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For questions about a physical or virtual interface on a network device. For instance: Interface configurations, troubleshooting and security.

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1answer
35 views

Can not create sub-interface like `interface gigabitEthernet 2/1.100`

I follow a tutorial, there shows the method of create sub-interface: but in my actual situation, I can not do this: Router(config)#interface gigabitEthernet 2/1.100 ...
4
votes
2answers
39 views

Why the Cisco Router's loopback interface can not be showed up by default?

By default, why the Cisco Router's loopback interface can not be showed up? Router#show ip interface brief Interface IP-Address OK? Method Status Protocol ...
0
votes
1answer
63 views

How does a device differentiate between a router interface and switch interface

We have a device in work, in the manual it says connect via a switch. Obviously it works fine with any other device, once it is connected via a switch. But say in a topology, it could be directly ...
0
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0answers
11 views

Input errors vs output errors - what's the difference? [duplicate]

Is there any difference between input errors and output errors in terms of determining the source of those errors? A server team complained that they had received interface errors alerts. I checked a ...
6
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3answers
1k views

How not to route on a Cisco router

So we have a router, with a switch card interface, 8 ports Say I have 4 VLANs (A,B,C,D) on it, with 2 switch ports in each. Each VLAN (i.e. all ports) can communicate with each other, because ...
-1
votes
1answer
23 views

My interface do not have a IP address in a segment, but I can ping the IPs of it

You see, in my local Mac's network interface there is no 172.18.1.*: $ ifconfig lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384 options=1203<RXCSUM,TXCSUM,TXSTATUS,SW_TIMESTAMP&...
0
votes
1answer
37 views

Network interface issues an ARP request to get the MAC address of an actively used gateway

My network interface actively uses a gateway to send IP packets to other networks. There is already an ARP entry in the cache for the IP/MAC association for the gateway. Is it normal that my network ...
1
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3answers
42 views

Interfaces named with `ge` represent what?

I see a information: Most interfaces are named according to: - Interface media type (ge, so, at, and so forth) ... I know the so represent SONET, at represnet ATM, but how about the ge ? if it ...
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2answers
76 views

Identify IP of the client causing high interface usage on uplink port

Background: We are observing a high interface load (spikes up to 1G) on a WAN (dedicated link) uplink port of a Cisco switch. How can we find the IP of the client that is causing this high load? I ...
-1
votes
3answers
190 views

Empty mac address value [closed]

Is there some MAC address value, that can be used to denote that device does not have MAC set (something like 0.0.0.0 for IP).? I thought of ff:ff:ff:ff:ff:ff, but afraid that it could be meaningful ...
2
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2answers
437 views

Network Gateways vs Interfaces

When looking at the contents of a routing table section on the Wikipedia article on Routing Tables, it contains a table as an example of a routing table with two headings which have an unclear ...
1
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2answers
86 views

Why it is neccesary to assign IP adresses to interfaces?

I know this is a very very basic doubt, but never I thought of it in a deep perspective. For example, I am going to use the following scenario: You know that we usually use a /30 mask when you are ...
3
votes
1answer
222 views

Trunk on the outside ASA interface

I have a topology as in the picture. It is designed to be a factory network. 2 ASAs in a failover cluster border the whole LAN. And it is pretty much clear how to configure them: outside interface to ...
0
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1answer
75 views

Is TCP checksum verification also offloaded to NICs? [closed]

I understand that checksum calculation at the sender side is often offloaded to the NIC. Does this also happen for verification at the receiving end?
2
votes
1answer
885 views

Subnetting and switch configuration (CISCO Packet tracer)

I'd like to ask couple questions that I have about subnetting and switch configuration (more about latter). Currently, I have subnetted my network to be on IP 192.168.10.0/29 with subnet mask 255.255....
1
vote
1answer
139 views

GNS3 wic vs slot

can any one explain the difference between WIC vs Slot? plus I want to have more L3 links in GNS3 but I cannot have more than 4 on 3725 router. there are two built in plus i can add two NM-1FE-TX in ...
4
votes
1answer
114 views

EHWIC-1GE-SFP for Cisco 1941

I was able to configure the interface but only the GE port is working, not the SFP port. Did I miss something?
2
votes
2answers
238 views

Ping loopback without interface IP address

I have two routers attached directly and both of them has loopback address. The interface has no IP address, I have just connected R1 g0/0 to R5 g0/0. If I put IP address on the g0/0 interface of both ...
1
vote
1answer
633 views

“Gateway of last resort is not set” even though I have a default route to a tunnel interface

I work with Cisco CSRs. On all of my previous CSRs in AWS, I have the following: AWS-ENV-CSR-R1#sh run | in ip route ip route 0.0.0.0 0.0.0.0 Tunnel1 ip route 0.0.0.0 0.0.0.0 Tunnel2 2 AWS-ENV-CSR-...
0
votes
2answers
59 views

Physical / Virtual Interfaces.

Well, I know that's a simple question for the level of this forum, but yet, I didn't found anything on Google, at least not what I want. I'm studying for CCNA R&S and I just learned about ...
2
votes
1answer
119 views

Can I curl a Cisco sg300 switch to get running config, MAC address table, int des, etc.?

I'm auditing switch interface descriptions at work. I work nights and sometimes people during the day shut down their computers when they leave, so I don't see which computers are on interfaces when I'...
0
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2answers
41 views

What are parts of interface name called

Consider this interface name GigabitEthernet1/0/48 I know that GigabitEthernet is an interface type. What does 1, 0 and 48 stand for?
2
votes
2answers
725 views

Aruba OS equivalent for default interface

I need to reset or default an interface on an Aruba switch. This may be the same for HP procurve switches, but I am not sure. On Cisco, the command would be default interface in global config mode. Is ...
4
votes
2answers
158 views

Inter-vlan routing with unmanaged switch?

I have a Cisco 3650 with inter-vlan routing enabled. All vlans reach each other with no problems. The problem appeared when I connected an unmanaged switch to an interface on the cisco. I set up a ...
0
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2answers
657 views

Address of the router interface in subnetting [closed]

I've been given a Class C address, let's say 192.10.20.0. I have a topology of 4 routers, each with a serial connection to two of the other routers (like a square). To each router is connected two ...
5
votes
2answers
163 views

Can a broadcast storm do physical damage to computers and networking hardware?

We had a broadcast storm that went undiagnosed for several hours. After the problem switch was unplugged and traffic returned to normal, we had a handful of machines and switches that were broken. On ...
1
vote
1answer
454 views

Cisco 2811: VLANs, Subinterfaces, HWIC-4ESW

I asked a question not too many hours ago about multiple router interfaces on one network, and I think I have now established what I need to do, however I do not understand how to implement it. For ...
1
vote
2answers
137 views

Cisco: Two interfaces on one network

I'm a newbie to Cisco Equipment and IOS, but got myself a Cisco 2811 and have been playing with it and getting to grips with the basics quite happily. One problem i'm having is trying to get two ...
2
votes
2answers
137 views

Manually set combo interface for RJ45 Cisco 3560-CG Series

I have a Cisco Catalyst 3560-CG that has two combo ports with SFP and RJ45 each. Is it possible to manually set the combo port to use the RJ45 only? If so, how is it done? I am troubleshooting a ...
0
votes
1answer
32 views

How to know which IPv6 interface will be chosen by the router?

I would like to know how does the kernel decide through which interface it sends data to some IPv6 address, how is the calculation done based on the routing table information: destination, gateway and ...
0
votes
1answer
43 views

How to assign IPs in server interfaces when connected to two similar routers [closed]

I need to connect two similar routers with the IPs 192.160.2.4/24 and 192.160.2.6/24 (in the same 192.160.2.0/24 network) to 2 server interfaces (ports) in the same server as shown in the image. ...
2
votes
3answers
239 views

Cisco C3560CX Interface number/name question

The Cisco C3560CX's come in flavors that include 10gbs SFP+ ports (e.g. WS-C3560CX-12PD-S), and also less expensive ones that only do 1gbs SFP (e.g. WS-C3560CX-12TC-S). Documentation shows you can put ...
2
votes
2answers
634 views

Cisco 3560 interface counters, are the counters reset automatically?

I have a Cisco 3560G switch. Are the interface counters reset automatically, recalculated in a specific interval (5 minutes?), or not at all? I want to get (hourly, daily, monthly, etc) interface ...
0
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2answers
180 views

Physical interface as switch port and VLAN interface as layer 3 [closed]

In most of large ISP networks, physical interfaces are used as switch ports (layer 2 port) and VLAN interfaces are used as layer 3. Could you please explain what is the main purpose to use like this?
1
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0answers
302 views

Interface is up, but wan interface ip not pinging?

I have Juniper ACX-2200 router , i have assigned an ip address to the vlan tagged to ge-0/1/2 interface , and interface status is up, but self wan interface ip not pinging , ip won't even show up in ...
1
vote
2answers
112 views

What does it mean if an Ethernet Card has two RJ45 ports?

Ethernet is below IP in the OSI model. But how is an IP address actually assigned to an Ethernet port? I know, that Ethernet has nothing to do with IP, but under Windows I can assign an IP address ...
1
vote
1answer
545 views

ARP requests and multiple interfaces

Suppose a device has both ethernet and wireless interfaces enabled and active. Is it correct that ARP requests from one (e.g., ethernet) cannot reach the other (e.g., wireless) unless a Proxy ARP is ...
0
votes
1answer
70 views

what type of fiber SFP for cisco 6500 Gbic module

I have an old 6500 with 6516a GBIC module (picture) and im planning to do some testing with it. I've already looked over Cisco's product page, and im still having a hard time identifying what SFP ...
1
vote
2answers
2k views

What are “Excess Defer Frames” on a show interface gix/x/x controller output?

I have a switch that is counting "output errors". A "show interface gi1/0/46 controller" shows up "2963657 Excess Defer frames" but I really can't find any documentation about "excess defer frames". ...
1
vote
1answer
397 views

Diifference between sfp/sfp+ ports and unified ports

there is something I don't understand. Some switches have SFP ports, it means that you can connect fiber or rj-45 cables I believe? Some switches like Nexus 5600 have unified ports. So they can ...
1
vote
1answer
2k views

Issues trunking VLANs from pfSense to Cisco switch

I am currently using an old desktop with a dual port PCI NIC as a pfSense router. Interface em0 is assigned to the WAN interface, and em1 is assigned to the LAN interface, as well as 3 VLAN interfaces ...
1
vote
1answer
504 views

TACACS: multiple source interfaces

I have a Cisco router connected to a TACACS server via two interfaces. As a prerrequisite, no loopback should be set on the router. My question is: Is it possible to set these two interfaces as ...
0
votes
1answer
268 views

VLAN trunk between Single Port Machine to Switch

i have this setup which is a bit low end because i ran out of test server to test so i'm just doing what i can to attain target setup. Normally i would use a blade or rack type server. So my setup ...
0
votes
1answer
832 views

debugging arp requests over vlan

We have a chain of switches configured for vlan 13, let's call them switch1, switch2 and switch3 No, somewhere on this chain the arp requests get lost. I can run tcpdump on these switches. Running ...
1
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2answers
293 views

Command for showing unused ports over time on Cisco switches

I was looking at a previous question about this where a command was given to look for all ports that had not been used in 6 weeks. I ran the command but it doesn't give the port names just the line ...
0
votes
1answer
97 views

Clustered Juniper devices using public DoD IP addresses for communication?

Ok, so I have to admit I am not an expert in how Juniper networked devices work, so this entire issue might be why I am having issues understanding something I am seeing on a pair of clustered SRX210H'...
1
vote
3answers
292 views

Arista switches- Email alert if interface status changes

I'm looking to be notified of interface state changes on my Arista switches without my manual polling of the logs. For example, tailing var/log/messages, I might see something like: un 29 19:10:48 ...
4
votes
5answers
2k views

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

When assigning an IP address to an interface, why do I need to specify a subnet mask? I understand the purpose of subnet masks in a routing table for example (to specify a range of IP addresses as ...
1
vote
2answers
863 views

What are the most common scenarios in which the 'loopback interface' on a router is used?

I was studying about CISCO routers and we learned that every router has a LOOPBACK interface. How and when are those interfaces used? We never used it though in our configurations.
0
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1answer
481 views

admin state Vs link state from a network engineer stand point

On a network switch, if the admin state is made "UP" by using a "no shutdown" on that physical interface then it remains "UP" what so ever until the port is configured as "shutdown". This is the ...