Duplicate MAC addresses

Am Samstag, 16. Juli 2022, um 19:49:41 Uhr schrieb Björn Lundin:

More than 1 IP for a single MAC is ok, but the same MAC 2 times creates problems when a switch or a bridge is being used because the port/MAC table will change every time a frame with the source MAC travels through the switch and the data won't reach its goal, it is mostly random on which port they will go out. It would be interesting what happens when 2 equal MAC addresses are used in a hub network or a bus. Maybe someone is willing to try that out in a test environment.

Am Samstag, 16. Juli 2022, um 19:55:01 Uhr schrieb A. Dumas:

A switch/bridge 8sometimes called multiport bridge) knows about the MAC addresses, it doesn't care about IPv4/IPv6. I am aware that layer3 switches exist, but these are just routers with another name and many switchports included. Additionally, a hub can either run 10BaseT half duplex or 100BaseTX half duplex. Some can handle both speeds and have an internal 2 port switch inside.

Hubs only exist for 10/100 MBit/s. For Gigabit I have never seen one. Some managed switched support a mirror mode that makes them act like a good old hub.

It is not just for Ethernet. It also works on e.g. WiFi and Decnet to name but two

Yes. Or rather the other way round - a one to many relation between mac addresses and IP addresses....

Am Samstag, 16. Juli 2022, um 23:57:41 Uhr schrieb The Natural Philosopher:

This does work and is common. Think about a host with the addresses 2001:db8::1234/64 and fe80::1234:acbd/64 on one interface (normal state). Both point to the same MAC address. If IPv4 is also in use, the IPv4 address also points to that MAC address. A problem is if 2 computers have the same IP address because (only if they don't implement DAD) they will both answer the ARP/NDP request. Such a situation must not exist in a network.

Am Samstag, 16. Juli 2022, um 23:56:16 Uhr schrieb The Natural Philosopher:

Is the ARP protocol for Ethernet different from ARP for WiFi? They both use MAC addresses, the only difference I know is that WiFi supports a hight MTU than Ethernet.

WiFi and ethernet (from 3Mbps thicknet to 100 gig fibre and beyond) are all members of the IEEE-802 family of protocols as such they have many things in common, in particular framing and addressing which means they can all be bridged. There are of course variations around the family - maximum MTU being one of them. The gigabit and up wired standards support "Jumbo" frames with the limit set in hardware (9000 bytes is a common safe figure) the card in this workstation apparently supports up to 16114 - but the switch at the other end only goes to 9000.

IME jumbo frames only really start to make a big difference at 10 gig and above where they're pretty much essential.

ARP is a protocol for resolving IPv4 addresses from hardware addresses in a broadcast-capable local net. IPv6 has its own neighbor discovery protocol.

Beside Ethernet, the current IANA hardware type catalog lists 39 other hardware types, including e.g. Token Ring, ARCNET, ATM and SDLC/HDLC.

That many? Wow. Blast from the past that lot are.

Am Sonntag, 17. Juli 2022, um 19:27:42 Uhr schrieb Tauno Voipio:

Could you please give a link? It would interest me. I only know Ethernet with its many standard like 10BaseT, 10Base2 etc. ARCNET, TokenRing/TokenBu and WiFi.

Here:

Look at Hardware Types.

cisco L3 switch, rather than cisco router?

AB> cisco L3 switch, rather than cisco router?

Cisco NCS540/55x1 mostly. I'd be surprised if our ASR's weren't the same, but I can't say I've looked.

Am Mittwoch, 20. Juli 2022, um 10:38:57 Uhr schrieb Andy Burns:

Despite the name - they do the same activities. Current cisco routers don't even allow routing based on physical ports. They also provide switching capabilities on all their ports.

agreed, but they sell devices they call switches, and they sell other devices they call routers.

even if you do a "no switchport" on the interface?

Andy Burns wrote:

My company deploys humble Cisco hardware. (Thank God almighty!) And, in my circumstance, the devices Cisco call routers do different activities than the devices they call switches. For instance, let's take a peek at the unique ip configuration subcommands for my humble routers:

------------------------------------------------------------------------ Global IP configuration subcommands: as-path BGP autonomous system path filter bgp-community format for BGP community bootp Config BOOTP services cef Cisco Express Forwarding classless Follow classless routing forwarding rules community-list Add a community list entry ddns Configure dynamic DNS default-network Flags networks as candidates for default routes dns Configure DNS server for a zone extcommunity-list Add a extended community list entry forward-protocol Controls forwarding of physical and directed IP broadcasts host-list Configure a host list identd Ident server mfib Multicast Forwarding mrm Configure IP Multicast Routing Monitor test parameters mroute Configure static multicast routes msdp MSDP global commands multicast Global IP Multicast Commands multicast-routing Enable IP multicast forwarding nat NAT configuration commands nbar NBAR - Network Based Application Recognition ospf OSPF pim PIM global commands policy-list Define IP Policy list prefix-list Build a prefix list rsvp Configure static RSVP information rtcp RTCP parameters sap Global IP Multicast SAP Commands sctp Global SCTP parameters traffic-export IP traffic export configuration commands trigger-authentication Trigger-authentication configurations parameters udptn UDPTN configuration commands vrf Configure an IP VPN Routing/Forwarding instance wccp Web-Cache Coordination Protocol Commands

------------------------------------------------------------------------

Here's the unique ip configuration subcommands offered on my humble routers:

------------------------------------------------------------------------ Global IP configuration subcommands: admission Network Admission Control (NAC) auth-proxy Authentication Proxy device Device tracking source IP source sticky-arp Allow the creation of sticky ARP entries

------------------------------------------------------------------------ Danke,

Andy Burns wrote:

My company deploys humble Cisco hardware. (Thank God almighty!) And, in my circumstance, the devices Cisco calls routers do different activities than the devices they call switches. For instance, let's take a peek at the unique ip configuration subcommands for my humble routers:

------------------------------------------------------------------------ Global IP configuration subcommands: as-path BGP autonomous system path filter bgp-community format for BGP community bootp Config BOOTP services cef Cisco Express Forwarding classless Follow classless routing forwarding rules community-list Add a community list entry ddns Configure dynamic DNS default-network Flags networks as candidates for default routes dns Configure DNS server for a zone extcommunity-list Add a extended community list entry forward-protocol Controls forwarding of physical and directed IP broadcasts host-list Configure a host list identd Ident server mfib Multicast Forwarding mrm Configure IP Multicast Routing Monitor test parameters mroute Configure static multicast routes msdp MSDP global commands multicast Global IP Multicast Commands multicast-routing Enable IP multicast forwarding nat NAT configuration commands nbar NBAR - Network Based Application Recognition ospf OSPF pim PIM global commands policy-list Define IP Policy list prefix-list Build a prefix list rsvp Configure static RSVP information rtcp RTCP parameters sap Global IP Multicast SAP Commands sctp Global SCTP parameters traffic-export IP traffic export configuration commands trigger-authentication Trigger-authentication configurations parameters udptn UDPTN configuration commands vrf Configure an IP VPN Routing/Forwarding instance wccp Web-Cache Coordination Protocol Commands

------------------------------------------------------------------------

Here's the unique ip configuration subcommands offered on my humble switches:

------------------------------------------------------------------------ Global IP configuration subcommands: admission Network Admission Control (NAC) auth-proxy Authentication Proxy device Device tracking source IP source sticky-arp Allow the creation of sticky ARP entries

------------------------------------------------------------------------ Danke,

Am Mittwoch, 20. Juli 2022, um 14:22:03 Uhr schrieb Andy Burns:

I haven't tried that yet.

Am Mittwoch, 20. Juli 2022, um 17:04:58 Uhr schrieb Don:

They have a different feature set, but the name L3 switch is just the same as router.

Some of their high performance routers also don't support NAT nor SPI firewalling. Some ISR models can be extended with licenses.

But from the specification, a layer 3 switch does the same as a router

- routing IP packets.