Hot answers tagged

15

When you configure a trunk link with the command: (config-if)#switchport mode trunk all the vlans will be allowed in the trunk link. If you want to control which VLANs are allowed in a trunk link use the following commands: (config-if)#switchport trunk allowed vlan WORD VLAN IDs of the allowed VLANs when this port is in trunking mode add add ...


14

No this isn't doing anything. When the port is in trunk mode, then any "switchport access" statements are not used. The same is true with a port in access mode with any "switchport trunk" statements. In this case, you should be able to safely remove it. The purpose for this is usually in the use of DTP (dynamic trunking protocol). So you could configure ...


9

It will be sent out all ports on the native (untagged) VLAN. If there is no native VLAN, the packet is dropped.


8

Think of each VLAN as a single switch (or switch group). VLANs work by logically partitioning a single physical infrastructure. Each port is logically connected to one of the VLANs = one of the imaginary switches. Only devices connected to the same VLAN or imaginary switch can talk to each other directly. Devices in different VLANs require a router to ...


8

VLAN hopping is when a client (unauthorized node) can add VLAN tags to its frames to enter VLANs that it's not supposed to be in or when it can generate MVRP/GVRP frames to make its port a member of additional VLANs. Either the switch adds the port to the unsecured VLAN automatically or its already been a member and the tagged frames were ignored before. ...


8

Having portfast on a inter-switch link is not the best of ideas, indeed. Switches and Bridges should take the time needed (going through listening/learning phases) to converge to a loop free L2 topology. Rapid-Spanning-Tree, Rapid-PVST (Cisco), and MST are there to speed that process up from the classic 30sec of Spanning-Tree down to like 2-5 seconds. On ...


7

The short answer is, your proposed additional fiber in the diagram will not gain you any real advantage for VLAN 3. All traffic from Packaging or Fiberglass, destined to the server in Shipping on VLAN 3, will still traverse the Core. (Presuming that you have already properly tuned your Spanning Tree settings to make the Core switch stack the root bridge.) ...


7

VLAN are introduced by the IEEE 802.1Q standard, which doesn't have this notion of standard or extended VLAN, nor made any difference between VLAN under or above 1005. This is Cisco implementation that introduce this segregation. The first Cisco implementation actually supported only VLAN up to 1001, and Cisco reserved VLAN 1002-1005 for FDDI and Token Ring....


7

I'm not understanding your exact problem because you don't provide enough detail but maybe this helps: With rare exceptions, an IP subnet is mapped to a VLAN = broadcast domain = layer-2 network on a 1:1 basis. You can run multiple IP subnets inside a single VLAN but they need a router to communicate with each other. Most often this setup doesn't make too ...


7

Strongly suggested: Configure both port-channel and its members identically (except of course for description and the channel-group and vpc bits). As long as an interface is not configured to be member of a LAG, or because LACP negotiation failed and the interface remains LACP individual [1], the configuration from the given (physical) interface applies, ...


6

Fiber is not so expensive unless you are getting fleeced. Indeed, it can be cheaper than copper cabling. It's also the right solution to long runs. Given the installation costs, it's likewise foolish to install 5e rather than 6A at this date and into the future for copper. The cost of the cable is a tiny fraction of the cost to get it installed correctly. ...


6

I understand that this is an incorrect configuration, but what was blocking traffic to the new switch? Is this part of the port channel or spanning tree or something else? Nothing was actually "blocking" the traffic to the new switch, the traffic was simply being forwarded to the wrong switch. This is normal operation of ports that are part of a LAG. The ...


6

First of all an access port is by definition can only carry one Vlan. Voice vlan is used, when if its actually a voice vlan traffic needed to be carried. so lets say both vlans 232 and 233 are Data Vlans. You have to apply like below. interface Fa3/0/1, switchport mode trunk switchport trunk allowed vlan 232,233 end Now , Trunk mode is used carry ...


6

Just to amplify on Zac’s answer: you have one subnet per vlan and vice versa. At the CCNA level, you can ignore the rare exceptions. The router on a stick has an (sub)interface in each subnet. Therefore all VLANs must be trunked to the router.


6

The problem is not the traffic from the server to the switch, but the return traffic, from the switch to the server. Since the VLAN is native, the switch will sent the traffic for this VLAN untagged, while the server expect it tagged. So this cannot work as is. You should probably use this VLAN only for PXE boot and configure your server Operating ...


5

Depending on the model - it may not support both tagged and untagged traffic on the same switchport. The GS1910 is one such model. Either tag all or tag none. Just got off the phone with Tech Support to be told what I had already figured out... Good Luck


5

I think you are confusing a couple of concepts. Looking at the last configuration section of the document you have linked: 7.2) VXLAN without CVX Configuration on VTEPs: ! vlan 100 vlan 200 ! interface Ethernet 1 switchport access vlan 100 ! interface Ethernet 2 switchport mode trunk switchport trunk allowed vlan 100,200 ! interface loopback 1 ...


5

I think you're confusing what goes on internally on the switch. How it keeps track of which ports are in which VLAN is up to the manufacturer. It's important to remember that 802.1q frames are a different format than "standard" Ethernet (802.3). Standard Ethernet frames do not have VLAN IDs. A PC or other device transmits and receives Ethernet frames (...


5

At the risk of expressing an opinion here, there is no such thing as "best practice." There are good practices, there are bad practices, and there are a lot in between. There is no best practice because there are many factors which make each situation different. In the choice you present, you might consider the ease of maintenance/modification, the ...


5

Certainly this is the usual situation for the Cisco and Avaya phones I'm familiar with, as it's usual to keep voice and data traffic separate. This is from a Cisco SPA504G phone web configuration; these facilities are available through any of the methods for configuring them, through their remote provisioning mechanisms (HTTP/TFTP etc) You see that the ...


5

A VoIP phone that chains to another device is a switch, and it negotiates a trunk between the phone and the switch. This happens with CDP or LLDP. For example, a Cisco switch interface configured as an access interface connecting to a Cisco phone will use CDP to negotiate a trunk from the access interface: interface GigabitEthernet 1/0/1 switchport mode ...


5

Before VLANs, we used to do it like this: Use separate sets of switches for each area (servers, desktops, whatever) Keep those LANs completely distinct (different IP address ranges and no wires in between) Bundle several ethernet cables with cable ties, and plug all the LANs into separate interfaces of the router, which routes between the different LANs and ...


5

The bandwidth on an interface is the bandwidth on the interface. It is possible to use multiple interfaces (up to eight) in a port channel between the switches to give you a greater aggregate bandwidth, but a single flow will still only use a single link in the channel. This will require more links between the switches, but you have not given enough ...


5

Generally, you'll want to secure VLAN membership for all ports that you don't control on both link ends. If a trunk port - or rather the link partner - can simply join any VLAN they want then an attacker can very easily penetrate each VLAN. This is called VLAN hopping. You can leave trunk ports unsecured when the link is entirely within your control - your ...


5

Most of the time, a computer is connected to an access port--not because of security, but because most computers don't need to switch VLANs. And since they don't switch, most NIC cards can't create 802.1q frames required for tagging VLANs anyway. On most enterprise-class switches, an access port will drop tagged frames as a security measure.


5

You should not disable spanning tree on trunk interfaces. In fact, STP needs to be on links between the switches, which should be the trunk interfaces. You can also leave STP enabled on the access interfaces to prevent loops if someone connects two access interfaces. Look at it this way: if the links between the switches are not running STP, and somehow ...


4

Before you can forward traffic on a VLAN, you have to create it in the switch's VLAN database. For older switches, there is a separate configuration mode for VLANs. From privileged (enable) mode type: switch# vlan database switch(vlan)# vlan 12 switch(vlan)# exit switch#


4

The switch has a built-in help function: ? xa-eng(config)# trunk 1-2 trk17 trunk Do not use any protocol to create or maintain the trunk. lacp Use IEEE 802.1ad Link Aggregation protocol. <cr>


4

Here is a description of one solution: Create 4 additional VLANs on the L2 trunk. Place the firewalls between the router and L3 switches, and use 3 VLANS to connect the inside, outside and DMZ interfaces, turning the firewalls into a HA (failover) pair. The 4th VLAN becomes the heartbeat link between the two firewalls. The default gateway for the ...


4

The issue is that the link speed of the suspended interface is not the same as the rest of the interfaces in the bundle. Your working interfaces are operating at BW 1000000 Kbit Whereas, your suspended interfaces are working at BW 100000 Kbit The most common problem for interfaces that refuse to come up to auto-1000 are damaged cables. This ...


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