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11 votes

Why do I need to specify a subnet mask on interface?

Super simple answer... It tells the computer what range of addresses it can talk to before sending the traffic to the gateway to decide where it goes next. The traffic in that range never goes to ...
Fixitrod's user avatar
  • 938
10 votes
Accepted

Why do I need to specify a subnet mask on interface?

The router uses the IP address and mask configured on an interface to determine what network is attached to that interface. That network and mask then become part of the routing table as a directly ...
Ron Maupin's user avatar
  • 99.8k
10 votes
Accepted

How not to route on a Cisco router

While Ron and Ron's answers actually enable routing but prevent traffic, their suggestions still pack both host groups into the same routing instance. There's another way to think about this: a) ...
Marc 'netztier' Luethi's user avatar
8 votes
Accepted

Which physical interface would be used to send/receive packets intended for a loopback interface?

It depends on routing table of router2 and other devices in your network (if you have any between router1 and router2). Router1 does not influence on it, it can be do something only when packet ...
Konstantin Goncharenko's user avatar
8 votes
Accepted

Switching interface VLAN ID Mid-Production

I was wondering if there was a way to switch out the VLAN ID from VLAN1 to VLAN10 without impacting the connectivity of the end users? No. First, you must remove the addressing from VLAN 1 before ...
Ron Maupin's user avatar
  • 99.8k
7 votes
Accepted

Why is Cisco enforcing X:X:X:X::X for link-local addresses when the standard says FE80:/10?

The document to which you link claims a specific IOS version. It may be incorrect; that would not be unusual in Cisco documentation. In reality, having tested this on several IOS 15.X versions, you ...
Ron Maupin's user avatar
  • 99.8k
7 votes

Why do routers have only a few interfaces?

You forget that routers can have virtual interfaces. For example, you can create GigbitEthernet0/0.10. You can have many, many different VLANs, each with its own network, on virtual interfaces of a ...
Ron Maupin's user avatar
  • 99.8k
7 votes
Accepted

What is responsible for dropping Layer 2 frames that's not addressed to it?

The details of this are highly dependent on the hardware, but your description is correct: for many years now it is normally the network interface card which discards the frames which don't match the ...
jonathanjo's user avatar
  • 16.3k
7 votes

Serial interfaces of router are used nowadays?

As Ricky Beam has already written, even though Serial connections might not be common where you live, that doesn't mean they don't exist. Over 90% of the connections we have in Europe use either ...
Cow's user avatar
  • 1,732
6 votes
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EHWIC-1GE-SFP for Cisco 1941

You can change to the SFP interface. Under the interface configuration, configure: media-type sfp To change back to the copper interface: media-type rj45
Ron Maupin's user avatar
  • 99.8k
6 votes

Why it is neccesary to assign IP adresses to interfaces?

You're right: you can have unnumbered point-to-point interfaces, for the reason you gave. Have a read of this explanation of unnumbered interfaces work in Cisco routers. We normally do number ...
jonathanjo's user avatar
  • 16.3k
6 votes
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What's the relationship of a Router with its loopback interface in logic?

Loopback interfaces are virtual interfaces that are considered directly connected interfaces. Your Loopback0 interface is defined with a /32 network, which, by definition, is a local route. How you ...
Ron Maupin's user avatar
  • 99.8k
6 votes
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What can an IP address be assigned to?

IP addresses are assigned to interfaces, either physical or virtual. For example, for a physical interface, such as a NIC, or a virtual interface, such as a loopback or SVI. Some people think IP ...
Ron Maupin's user avatar
  • 99.8k
6 votes
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Do the concepts of IP address and network interface not belong to the same layer?

Tim, you are trying very hard to map abstract concepts to real life hardware and software. They don't map exactly, so you always will have things that don't fit. Software is modularized for ease of ...
Ron Trunk's user avatar
  • 67.6k
5 votes

What is the difference between WAN and LAN ports?

A LAN is typically something completely within your own premises (your organization's campus, or building, or office suite, or your home), so it's something you build and own yourself, all the way ...
scott spencer's user avatar
5 votes

How to know the interface utilization on a Cisco switch?

What you are looking at is the bit rate over the last five minutes. You can change the time period, but not below 30 seconds with the load-interval command. I'm not sure what you mean by "utilization....
Ron Maupin's user avatar
  • 99.8k
5 votes
Accepted

What it means to configure two global ipv6 address on a single interface?

IPv6 allows, and often requires, multiple addresses on the same interface. The is more difficult in IPv4, although not always impossible. What it means is that a host configured with multiple ...
Ron Maupin's user avatar
  • 99.8k
5 votes
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Can a broadcast storm do physical damage to computers and networking hardware?

I don't think this is possible. A broadcast storm from a bridge loop will effectively bring down much/all of your network (depending on bandwidth) but doing some permanent damage to the hardware is ...
Zac67's user avatar
  • 84.8k
5 votes
Accepted

Interfaces named with `ge` represent what?

I guess you're asking about JunOS, the Operating System of Juniper for their hardware. ge means Gigabit Ethernet. This a list of ethernet interfaces and names used in JunOS: ae— Aggregated Ethernet ...
jcbermu's user avatar
  • 4,497
5 votes

How not to route on a Cisco router

You can simply create access lists to restrict traffic, and place those access lists on the VLAN interfaces. For example an ACL to prevent traffic from 10.11.12.0/24 to 10.11.13.0/24 can be created ...
Ron Maupin's user avatar
  • 99.8k
5 votes
Accepted

Urgent: how to configure different interface using same ip subnet in asa 5506?

The ASA 5506 doesn't have the switchport commands like the 5505. In routed mode, each interface is on a separate subnet, like a router.
Ron Trunk's user avatar
  • 67.6k
5 votes

How does a router know the MTU of a network?

Routers know because they have physical interfaces connected to the networks. Those interfaces are configured for the correct MTU. You are mistaken about OSPF: The protocol does not exchange MTU ...
Ron Trunk's user avatar
  • 67.6k
5 votes

Cisco ASA 5585X Internal-Data0/1 interface errors

From Cisco tech note: The ASA interface error counter "overrun" tracks the number of times that a packet was received on the network interface, but there was no available space in the interface ...
Ron Trunk's user avatar
  • 67.6k
5 votes
Accepted

What's the `line protocol` and `Link`?

For this particular interface, the line protocol is ethernet. The Link Up/Down Trap is enabled message is telling you that the SNMP trap for when the link goes up or down, for whatever reason (admin ...
Ron Maupin's user avatar
  • 99.8k
5 votes

Relationship between full duplex and speed

Full-duplex data transmission means that data can be transmitted in both directions on a signal carrier at the same time. That is incorrect. It means devices can transmit and receive at the same ...
Ron Trunk's user avatar
  • 67.6k
5 votes
Accepted

What is the relation between software and hardware ports?

There is no relation (or only a very distant one). A hardware interface attaches a network to a host (or devices like switches or router). It belongs to the physical layer (OSI layer 1). A port number ...
Zac67's user avatar
  • 84.8k
5 votes
Accepted

Unable to disable CRC check on Cisco 2960-X

The giveaway is the port name Gi1/0/50. An SFP+ DAC generally requires an SFP+ (10G) port. There are very few SFP ports (1G) that accept SFP+ modules. There are no SFP DACs, so you could use either a ...
Zac67's user avatar
  • 84.8k
5 votes

Copying IOS from TFTP problem

I was able to ping the TFTP server before I booted from it. But now the interface is down and I can't copy the .bin file to flash now. That's by design. The FastEthernet Port on the Cat4500 ...
Marc 'netztier' Luethi's user avatar

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