Router for Beginers

Define Router?

A Router is a device that connects two networks - frequently over large distances. It understands one or more network protocols, such as IP or IPX. A Router accepts packets on at least two network interfaces, and forwards packets from one interface to another.

Router's may be programmed to filter out some packets, and to dynamically change the route by which packets are routed.

Router's often use different media on each interface. For instance, a router might have one Ethernet port and one ISDN port.

What is the main advantage of having an L3 switch over a router?

With an L3 switch, you get the functionality of routing and more ports for access in a single box. The only additional hardware that you do not have is WAN (serial) ports. So that's the difference; with a router you get WAN ports, L3 functionality and two or three Ethernet ports (though for some of the Cisco router models you can buy a 16-port EtherSwitch module which will give you 16 10/100 802.3 ports).

What does it mean when a Cisco router says your connection has been resent by the remote host, and what is the difference between a WAN adapter and an AC97 data fax modem? Are they the same connection?

That means the remote server/router/switch has terminated the TCP/IP session you had established. There might be various reasons for this -- ranging from timing-out to the remote host running out of too many sessions.

WAN adapter and modem both give you some means of connecting to the outside world. So functionality-wise they are the same, but what technology and operation they do is different. Also the experiences you get from both are different; WAN adapters are faster.

What is the difference between RIP, IGRP and EIGRP?

 They are different routing protocols. The main difference being RIP and IGRP are distance vector protocols; EIGRP is more of link state protocol. Then there is a difference in their operations, times (like updates, refreshes, etc.), how they keep track of routing tables, etc..

Does Cisco 805 Router support BGP or not? If yes, then which minimum IOS with version is required to support this?  
  Cisco805 does not support BGP. You need to move to a higher model of the router.

How do I connect ISDN PRI via a Cisco AS5350 to a VPN server? PRI on one side and IP on the other?  
  As far as physical connectivity is concerned you need to match interface and, based up on the termination given by Telco and the interface on your CPE, you may need to use an interface converter. Once it is through, you can assign this PRI interface an IP address.

How do I to route all the calls from the phone to the POTS?

On the switch, you need to see if you are using that port for voice only or for voice as well as data. For voice only you need to create a voice VLAN on the switch and port such ports (which have IP phones) into that VLAN. For voice as well as data you need to configure default priority for untagged frames using command "switchport priority default." This will send all the data traffic to VLAN 1(default VLAN) and rest of it on voice VLAN.

What are the pros and cons associated with dynamic and static routing?

With dynamic routing there is no manual intervention and the traffic is routed automatically whenever there is any outage in the network. Also it's quite scalable/manageable. Whenever you add any more sites -- you have to add the new sites/links only. In static routing there is manual intervention every time there is any outage or addition of removal of links/sites. Management becomes quite difficult with the addition of more sites. One advantage static routing has is better control.

What is the advantage of SFP ports on a Gigabit switch? And how do I connect the four SFP ports on a D-link DGS 1248 T smart switch?

  The main advantage that I see for the SFP is the flexibility it gives you for putting it in the network. SFPs are hot-swappable input/output devices that plug into a Gigabit Ethernet port or slot, linking the port with the network. SFPs can be used and interchanged on a wide variety of products and can be interchanged in combinations of 1000BASE-SX, 1000BASE-LX/LH, 1000BASE-ZX, or 1000BASE-BX10-D/U on a port-by-port basis. You can use them for gig or fiber channel applications. They provide a flexible and cost effective solution for enterprise networks, data centers, etc.

To connect to a D-link you need to buy appropriate SFP module for the same. It should have fiber connectivity from/to remote network. These ports are sold separately which you need to buy from your local vendor.

Can a router be configured to automatically connect to the Internet even when the server is off?

A router can be programmed so that it starts a connection automatically whenever it sees interesting traffic. Interesting traffic is what an administrator (in this case, you) would define using access lists.

Until you define the traffic correctly you can avoid security breaches or some unauthorized persons accessing your connection.

How many routers can be supported within a local network?

That depends upon the reach of your network. I have seen and designed networks with 2,000+ routers. So if you can summarize routes nicely you can use that many number of routers. The most important thing is to check how fast or slow does a network converge. That should actually limit the maximum number of routers in a local network.

What is CDP in router configuration?        

CDP is Cisco Discovery Protocol, a proprietary protocol from Cisco spoken and understood by all Cisco devices. It's a Layer 2 protocol and used to check the availability of neighboring Cisco devices. It can give you all the details of the neighbors.

What is the difference between a managed and an unmanaged switch?

Managed switches have more capability than unmanaged switches. They generally offer SNMP for monitoring the status of connections, STP and other advanced features like QOS, VLAN, etc. These features may vary between manufacturers and models. Managed switches are also quite a bit more expensive. Setting them up may take a little longer as compared to unmanaged one, which is generally plug-and-play. Managed switches have remotely accessible consoles ( CLI or Web interface) and allow things such as turning ports on or off.

Which is better, a Layer 3 switch or a router in respect to WAN connection?

It is difficult to say which is better, a Layer 3 switch or a router, but for a WAN connection router is suggested. Layer 3 switches do routing but do not have serial interfaces.

What is the difference between an error and a bug?

Generally speaking, an error occurs when there is an incorrect input and is temporary in nature, whereas a bug is an unexpected flaw or imperfection that could be permanent.

How to recover  password of a router?

There are only a few methods to recover a lost password, but they all involve destroying the start-up configuration.

1. Routers that have nonvolatile RAM (NVRAM) chips can be removed and reseated. The NVRAM is implemented using battery-backed up static RAM ( SRAM). Removing the SRAM erases the contents of NVRAM, which contain the no service password-recovery configuration. Be sure to use proper anti-static procedures when handling the NVRAM. Some of these routers are 3640 and 3660.
2. Other routers, such as the 1700, 2600 and 3620, use an electrically erasable programmable read only memory (EEPROM) to hold the configuration. The EEPROM does not erase when you remove it.
3. Another method involves reloading or booting the router with console access, and pressing CTRL-BREAK within five to ten seconds of the Cisco IOS software image decompressing, or roughly when the "Image text-base:…" part of the banner begins. You are then prompted to reset the router to factory default (erase start-up configuration).

What is the difference between a payment switch and that of a router?

A payment switch is a server that creates digital representations of conventional financial instruments, and forwards authentic payment orders on these instruments to their corresponding conventional financial networks and institutions. When someone pays a credit card bill online, the payment switch would manage the processing and forwarding of that particular bill payment.

A router is a network layer hardware device that uses one or more metrics to determine the optimal path along which network traffic should be forward. Routers forward packets from one network to another based on network layer information contained in the routing table. Routing protocols accomplish routing through the implementation of a specific routing algorithm. Examples of popular routing protocols include EIGRP, OSPF and BGP. Cisco is the leading router vendor and owns 80% of the market share. Juniper is an up and coming router vendor that is giving Cisco strong competition in the router market for Service Providers.

Difference between routing and smart routing?

Intelligent routing is a method of determining the best path to send your traffic over based on real-world performance or cost of the path, as opposed to the traditional routing methods, which only select paths based on configured in policy and network topology information. This is mostly implemented in the BGP world, where normal BGP will typically select the best path based on the number of Autonomous Systems (ASes) between the BGP router and the destination, intelligent routing would test each available path for performance and then make a decision on how to route traffic based on a combination of actual performance and cost information.

Intelligent routing hasn't been implemented directly in routers at this time, and will likely stay that way. Instead it has been implemented as a separate appliance that communicates with your existing BGP speaking routers to optimize performance and cost. The cost of intelligent routing is, of course, very dependant on whom you buy it from, and whether you pay for it as an inexpensive monthly service, or a large upfront investment for hardware. Typically when purchased as a service, an enterprise can see ROI in the first month? , which is what is really important.

Is it possible to route between two subnets using a layer 3 switch ?

Yes, it is. You need to create VLANs for the subnets and route traffic (Inter-vlan routing) between them and than on the switch. A L3 switch is also a router so it understands Layer 3 routing.

What is the difference between logical segmentation and physical segmentation performed by a router?

Physical segmentation is dividing actually but in logical it?s done superficially. Say you have two links connecting to a remote location - either you can have those two links on a separate interface or you can create sub interfaces and ride both of them on a single link but have two different networks. This is logical separation. VLANs are another good example of logical separation.

what is the difference between a L3 switch and a router, and why routing through the L3 switch is faster than the router.

With current routing and switching features and power that is packed there does not remain virtually any difference between the two. Only difference is in functionally. Switches do more of switching than routing and the router does more of routing than switching. In all of the routing there is an algorithm that is run before making a routing table and routing decisions are based on that. Whereas in switching a mechanism switching table is built based on the Mac address of the source that arrives on a particular port. Flushing of the routing table is based on various factors whereas in switching tables it's merely a function of time. These factors make switching faster than routing but they both have their uses depending upon the scenario you are using.

What is the difference between the functioning of the switch and the bridge? Does the bridge pass the packet to LAN segment or to the device inside that's using its MAC address?

Bridges and switches work on same OSI layer, but the basic difference is in the functionality they provide. Basic differences would be that bridges would be used to over come limitations posed by distance and at the same time minimizing traffic. Switches will be used more from a management perspective where you can create VLANs so that you can have separate broadcast domains for your subnets.

Also bridges can be used to connect different types of media token ring to Ethernet, or token ring to FDDI.

Switches are used more from their filtering capabilities.

Bridges are strictly in Layer 2 but you get switches that can work up to Layer 3 and with modules can go up to Layer 7 with add on service modules.

Routers are typically described as 'working' at Layer 3 of the OSI model. Why would some of my textbooks describe them as actually performing tasks at layers above the Network layer?

Gone are the days when routers used to work only Layer 3 jobs. Now they do much more than -- that like filtering, server load balancing etc., which are above layer 3. That's the reason...

What does a gatekeeper router do in the context of a video teleconference implementation?

A gatekeeper is an H.323 entity on a LAN that provides address translation and control access to the LAN for H.323 terminals and gateways. The gatekeeper can provide other services to the H.323 terminals and gateways, such as bandwidth management and locating gateways. A gatekeeper maintains a registry of devices in the multimedia network. The devices register with the gatekeeper at startup and request admission to a call from the gatekeeper.

Is it possible to make a router from scratch?

making a hardware router isn't an easy thing. As it needs a lot of understanding on routing technology and how does CPUs gets interrupts and lot many other things. I can help you as far as technology is concerned. But making a chipset, designing hardware interfaces would difficult for me. I would suggest you to change your project a little bit and try to use a PC based software for routing and to see how can you use it in your project.

If you are determined, I would suggest you to go to boson.com and download their router simulator software - that would give you an idea what the final product should look like. Apart from that zebra.org is another good site. Also getting a feel of Linux would be another good idea.

Do we have standards for switches?

All vendors try to make their switches conforming to Standards. If they are not the switches will not be accepted by the market. All of the switches should conform to IEEE standards, electricity standards and environmental standards. Besides they may also have some proprietary protocols, which other vendors may not follow.