across multiple VLANs. SNAT (Source NAT) and clustering of F5 devices. Example : If your network uses the subnet 192.168.10.0/24 , a Self IP like 192.168.10.10 would allow the F5 to route traffic and interact with other devices in that subnet. 2. ...

The key difference between a Load Balancing Service and an Application Delivery Controller (ADC) lies in their scope of functionality: 1. Load Balancing Service : Primary Purpose : Distributes network or application traffic across multiple servers to ensure no single server becomes overwhelmed, thus improving reliability and availability. Functionality : Focuses mainly on balancing traffic using algorithms like round-robin, least connections, or IP hash. Example Features : Layer 4 (Transport Layer) or Layer 7 (Application Layer) load balancing. Simple traffic management and server health checks. 2. Application Delivery Controller (ADC) : Primary Purpose : Provides advanced traffic management, security, optimization, and acceleration services in addition to load balancing. Functionality : ADCs not only load balance but also handle application security, SSL offloading, traffic optimization, and monitoring to enhance application performance and security. Example Features : Load balancin...

In a recent lab setup using Cisco IOS XR on EVE-NG, I faced a common but frustrating issue with OSPF adjacencies getting stuck in the EXSTART state. After spending considerable time troubleshooting interface MTUs and configurations, I discovered that the root cause was related to the virtual network interface type being used. This post outlines the issue, troubleshooting steps, and the eventual solution that got everything working. Issue: While configuring OSPF between two routers running Cisco IOS XR in my lab, OSPF adjacencies were getting stuck in the EXSTART state. I verified that interface configurations, MTU settings, and OSPF parameters were correct, but the problem persisted. I tried adjusting the MTU size, using the mtu-ignore command, and even checked for ACLs, but nothing seemed to resolve the issue. Troubleshooting Steps: MTU Settings: I started by verifying that both sides of the OSPF adjacency had matching MTUs. I used the default MTU and even tried different values wit...

Cloning labs in EVE-NG is a great way to duplicate setups and expand or experiment on a new copy without affecting the original lab. However, if not done correctly, the cloned lab may only copy the topology without configurations. In this guide, I’ll show you how to properly clone a lab in EVE-NG with all configurations using the EVE-NG GUI . Follow these steps to ensure that both the topology and router configurations are retained when cloning your lab. Steps to Clone an EVE-NG Lab with Configurations Save Running Configuration on All Devices In your original lab, make sure all devices have their configurations saved to NVRAM. Go into the CLI of each router and run the command: copy running-config startup-config Export All Configurations (CFGs) On the left sidebar in the EVE-NG Web UI , click on the "More Actions" option. Then select "Export all CFGs" . This step exports the configurations of all devices in the lab. Shutdown All Devices After exporting the confi...

In this lab, we’ve set up a basic MPLS, BGP, and L3VPN environment, which is a great foundation for understanding how service providers build scalable networks. The lab uses the EVE-NG simulator along with Router IOS C7200-ADVENTERPRISEK9-M, Version 15.2(4)M8 to emulate a realistic MPLS environment. Below is a summary of the key components and roles of each router in the lab. MPLS Core Routers : The MPLS core consists of the routers responsible for label switching and forwarding customer traffic through the network: PE1 (Provider Edge 1) : Connects customer networks to the MPLS core and handles both MPLS and BGP routing. It also hosts VRF (Virtual Routing and Forwarding) instances for customers. PE2 (Provider Edge 2) : Functions similarly to PE1, connecting another customer network to the MPLS core. P1 (Core Router 1) and P2 (Core Router 2) : These routers serve as MPLS core routers and handle label switching but do not store or process customer routes directly. They simply f...

Here’s a breakdown of BGP attributes that are either considered by iBGP neighbors only or eBGP neighbors only , along with the attributes that apply to both, but may have different behaviors or implications depending on whether the neighbor is iBGP or eBGP. Attributes Considered by iBGP Neighbors Only : These attributes are shared within an AS but may not be propagated or considered by eBGP neighbors : Local Preference : Used by : iBGP Ignored by : eBGP Description : The Local Preference (Local Pref) attribute is used to influence outbound traffic within an AS. It is not sent to eBGP neighbors . An eBGP neighbor won’t see this attribute because it’s meant for internal path selection. Example : An iBGP router receiving an update with a higher Local Preference will prefer that path, but an eBGP neighbor will not receive or consider the Local Preference attribute. Next-Hop Behavior : Used by : iBGP Modified by : eBGP Description : When advertising routes to iBGP neighbors, the Next ...