Top posts
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Cisco IOS File System
Every Catalyst switch requires an operating system to ensure the ongoing operation of the switch, as well as ensure the configuration applied to the switch is implemented by the various hardware components. Cisco Catalyst switches include a main operating...
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VLANs, Trunk and Access ports
Let’s talk about VLANs today. Some time ago a friend of mine made me a question. If two PCs are connected to two different switches and they are in two different VLANs, however, the switches are connected to each other with access ports (each belonging...
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Cisco ospf lsa types
Type-1 LSA – It’s is the Router LSA; this is defined in order to send the link state information about the attributes of the directly connected routes, besides of that you have just ONE type-1 LSA per every router inside your area. Type-2 LSA – It’s the...
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Blocking and listening state in STP
Question: In blocking state switch ports will only listen BPDUs but not forward BPDUs. If yes then how this switch is receiving BPDUs from other switches since other switch ports will also be in "disable" state so they can not send BPDUs. I heard that...
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Is EIGRP a Hybrid Routing Protocol or Advanced Distance Vector Routing Protocol?
This question was discussed recently on the Cisco CCIE Routing and Switching Study Group website. It took me years to work out that the problem with this question is the question itself, not the answer. The question gives the impression that “Hybrid“...
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Cisco 3750X channel-misconfig
Question: I have two WS-C3750X-24T-S for stack, and i want connect a 2960 switch on this stack with port-channel. I connect 2960 G0/1 to 3750X G1/0/24, and 2960 G0/2 to 3750X G2/0/24. the config is that: 3750X: interface Port-channel1 switchport trunk...
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Details about C6509-E with the modules VS-S720-10G-C,WS-X6708-10G-3C, and WS-X6548-GE-45AF.
Question: We are building C6509-E chassis that will have dual supes with the following modules VS-S720-10G-C Does this already come with the MFSC3/PFC3C WS-X6548-GE-45AF Does this already come with the WS-F6K-AF card What is the difference between this...
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Cisco Switch Password Recovery
This tutorial documents the procedure for performing a password recovery on a Cisco WS-C2960S-24TD-L switch (and probably other models, as well). 1. Unplug the power cable. 2. Hold down the mode button while replugging the power cable. 3. Type flash_init...
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What is the difference between router and L3 switching
Question: What is the difference between router and L3 switching apart from WAN interfaces? Answer: Routers were devices that connected the LAN to the WAN and switches were just LAN devices and you may add a layer 3 switch,for example WS-C3750X-48P-S...
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Configuration Change Notification and Logging
Change notification is a nice feature on Cisco IOS devices that lets you keep track of the changes that have been made to your configuration. It can even track the user who made these changes and it can send this information to a syslog server. This is...
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Cisco Catalyst switches port-channel interface
Question: To connect two WS-C2960S-48TD-L Catalyst switch stacks, I use EtherChannel, i.e. I aggregate several ports on each switch to get more bandwidth and higher availability than with just a single port. However, the link doesn't work yet. What could...
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How can I make a PVST+ switch root towards MST network?
Question: In a network where the majority of the Cisco WS-C3750X-48P-S switches are running MST but a select few are still running PVST+, how can the PVST+ switch be configured to be the root of the spanning tree? Topology below: +--------+ +---------+...
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How can I make a PVST+ switch root towards MST network?
Question: In a network where the majority of the Cisco WS-C3750X-48P-S switches are running MST but a select few are still running PVST+, how can the PVST+ switch be configured to be the root of the spanning tree? Topology below: +--------+ +---------+...
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How to find the port a device is connected to, based on IP, on a Cisco Catalyst switch
Question: On a Cisco WS-C3750X-24S-S Catalyst switch, I need to find what port an end device is connected to. I have the IP address/host name. How do I quickly find the port? Answer: The answer depends on whether the switch is a Layer 2 or a Layer 3 switch....
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Recovering IOS on a 2600 Series
Real World Application The Cisco 2600 Series Multi-Service router platform is a dying bread as the Cisco 2800 Series has taken its place however the 2600 series continues to be the router of choice when it comes to building your own Cisco Lab. The Cisco...
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Configure ADSL on a Cisco Router
When would you need this: When you need to configure your router to operate on ADSL line provided by an ISP. Special Requirements: ADSL WAN interface on the router. Before starting, makea list of the information you will need from your service provider....
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CEF and load sharing
Load-sharing is one of the clumsy areas that is full of confusing parts. In this post we should be covering its ABCs, and latter on we should be covering more parts in details. We chose the name “CEF and load sharing” as the post name due to the main...
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Difference between arp and inverse arp
Question: So basically both arp and inverse-arp are L2 to L3 mappings; simple arp: MAC(L2) -----> IP(L3) inarp: DLCI(L2) -------> IP(L3). But by the word "inverse" I read _opposite of_ , thus implying inarp is the opposite of arp. Can someone elaborate...
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Configure DHCP on CISCO router
This post is about configuring a CISCO 2951 router to act as a DHCP server in your network. Task1: Configure R1 to act as a DHCP server and provide all network information to hosts in the LAN dynamically. (R1 and R2 are directly connected via Ethernet)...
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Cisco SYN FLOOD protection
Question: How could one mitigate SYN FLOOD DOS on Catalyst WS-C3750X-48T-L as it has no control plane protection? Answer: 3750 does have some internally priority on what it prefers to punt when congested, but it's not configurable. So you should rely...
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Intervlan Switching
Question: In Lab , I have used two Cisco WS-C3560X-24T-L Switches. I have created two vlans Vlan2 and Vlan 3 on first Switch. I have created two SVI on first switch and assign Ip address 10.10.20.1/24 and 10.10.30.1/24 respectively. Host between...
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Assigning Multiple IP Addresses to Network Interfaces
Question: Why would we configure secondary ip on an interface Suggestions please Answer: With secondary addressing, multiple IP subnets coexist in the same LAN. It's a handy tool for non-disruptively adding IP addresses to an existing LAN, without...
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Connect Cisco 3750x to Procurve 2910
Question; If the connecting port on WS-C3750X-48T-L to procurve 2910 belongs vlan 10, does the connecting port on procurve 2910 has to belong to the same vlan? Would both switches be connected if their connecting ports do not have the same vlan number?...
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NEVER use the “no exec-timeout” command!
When configuring a cisco router or switch, you may have been told that you can stop your console or telnet sessions from timing out by using the following configuration: line con 0 !(or line vty 0 4) no exec-timeout !DON'T DO THIS! NEVER issue the command...
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How to upgrade an IOS file on a 2950 or 2960 Catalyst switch?
The following tip is similar to the one on the Router IOS image transfer. It is highly recommended that you are familiar with Router IOS image transfer procedure (including the troubleshooting) before attempting Switch IOS image transfer, especially when...