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Suppose you have two NICs with the same MAC address, but not necessarily the same IP address. You can't have that within the same link-layer segment. Identical MAC addresses will disable reliable switching/bridging. What is the least possible separation (in terms of number of switches, routers, different IP subnets etc.) needed that would still allow ...


7

why not just ... a MAC address? A router might not use a MAC address on an interface - not all L2 protocols use MACs even though many do (mainly the IEEE ones like Ethernet or 802.11). Also, routers are used in network layer protocols which only have a very rough concept of data link layer topologies (if at all). Also [MAC address] should eliminate the ...


5

You can create your own MAC address. It's called a Locally Administered Address. You indicate it by setting the the second-least-significant bit of the first octet of the MAC address to 1. So, why to not create a protocol, that will automatically assign to connected devices MAC address in that way, so they don't repeat in network? Consider how you ...


5

Zac has put a great answer together. But I wanted to add a simplified answer along the same lines. Identical MAC, not within a single layer 2/broadcast domain. There are probably a lot of devices out there with the same MAC address, but because the minimum required separation is at this very low level it doesn't cause issues. Another consideration to ...


5

Unless your PC is configured as a bridge, it does not have a MAC address table. Since the PC does not forward frames from one interface to another, it has no need for a MAC table.


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The data will get lost. At the very latest, the last router in the chain will send a "Who has X" ARP request and get no answer, so it will not be able to deliver the packet. Or, if it still has the MAC address in its ARP cache, it will send the frame to a MAC address that no longer exists on the network, and the frame will just end up being ignored ...


4

OUI's are assigned. That bit is only set for assigned broadcast and multicast addresses. No organization will be given an OUI with that bit set.


3

What you're looking for is generally called "port isolation". On NX-OS, that's done with private vlans. Yes, at first glance, PVLAN configuration can be confusing, but Cisco has many documented examples. Here is one such document. (old, and ignore that it's for a 7000 and v5_x) vlan 3 private-vlan isolated vlan 2 private-vlan primary private-vlan ...


3

An IP multicast router (usually that's a switch) announces available groups using membership queries. A host subscribes to some of these groups by sending a membership report. Unsubscribing works by sending a leave group or when the subscriber doesn't refresh its membership and the router's timer kept for each host runs out (after max response time). IGMPv2 ...


3

If layer 3 interface for that specific network is configured on router then router will discover physical address of compute, Arp works as fallows When a new computer joins a LAN, it is assigned a unique IP address to use for identification and communication. When an incoming packet destined for a host machine on a particular LAN arrives at a gateway of ...


3

As I know BSSID is derived from MAC Address, but I have no idea how it is derived and what pattern is used. It is possible, but not any sort of requirement. It is simply often just easier for vendors to assign consecutive addresses from their OUI space for use in the access point. But there it is possible and even likely that there is no correlation for ...


3

You don't see the ethernet header because you are not capturing traffic on an Ethernet interface. You are using the Linux cooked-mode capture. As per this answer on StackOverflow, which itself refers to The Wireshark Wiki this mode doesn't provide the link-layer header. From the above Wiki page: When capturing from the "any" device, or from one of those ...


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Entries in an ARP table on modern OSes will time out. This is not an official part of RFC 826, An Ethernet Address Resolution Protocol, although the RFC does discuss it at the end: Related issue: It may be desirable to have table aging and/or timeouts. The implementation of these is outside the scope of this protocol. Here is a more detailed description (...


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The network in question can have multiple devices, multiple switches and no routers in between. A MAC address has only meaning within the scope of its local segment (same switch or VLAN), outside it's meaningless and there's no way to use it or find out anything about it network-wise. Reverse ARP, Dynamic Reverse ARP and Inverse ARP. The devices on ...


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After going over the existing documentation it appears that it is supported but not implemented, allow me to expand. The TRAP jnxSecAccessIfMacLimitExceeded falls under Port Security Features, hence the mac-limit would be under the secure-access-port stanza, and as per documentation, these actions differ from the interface-mac-limit packet-action; they don't ...


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You can access it via Serial port or Console cable. But you need to know username and Password. But it should be a manageable switch. Generally switch has no ip address and if it has ip address that mean it should be in device management vlan. Firstly check your device management vlan ip address range. You can find mac address using IP scanner tool. Most ...


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The problem with any multiple-access network (Ethernet, radio protocols and so on) is that even to assign an address at startup, you need be able to communicate with the device to tell it "here's your address". Now, how do you tell THAT device the communication is intended for them? Well, you need some kind of unique identifier (think DHCP which relies on ...


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Setting an IP address as a default gateway provides two things: allows the host to "find" (via ARP) the appropriate MAC address for L2 encapsulation informs the host which interface to use to find the gateway (via Routing table) Imagine a host has three network connections, each with unique IP address space. Typically, only one of those network connections ...


2

In all shared media, every host receives every frame. The host determines which are addressed for it and ignores everything else. In switched Ethernet, the switch only sends packets to the host that match its address(es), but the host still acts as if it's a shared media, i.e., it only responds to frames addressed to it.


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The internal mechanisms depend on the specific OS, but in general, the application binds a socket to a specific multicast address, just as it would for unicast. The OS then: keeps track of this -- it'll need it later sets the NIC multicast address filter sends a "JOIN" message immediately, and subsequently sends membership reports when it receives a group ...


2

Adding a few points to Stuggi's answer MAC address table is also a forwarding table, Just like a IP forwarding table at layer 3. In any forwarding table the format is entity : next hop. Hence a switch will never store its own address in the MAC address table. Becuase if it would, logically it would mean that: To reach MAC address aa:bb:cc:dd:ee:ff the ...


2

1) Yes, your table looks correct, the switch will update the MAC-address table when it receives a new frame with the source address from the frame. That way it builds the MAC table of what endpoints are connected to what interface. 2) Any switch that I've seen checked doesn't show it's own interface MAC addresses, nor the in-band management interfaces MAC ...


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However, would it be possible to craft an ethernet packet through a low level programming language (so it can bypass subnet checking) and simply send it over the wire to the switch ? Possible? Yes. Practical? No. Hosts consult their local routing table when trying to send a packet. On many platforms you can add a routing entry that causes the host to send ...


2

You are confusing a couple of things. What you need to understand is that any frames on the LAN are sent directly from host-to-host, not passing through the router. Host A sending a frame to Host B on the same ethernet network will address the frame with the MAC address of Host B. Frames containing packets destined for a different network are addressed to ...


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Ok, I think I found the answer (finally...) here: Manually configured and auto-generated sticky MAC address entries are automatically saved in a .ztbl or .ctbl file every 10 minutes. Alternatively, you can run the save command to manually save them. The saved file is not discarded after the device restarts. The file name must be the same as that of the ...


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Based on your comments, you do not seem to understand that any frames sent to that MAC address will arrive on that switch interface, regardless of whether or not the switch has the MAC address in its MAC address table. Switches will flood unknown unicast MAC addresses (those not in its MAC address table) to every switch interface A frame sent by Host2 will ...


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As we explained in your original question, the node to which this traffic should be flowing MUST send a frame for the connected switch to learn its location. And it must be a broadcast frame if you want the entire network to learn it. For IPv4, ARP takes care of this; IPv6 NDP. A gratuitous arp from a switch will only get the traffic to that switch, but not ...


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Does this mean that my computer allows unicast communications but not multicast? That indicates that your NIC's MAC is a unicast address - that's what it's supposed to be. The NIC also accepted broadcast and those multicasts that it is subscribed to - regardless of its hardware MAC. Think of the hardware MAC of the NIC's default address. It only accepts ...


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In complement to @Zac67 answer, take the case of a user than connect (to the workplace for example) through a VPN. It now has 2 options to send traffic to remote networks: sending the traffic as usual to its local gateway or send it trough the VPN tunnel. How can the host choose? Well, by looking up in its routing table, which is updated when the VPN tunnel ...


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all hosts have their local routing tables ...why? In addition to its local loopback interface, a host can have more than one external interface and on each interface more than one gateway. It needs to be able to make a routing decision, albeit with a usually very small routing table. Using a default gateway is only the simplest (and most common) scenario. ...


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