4 votes

What are EUI-48 and EUI-64?

In Ethernet the MAC address was and still is a 48 bit number used to identify Ethernet interfaces. Two bits are used for special purposes, one to indicate whether the address represented an individual ...
Peter Green's user avatar
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4 votes

Reach IP in a different subnet

Remember that IP addresses are always unique. The host 10.255.253.5 is configured with a /24 subnet mask, which means it sees 10.1.1.10 as on a different subnet. You need a router to route between ...
Ron Trunk's user avatar
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4 votes
Accepted

Adapting 10GBaseT and NBaseT with a PoE Injector?

"NBASE-T" or "MGBASE-T" is any speed from 2.5GBASE-T or 5GBASE-T (sometimes including 10GBASE-T). The best speed in common between a 10/100/1000/10GBase-T and a 10/100/1000/NBase-T ...
Zac67's user avatar
  • 83.9k
3 votes

Is there a way to find all MAC addresses in an Ethernet network?

Just take a look at the MAC table (also source address table) in your managed switch - each device having transmitted a frame within the mac aging period shows up in there. Other than that there's no ...
Zac67's user avatar
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3 votes
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Reach IP in a different subnet

I got a time out if I try to ping 10.255.253.5. Only ARP works. That is to be expected. When 10.1.1.10/8 tries to ping 10.255.253.5, it expects it to be "on link" = sharing the same ...
Zac67's user avatar
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3 votes

Is there a ping equivalent on layer 2?

I needed to verify connectivity between two layer2 endpoints. I used arping -bI <device> <random-ip-not-on-the-network> on one machine and tcpdmp -i <device> on the other end. When ...
AbduSami bin Khurram's user avatar
2 votes

Maximum packet size Ethernet Frame and IP packet

In short the exact definition of fragmentation is part of the answer. First, as some have answered, these are from specifications of ethernet and IP (IPv4). Since there are other Layer 2 (Data Link ...
Marlin Pierce's user avatar
2 votes

1000BASE-T with "no autonegotiation"

In all the PHYs that I have worked with, if Auto-Negotiation is disabled and speed is forced to 1000 Mbps, the PHY treats this as if Auto-Negotiation is enabled and the advertisement is limited to ...
claymation's user avatar
2 votes
Accepted

iSCSI silent data corruption

TCP checksums are only detecting errors - there's no correction, just retransmission. iSCSI is a protocol without a defined physical interface - so asking for its expected (undetected) error rate is ...
Zac67's user avatar
  • 83.9k
2 votes

100Mbps embedded device on a GbE network.. can I use MII?

A phy converts the electrical signals from the internal medium independent form to an external medium dependent form. However it does not have any buffer, it cannot change speeds. Going from a slower ...
Peter Green's user avatar
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2 votes

100Mbps embedded device on a GbE network.. can I use MII?

The MII is the interface between MAC and PHY - so you do need a PHY (PCS, PMA & PDM, with appropriate setup) to interface with anything. The Ethernet variants supported (100BASE-FX, 100BASE-TX, ...
Zac67's user avatar
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2 votes
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Confusion between MDI and MII

The MII (in its various incarnations RMII, GMII, SMII, ...) is the interface between the MAC and the PHY, ie. between data link layer and physical layer. The MII is entirely independent of the cable ...
Zac67's user avatar
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2 votes
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Do unmanaged switches automatically do bonding/multi-link?

No unmanaged switch will do this. You will create a loop and your network will break.
Teun Vink's user avatar
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2 votes
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Are integrated networking devices, frequently called routers, of the switch type or of a router / NIC type?

The devices that that quote seems to talk about are the ubiquitous (and off-topic here) integrated "routers" or "modems" that often include WAN PHY (DSL/cable modem) router with ...
Zac67's user avatar
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2 votes
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Negotiate at 10 Gbit/s but gain lower speeds due to issues?

With the notable exception of "Smartrate" ports supporting any subset of 2.5GBASE-T, 5GBASE-T, 10GBASE-T, Autonegotiation does not train the cable. If the Fast Link Pulses used for AN make ...
Zac67's user avatar
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2 votes
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Ethernet frame's source mac-address out of a port in an ARP request forwarded to an interconnected switch towards an end host

TL;DR ARP requests are broadcast, replies unicast. Source and destination MAC addresses in a frame don't change when it's forwarded. What will be the source mac-address in the "ethernet frame&...
Zac67's user avatar
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2 votes

same rack connection: better RJ45 or SFP?

Totally agreeing with Ron's answer for gigabit Ethernet. It becomes quite different with 10G Ethernet, where twisted pair requires significantly more power and increases latency in comparison to DACs ...
Zac67's user avatar
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2 votes

same rack connection: better RJ45 or SFP?

No difference in performance. Two SFPs and a fiber patch are more expensive than a Cat-6 jumper, but you already knew that.
Ron Trunk's user avatar
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2 votes

Is it possible that not adhering to a standard color coding in ethernet cables would affect performances?

The color coding scheme isn't technically required but it should be observed at all times for practical purposes - you wouldn't want to troubleshoot an installation where no reasonable scheme is used. ...
Zac67's user avatar
  • 83.9k
1 vote

Does Ethernet work at the FLIT level?

Ethernet doesn't use FLITs. The physical layer variants use various block codes, most prominently 4b5b, 8b10b and 64b66b. None of those use FLIT logic. Ethernet frame building starts on top of the ...
Zac67's user avatar
  • 83.9k
1 vote

Are the IEEE 802.3 Clause 40 1000BASE-T MDI-X signal names wrong?

I see your problem, when you look at each pin function. However, the pairs are called BI_Dx - bidirectional data, not Receive or Transmit like with 10BASE-T or 100BASE-TX. Think of BI_Dx as a named ...
Zac67's user avatar
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1 vote
Accepted

Is there any protocol between MAC layer and PHY layer?

If I read the IEEE 802.3 spec. correctly, there has no protocol between the MAC layer and PHY layer. There's a few signals such as signaling whether PHY is ready for transmission and whether MAC is ...
Zac67's user avatar
  • 83.9k
1 vote

Is there any protocol between MAC layer and PHY layer?

There are protocols such as HSRP, VRRP, and GLBP which work similar in which multiple devices share a virtual MAC address and IP address. When a host attempts to reach out to the default gateway, one ...
Peter F's user avatar
  • 11
1 vote

IP and Ethernet endianness

I wouldn't use the term endianness here. There's no general word size like with CPUs. Ethernet sends bytes as a bit stream, with the least significant bit first, with the notable exception of the FCS. ...
Zac67's user avatar
  • 83.9k
1 vote

rj45 ethernet coupler

Flat, round or any other form - all twisted-pair cables intended for Ethernet have the same pinout with pairs 1-2, 3-6, 4-5 and 7-8. Pin 2 is required for all Ethernet variants, even two-pair 10BASE-T ...
Zac67's user avatar
  • 83.9k
1 vote

Yealink & Aruba 1930 Switch Connection Issues

We were running into the same issue and, upon checking the switch configuration, we realized the EEE energy saving option was on. Turned it off and the phones stopped disconnecting. We spent months ...
Steve Jones's user avatar
1 vote
Accepted

Yealink & Aruba 1930 Switch Connection Issues

I think I have a solution. Being that the Aruba switches are relatively new, they have the latest features included. One of them is EEE (Energy Efficient Ethernet). In my case The Snom Phones are a ...
Sakkie's user avatar
  • 21
1 vote

Yealink & Aruba 1930 Switch Connection Issues

The switch log shows link down and a couple of seconds later link up. It does this the whole day every couple of minutes. If the physical link goes up and down, the problem is either switch port ...
Zac67's user avatar
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1 vote
Accepted

Cat5 Ethernet cable between buildings passes connectivity test but switch light not lighting up and no connectivity

Very often when a cable suddenly fails, the termination isn't good enough. Double check each side's termination, and if that doesn't help replace the cable. If you haven't done so, make sure no small ...
Zac67's user avatar
  • 83.9k
1 vote

OVS pop_mpls action returning invalid ethernet frames

As soon as I posted the question I suddenly knew the answer. The argument of mpls_pop defines the resulting ether type and NOT the mpls label to be popped. I changed it to 2048 (ipv4) and everything ...
Friwi's user avatar
  • 111

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