Category Archives: Cisco

Default STP Behavior on Cisco Switches

Posted on January 31, 2012 by Humair

In a prior blog, Functionality of Layer 2 Switches/Bridges, I discussed the core functionality of layer 2 switches. In this blog, I hit upon the Spanning Tree Protocol (STP) used on layer 2 switches to prevent loops. As mentioned before, … Continue reading →

Posted in Cisco, Labs, Networking, Protocols, Technology | Tagged Blocking, BPDUs, bridge ID, Bridge Protocol Data Units, broadcast storm, change root bridge, Cisco, Cisco 3560, designated port, device priority, Disabled, Forwarding, layer 2, layer 2 loop, Learning, Listening, loop, MAC address, prevent layer 2 loop, prevent loop, redundancy, root bridge, root port, Spanning Tree Protocol, STP | 1 Comment

Cisco – Filtering Unwanted Packets with Standard Access Lists

Posted on January 7, 2012 by Humair

Access lists (ACLs) are basically statements that packets are compared against for the purpose of taking some action if a match occurs. After an access list is created, it can be applied to inbound or outbound traffic; in some cases … Continue reading →

Posted in Cisco, Labs, Networking | Tagged access list, access lists, acess-lists, ACL, ACLs, block host, block ip address, block packet, block traffic, Cisco, Cisco 2611, Cisco 2611 router, deny host, deny ip address, deny packet, deny traffic, extended access list, filter, filter host, filter ip address, filter packet, filter traffic, named access list, router, standard access list, standard access-lists | 1 Comment

OSPF Explained and Useful Troubleshooting Commands

Posted on January 4, 2012 by Humair

Open Shortest Path First (OSPF) is an open standard link-state routing protocol that supports multiple equal-cost routes to the same destination (four by default). OSPF constructs a shortest path tree and then updates the routing table with the best paths. … Continue reading →

Posted in Cisco, Labs, Networking, Protocols, Technology, Troubleshooting | Tagged ABRs, adjacency, area 0, Area Border Routers, AS, ASBR, Autonomous System, Autonomous System Border Router, backbone area, Backup Designated Router, BDR, Cisco, Cisco 2126XM, Cisco 2126XM router, Cisco IOS, cisco router, cost, Designated Router, Hello packets, Link State Advertisement, LSA, neighbor, Neighbors, Open Shortest Path First, OSPF, OSPF Adjacencies, OSPF area, OSPF Backup Designated Router, OSPF BDR, ospf cost, ospf database, OSPF Designated Router, OSPF Hello Packets, ospf neighbor, OSPF Neighbors, OSPF process, OSPF Router ID, ospf troubleshooting, router, Router ID, Shortest Path First, shortest path tree, SPF | 3 Comments

Setting-up DHCP with IP Helper-Address on Cisco Routers

Posted on December 29, 2011 by Humair

In a prior lab, Setting-up DHCP on Cisco Routers, I discussed how to setup a Cisco router as a DHCP server. In this lab, I use a DHCP server setup on one subnet to provide DHCP services to two different … Continue reading →

Posted in Cisco, Labs, Networking, Protocols, Technology | Tagged Cisco, Cisco 2126XM, Cisco 2126XM router, Cisco WS-C2950-24, Cisco WS-C2950-24 switch, configure DHCP, dhcp, DHCP broadcasts, dhcp configuration, Dynamic Host Configuration Protocol, ip helper, ip helper-address, Setting-up DHCP with IP Helper-Address on Cisco Routers | 1 Comment

Setting-up DHCP on Cisco Routers

Posted on December 11, 2011 by Humair

The Dynamic Host Configuration Protocol (DHCP) provides the capability to automatically allocate reusable network addresses and configuration options to hosts.

Posted in Cisco, Labs, Networking, Protocols, Technology | Tagged BOOTP, Cisco, Cisco 2126XM, Cisco 2126XM router, cisco dhcp configuration, cisco router, cisco setup dhcp, Cisco switch, Cisco WS-C2960-24TT, Cisco WS-C2960-24TT switch, dhcp, dhcp configuration, Dynamic Host Configuration Protocol, router, switch | 1 Comment

Cisco VLAN Trunking Protocol (VTP)

Posted on November 23, 2011 by Humair

VLAN Trunking Protocol (VTP) is a Cisco proprietary protocol that reduces administration in a switched network. When you configure a new VLAN on one VTP server, the VLAN is distributed through all switches in the domain. This prevents you from … Continue reading →

Posted in Cisco, Labs, Networking, Protocols, Technology | Tagged Cisco, Cisco 2960, Cisco 2960 siwtch, Client Mode, Server Mode, Transparent Mode, vlan, VLAN Trunk Protocol, VLAN Trunking Protocol, VTP, VTP client, VTP server | Leave a comment

Cisco – Spanning VLANs across Switches via Trunking

Posted on November 20, 2011 by Humair

In this lab I use two Cisco WS-C2960-24TT [IOS 12.2(25)FX] switches to demonstrate how to span VLANs across switches via 802.1q trunking. I avoid using VTP by using “VTP transparent mode”; as a result, I have to configure the VLANs … Continue reading →

Posted in Cisco, Labs, Networking, Technology | Tagged 802.1q, 802.1q encapculation, Cisco, Cisco 2960, Cisco 2960 siwtch, Cisco switch, Cisco WS-C2960-24TT, isl, isl encapsulation, trunk link, Trunking, vlan | 1 Comment

Creating a LAG between an ESXi vSwitch and a Physical Switch

Posted on October 30, 2011 by Humair

In this lab I am going to create a LAG (Link Aggregation Group) between an ESXi vSwitch and a physical switch. You can use Cisco, Force10 Dell, Juniper, or any other manufacturer for the physical switch. Depending on the switch … Continue reading →

Posted in Cisco, Force10 Networks, Labs, Networking, Technology, Virtualization and Cloud Computing, VMware | Tagged 802.3ad, 802.3ad link aggregation, Cisco, ESXi, ESXi 4.1, etherchannel, Failover, Force10 Dell, Force10 Networks, LAG, Link Aggregation Group, load balancing, NIC Teaming, physical switch, pNIC, port bundle, port channel, port group, Route Based on IP Hash, Route Based on the Originating Virtual Port ID, Use Explicit Failover Order, virtual machine, virtual port ID, virtual switch, VM, VM Network port group, VMkernel, vmNIC, vmware, VMware ESXi, vNIC, vSwitch | 8 Comments

Load Balancing with EIGRP

Posted on September 14, 2011 by Humair

RIP, RIPv2, IGRP, EIGRP and OSPF are all routing protocols that support equal cost load balancing but IGRP and EIGRP can also support unequal cost load balancing. However, unlike IGRP, EIGRP supports VLSM (Variable Length Subnet Masking). Below I use … Continue reading →

Posted in Cisco, Labs, Networking, Protocols | Tagged Cisco, Cisco 3560G, Cisco 3560G router, EIGRP, eigrp load balancing, equal cost load balancing, load balancing, router, unequal cost load balancing | 1 Comment

Setup Telnet Access on Cisco Switches

Posted on September 12, 2011 by Humair

This quick lab assumes you already have an IP address for telnet assigned on the Cisco switch. Once that is setup and you are able to ping the IP address, you can setup telnet access on the Cisco switch with … Continue reading →

Posted in Cisco, Labs, Networking | Tagged Cisco, router, setup telnet, telnet, telnet access | Leave a comment